Java

The purpose of this page is to serve as a reference for the Java-curious user, to provide code to those interested, and to shameless reference our Java GitHub repository. This page contains a basic description of the general and technical aspects of the Java programming language, all the links an interested beginner would need, and a selection of more advanced Java snippets:

Java 101
Java Review
Java.java
Java Resources

Java 101

We recognize that the Java resources available online are much better than what we can provide, therefore, we will simply outline the general and technical aspects of the Java programming language and then provide links to, what we consider are the better Java resources. The facts of Java:

Uses:	Application, Mobile, Web, Business
Website:	java.com
Get Started:	Setting Up and Getting Started in Java Programming
Download:	java.com/download
Documents:	docs.oracle.com/java
Creator:	James Gosling
First Released:	January 23, 1996
Implementation:	Mostly Compiled with some Interpreted
Type Safety:	Strong
Type System:	Explicit
Type Checking:	Static
Imperative:	Yes
Aspect Oriented:	Yes
Object Oriented:	Yes
Functional:	Yes
Procedural:	Yes
Generic:	Yes
Reflective:	Yes
Event Driven:	Yes
Standardized:	Yes (Java Language Specification)
Failsafe I/O:	Yes
Garbage Collected:	Yes

As programmers, we are obligated to refer to the official documentation; and we suggest that new users try Oracle’s documentation. In the cases where the documentation is well formatted, written, and maintained (we’re looking at you Python), this usually works. If, for whatever reason, you are unable to stomach the Oracle documentation, or for those whom identify as the “visual” type, there is an abundance of online video and learning platforms that also provide proven Java content. Several resources we recommend, and occasionally utilize, are YouTube and the online courses at Udemy. YouTubers, such as Derek Banas, are great for a very fast overviews of a language or technology, where online courses like Udemy can have classes spanning dozens of hours. Finally, if new Java users want to develop in more than a text editor, then hunting for a Java Integrated Development Environment (IDE) may cause overchoice due to the large number of IDEs available. Java IDEs contains a lengthy list of possibilities; in the past we have used Eclipse and NetBeans, although currently we use IntelliJ CE (and are very satisfied with all it has to offer).

Java Review

As briefly outlined on the Projects page, mpettersson has a Java repository, named JavaReview publicly available on GitHub. The two main components of this repo are; first, a thorough review of basic Java syntax, and second, a series of programming questions and corresponding answers implemented in Java. The present majority of the programming questions are from the Cracking the Coding Interview book by Gayle Laakmann McDowell, however, more will be included from different sources in the future.

For the full repository, specifically the programming interview questions see github.com/mpettersson/JavaReview, or for the review component, continue reading below.

Java.java

This monstrous file, packed full of classes, is our Java review. Some of the code and topics demonstrated include:

Types
Control Flow
I/O
Provided Data Structures
Exception Handeling
Classes
Generics
Lambda Expressions
Streams
And Concurrency

In addition to being a simple Java language review, Java.java can be used as a concise tutorial for experienced programmers in other languages that are new to Java. The majority of the time, we simply use it as a single source of reference when we experience brain flatulence. Honestly, it ain’t pretty, but it works for us.



package com.mpettersson.review;


import org.junit.jupiter.api.*;
import org.junit.jupiter.api.Test;

import java.io.*;
import java.net.InetAddress;
import java.nio.file.*;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.*;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import static org.junit.jupiter.api.Assertions.*;


public class Java {

    // Enums
    public enum Day {Monday, Tuesday, Wednesday};


    public static void main(String[] args) {


        // Single line comment

        /**
         * Multi line comment, used by javadocs (documentation)
         */

        /*
            Multi line comment
         */

        ////////////////////////
        // NAMING CONVENTIONS //
        ////////////////////////
        /**
         *  PACKAGES
         *      - Always lowercase
         *      - Should be unique
         *      - Use your internet domain name reversed as prefix for package.
         *          - Replace invalid characters with underscore (_), i.e., experts-exchange.com --> com.experts_exchange
         *          - Domain name components starting with a number should start with an underscore (_), i.e., 1world.com --> com._1world
         *          - Domain name components that are java key words should start with an underscore (_), i.e., switch.supplier.com --> com.supplier._switch
         *
         *  CLASSES
         *      - CamelCase
         *          - Should start with a capital letter
         *          - Each word in the name should also start with a capital letter.
         *      - Should be a nouns.
         *
         *  INTERFACES
         *      - CamelCase
         *          - Should start with a capital letter.
         *          - Each word in the name should also start with a capital letter.
         *      - Can start with I (old convention)
         *
         *  METHODS
         *      - MixedCase
         *          - Should start with a lowercase letter.
         *          - Each word in the name should start with a capital letter.
         *      - Often Verbs
         *
         *  CONSTANTS
         *      - All upper case.
         *      - Separate words with an underscore (_)
         *      - Declare using the final keyword.
         *
         *  VARIABLES
         *      - MixedCase
         *          - Should start with a lowercase letter.
         *          - Each word in the name should start with a capital letter.
         *      - No underscores (_).
         *
         *  TYPE PARAMETERS
         *      - Single Capital Letter.
         *      - examples:
         *          E - Element
         *          K - Key
         *          V - Value
         *          S, U, V, etc. - 2nd, 3rd, 4th types.
         *          ? - Is the Unknown Type.
         *
         */


        ////////////////////////////
        // 8 PRIMITIVE DATA TYPES //
        ////////////////////////////

        // null is case sensitive in java, i.e., you CAN'T use NULL!
        // final variables can't be changed once initialized (can declare and define/initalize in two different lines).
        // Multiple variables of the same type can declared and assigned at once:  int a = 10, b = 11, c = 12;


        // BYTE - 8 bits
        final byte myMinByte = -128;
        byte myMaxByte = 127;
        byte byteCastExample = (byte) (myMinByte / 2);      // How to cast.

        // SHORT - 16 bits
        short myMinShort = -32768;
        short myMaxShort = 32767;

        // INT - 32 bits
        int myMinInt = -2_147_483_648;    // You can use underscores now...
        int myMaxInt = 2_147_483_647;

        // LONG - 64 bits
        long myMinLong = -9_223_372_036_854_775_808L;   // Need to put a 'L' or 'l' behind it.
        long myMaxLong = 9_223_372_036_854_775_807L;    // NOTE there isn't anything for short or byte.

        // FLOAT - 32 BITS -  7 decial digit percision
        float myFloatValue = 5F / 3f; // Should cast or use either 'F' or 'f' for float
        System.out.println("myFloatValue: " + myFloatValue);

        // DOUBLE - 64 BITS - has 16 decial digit percision
        // NOTE: USE DOUBLE OVER FLOAT, double is usually faster on modern computers and many of java's functions use it
        double myDoubleValue = 5d / 3D; // Should cast or use either 'D' or 'd' for double
        double pi = 3.141_592_7d;   // can use literals in numbers in java 7 or greater
        System.out.println("myDoubleValue: " + myDoubleValue);

        // CHAR - 16 bits, can be unicode or ASCII, remember there is only 128 ASCII...
        char myChar = '#';              // has to use single quotes.
        char copyrightChar = '\u00a9';  // can be unicode
        System.out.println("Unicode copyright char: '\\u00a9' = " + copyrightChar);
        System.out.println("ASCII to char: (char)42 = " + (char)42);
        System.out.println("Char to ASCII: (int)'*' = " + (int)'*');

        // BOOLEAN - No defined size
        boolean myBoolean = true;

        // boolean from string:
        boolean trueFlag = Boolean.valueOf("true");
        boolean falseFlag = Boolean.valueOf("false");


        // Primitive Type Values:
        System.out.println("Byte.TYPE: "        + Byte.TYPE);
        System.out.println("Byte.SIZE: "        + Byte.SIZE);
        System.out.println("Byte.MIN_VALUE: "   + Byte.MIN_VALUE);
        System.out.println("Byte.MAX_VALUE: "   + Byte.MAX_VALUE);

        System.out.println("Short.TYPE: "       + Short.TYPE);
        System.out.println("Short.SIZE: "       + Short.SIZE);
        System.out.println("Short.MIN_VALUE: "  + Short.MIN_VALUE);
        System.out.println("Short.MAX_VALUE: "  + Short.MAX_VALUE);

        System.out.println("Integer.TYPE: "     + Integer.TYPE);
        System.out.println("Integer.SIZE: "     + Integer.SIZE);
        System.out.println("Integer.MIN_VALUE: "+ Integer.MIN_VALUE);
        System.out.println("Integer.MAX_VALUE: "+ Integer.MAX_VALUE);

        System.out.println("Long.TYPE: "        + Long.TYPE);
        System.out.println("Long.SIZE: "        + Long.SIZE);
        System.out.println("Long.MIN_VALUE: "   + Long.MIN_VALUE);
        System.out.println("Long.MAX_VALUE: "   + Long.MAX_VALUE);

        System.out.println("Float.TYPE: "       + Float.TYPE);
        System.out.println("Float.SIZE: "       + Float.SIZE);
        System.out.println("Float.MIN_VALUE: "  + Float.MIN_VALUE);
        System.out.println("Float.MAX_VALUE: "  + Float.MAX_VALUE);

        System.out.println("Double.TYPE: "      + Double.TYPE);
        System.out.println("Double.SIZE: "      + Double.SIZE);
        System.out.println("Double.MIN_VALUE: " + Double.MIN_VALUE);
        System.out.println("Double.MAX_VALUE: " + Double.MAX_VALUE);

        System.out.println("Boolean.TYPE: "     + Boolean.TYPE);

        System.out.println("Character.TYPE: "               + Character.TYPE);
        System.out.println("Character.SIZE: "               + Character.SIZE);
        System.out.println("(int) Character.MIN_VALUE): "   + (int) Character.MIN_VALUE);
        System.out.println("(int) Character.MAX_VALUE): "   + (int) Character.MAX_VALUE);


        // Common Math Functions
        int x = 10, y = 100;
        double d = 1.0 / 3.0;
        System.out.println("Math.max(" + x + ", " + y + "): " + Math.max(x, y));
        System.out.println("Math.min(" + x + ", " + y + "): " + Math.min(x, y));
        System.out.println("Math.pow(" + x + ", " + y + "): " + Math.pow(x, y));
        System.out.println("Math.floorDiv(" + x + ", " + y + "): " + Math.floorDiv(x, y));
        System.out.println("Math.floorMod(" + x + ", " + y + "): " + Math.floorMod(x, y));
        System.out.println("Math.sqrt(" + x + "): " + Math.sqrt(x));
        System.out.println("Math.log(" + x + "): " + Math.log(x));
        System.out.println("Math.floor(" + d + "): " + Math.floor(d));
        System.out.println("Math.ceil(" + d + "): " + Math.ceil(d));
        System.out.println("Math.abs(" + x + "): " + Math.abs(x));
        System.out.println("Math.random():" + Math.random());  // Returns double >= 0.0 and < 1.0

        // How to get random values:
        System.out.println("Math.random():" + Math.random());  // Returns double >= 0.0 and < 1.0

        int bound = 10;
        int seed = 100;
        byte[] bytes = new byte[10];
        Random random = new Random();

        random.nextInt();  // Returns int >= Integer.MIN_VALUE and <= Integer.MAX_VALUE
        random.nextInt(bound);  // Returns int >=0 < bound, ONLY int can have bound.
        random.nextDouble();  // Returns double >= 0.0 and < 1.0
        random.nextBytes(bytes);  // Puts random bytes into each index of supplied array.
        random.nextBoolean();
        random.setSeed(seed);
        System.out.println("random.nextInt(): " + random.nextInt());
        System.out.println("random.nextInt(" + bound + "): " + random.nextInt(bound));
        System.out.println("random.nextDouble(): " + random.nextDouble());
        System.out.println("random.nextBytes(bytes): " + Arrays.toString(bytes));
        System.out.println("random.nextBoolean(): " + random.nextBoolean());
        System.out.println("random.setSeed(" + seed + ")");


        // COMPARETO
        //
        // NOTE: The object type must extend Comparable, i.e., class MyObject<T extends Comparable>
        //       Can't be primitive types (so use Integer for int, Double for double, etc...)
        //
        // Usage:
        //      myObjectLeft<T>.compareTo(myObjectRight<T>)
        //
        // Results:
        //      0 if myObjectLeft == myObjectRight
        //     -1 if myObjectLeft < myObjectRight   (it's -1 no matter size i.e., 1 < 2 or 1 < 2222)
        //      1 if myObjectLeft > myObjectRight   (it's 1 no matter size i.e., 2 > 1 or 2222 > 1)
        Integer one = 1;
        Integer negOne = -1;
        Integer six = 6;
        System.out.println(one + ".compareTo(" + one + ")" + one.compareTo(one));       // 1.compareTo(1)  == 0 (1 == 1)
        System.out.println(one + ".compareTo(" + six + ")" + one.compareTo(six));       // 1.compareTo(6) == -1 (1 < 6)
        System.out.println(six + ".compareTo(" + one + ")" + six.compareTo(one));       // 6.compareTo(1)  == 1 (6 > 1)
        System.out.println(one + ".compareTo(" + negOne + ")" + six.compareTo(negOne)); // 6.compareTo(-1) == 1 (6 > -1)


        /////////////
        // STRINGS //
        /////////////

        // Strings are a class/Object and not a primitive type.

        String myString = "This is my string!";
        String strHello = "Hello";
        String strWorld = "World";
        String eol = System.lineSeparator();

        // Concat with
        System.out.println(strHello + strWorld);        // This will automatically convert to string
        System.out.println(strHello.concat(strWorld));  // This WILL NOT automatically convert to string!!!

        // NOTE: You can assign null to a string, BUT, it'll cause exceptions with many of the common string ops.
        String nullString = null;
        System.out.println(nullString);

        String emptyString = "";

        // Find string length with <stringVar>.length();
        System.out.println("emptyString.length() = " + emptyString.length());

        // Find if string is empty (i.e., length == 0) with <stringVar>.isEmpty();
        System.out.println("emptyString.isEmpty() = " + emptyString.isEmpty());


        String example = "This should be complicated enough to show some things we should show";

        // Find the characters at the indexes given
        System.out.println(example.charAt(0));
        System.out.println(example.charAt(5));

        // An StringIndexOutOfBoundsException is thrown in both these cases:
        // System.out.println(example.charAt(-1));
        // System.out.println(example.charAt(200));

        // Find the index of characters or substrings
        System.out.println(example.indexOf('s'));                         // returns the first occurence of 's'
        System.out.println(example.indexOf('s', 4));        // the first 's' after index 4
        System.out.println(example.indexOf("should"));                    // the index of the first "should" in our string
        System.out.println(example.indexOf("should", 15));  // the index of the first "should" in our

        // Find the last index of characters or substrings
        System.out.println(example.lastIndexOf('s'));                    // returns the first occurence of 's' when we look backwards from the end of the string
        System.out.println(example.lastIndexOf('s', 45));      // searches for 's' backwards from the position 45
        System.out.println(example.lastIndexOf("should"));               // returns the position at which the substring 'should' appears, looking backwards from the end of the string
        System.out.println(example.lastIndexOf("should", 20)); // finds substring 'should' from position 20 backwards, and returns the position at which it begins

        // The compareTo() method compares the Unicode value of two strings and returns a NUMBER.
        System.out.println("a".compareTo("a"));
        System.out.println("a".compareTo("b"));
        System.out.println("1".compareTo("12345678"));

        // Get substrings with substring() method.
        System.out.println(example.substring(2));
        System.out.println(example.substring(5,11));

        // Trim off the leading and trailing whitespace with .trim()
        String ourString = "      Any non-leading and non-trailing whitespace is  \n  preserved       ";
        System.out.println(ourString.trim());


        // Printf: formatted output
        // %s   : strings
        // %d   : Integers
        // %f   : Floats/Doubles
        // %c   : Characters
        // %e   : Scientific Notation
        // %t   : Dates
        // %b   : Booleans
        // %o   : Octal
        // %h   : Hex

        // The format syntax is:    %[argument_index$][flags][width][.precision]conversion

        double ourDouble = 1123.9303;
        System.out.println(String.format("%f", ourDouble));
        System.out.println(String.format("%.3f", ourDouble)); // specifies that we only want 3 digits after decimal point
        System.out.println(String.format("%e", ourDouble));

        String formatString  = "what does precision do with strings?";
        System.out.println(String.format("%.8s", formatString)); // prints the first 8 characters of our string

        int ourInt = 123456789;
        // System.out.println(String.format("%.4d", ourInt)); // precision can't be used on ints

        // If our number has less than 6 digits, this will add extra 0s to the beginning until it does
        System.out.println(String.format("%06d", 12));

        // If our number has more than 6 digits, it will just print it out
        System.out.println(String.format("%06d", 1234567));

        // We can specify output width, with the output being aligned to the right if it's shorter than the given space. If it's
        // longer, everything gets printed. The || are added for demonstration purposes only
        System.out.println(String.format("|%20d|", 12));
        // Or we can align the output to the left
        System.out.println(String.format("|%-20d|", 12));

        // We can also easily print an octal/hexadecimal value of an integer
        System.out.println(String.format("Octal: %o, Hex: %x", 10, 10));

        String replaceString = "We really don't like the letter e here";

        System.out.println(replaceString.replace('e', 'a'));
        System.out.println(replaceString.replace("here", "there"));
        System.out.println(replaceString.replaceAll("e(r+)", "a"));
        System.out.println(replaceString.replaceFirst("e(r+)", "a"));


        // How to split a string using regex:
        String[] fruits = "apples, oranges, pears, pineapples".split(",");

        System.out.println(Arrays.toString(fruits));

        // Using trim() to clean up some of the items.
        for(int i = 0; i < fruits.length; i++) {
            fruits[i] = fruits[i].trim();
        }

        System.out.println(Arrays.toString(fruits)); // Arrays.toString() formats the output array on its own

        // This returns then prints an empty array, since every character is interpreted as something to be split at and ignored
        System.out.println(Arrays.toString("apples.oranges.pears.pineapples".split(".")));

        // The "regex safe" way of doing this would be
        System.out.println(Arrays.toString("apples.oranges.pears.pineapples".split(Pattern.quote("."))));

        // Splits our string to two substrings at most, completely ignoring all other occurrences of "."
        System.out.println(Arrays.toString("apples.oranges.pears.pineapples".split(Pattern.quote("."), 2)));

        // Split strings at new lines:
        String lines[] = myString.split("[\\r\\n]+");

        // Split strings at spaces:
        String spaces[] = myString.split("\\s+");

        // examples of String.join()
        String arrayOfStrings[] = {"1","2","3","4","5"};
        System.out.println(String.join("-", arrayOfStrings));
        System.out.println(String.join("-", Arrays.asList(arrayOfStrings))); // Works just fine with lists as well
        System.out.println(String.join("", arrayOfStrings));


        // How to convert a string to a char aray:
        System.out.println(Arrays.toString("How to convert a string to a Char Array".toCharArray()));

        // SORT STRING - No method to sort a string, but can do this:
        String stringToSort = "Hahaha, Sort ME!";
        char[] chars = stringToSort.toCharArray();
        Arrays.sort(chars);
        String sortedString = new String(chars);
        System.out.println(sortedString);


        // How to remove all whitespaces (and newlines) from a string:
        String strWithWhiteSpaces = "  S\ttring  wit h      white spa\n c e s !!!  ";
        System.out.println(strWithWhiteSpaces);
        System.out.println(strWithWhiteSpaces.replaceAll("\\s+", ""));


        //////////////////////////////////
        // STRINGBUILDER & STRINGBUFFER //
        //////////////////////////////////

        // StringBuffer - First, Thread Safe/Synchronized
        // StringBuilder - Second, NOT Thread Safe, Several times FASTER

        StringBuilder strBuilder = new StringBuilder("A Random Value");

        // How to check the current capacity
        System.out.println(strBuilder.capacity());
        // Get the length of the used string with .length()
        System.out.println(strBuilder.length());
        // Append
        // NOTE: It will automatically add to the capacity if needed.
        System.out.println(strBuilder.append(" Again And Again And Again And Again And Again And Again And Again"));
        // Replace
        System.out.println(strBuilder.replace(2, 7,"NONRANDOM"));
        // Delete:
        System.out.println(strBuilder.delete(15, 21));
        // Insert:
        System.out.println(strBuilder.insert(30, "String To Insert"));
        // Reverse:
        System.out.println(strBuilder.reverse());
        // Print:
        System.out.println(strBuilder);
        // Use this to assign to a string
        System.out.println(strBuilder.toString());


        ///////////
        // INPUT //
        ///////////

//        // Scanner Example:
//        Scanner sc = new Scanner(System.in);
//        System.out.print("Enter name: ");
//        if(sc.hasNextLine()){
//            String userName = sc.nextLine();
//            System.out.println("Hello " + userName);
//        }
//
//        // Scanner Example with different types:
//        Scanner scanner = new Scanner(System.in);
//        System.out.println("Enter your name: ");
//        String name = scanner.nextLine();
//        System.out.println("Your name is: " + name);
//        System.out.println("Enter your year of birth: ");
//        int year = scanner.nextInt();
//        NOTE YOU HAVE TO CALL scanner.nextLine() to handle the newline (enter) if you want to do nextLine() for a string.
//        scanner.nextLine();
//        System.out.println("Your age is: " + (2018 - year));
//        scanner.close();
//
//        // JOPtion Pane Dialog Box Example:
//        String jopName = JOptionPane.showInputDialog("Enter name");
//        System.out.println("Hello " + jopName);


        /////////////////////////////
        // CONTROL FLOW STATEMENTS //
        /////////////////////////////

        int someVar = 4;
        // Remember that assignment returns the value assigned, so it has some weird cases...
        if((someVar = 10) == 10){
            System.out.println("what");
        }

        boolean blah;

        if(blah = true){
            System.out.println("this is the 'if' with an assignment.");
        }

        // NOTE: Unlike other languages (python, C/C++, etc.) numbers cannot be used in place of booleans.
        // The following (commented out code), has an error ('Incompatible Types'):
        // if(1){ System.out.println("True"); }

        // Whitespace and indenting stuff...
        int anothervar=5;
        System.out.println(anothervar);

        int
                anotherMessedUp
                =
                5
                ;
        System.out.println(anotherMessedUp);


        String mySwitchString = "matt";
        switch(mySwitchString){
            case "matt":
                System.out.println("input was matt");
                break;
            case "no":
                System.out.println("input was no");
                break;
            default:
                System.out.println("blah");
        }

        // Can use byte, short, char, int, and Strings with switch statements.
        int switchValue = 1;

        switch(switchValue){
            case 1:
                System.out.println("Value was 1");
                break;

            case 2:
                System.out.println("Value was 2");
                break;

            case 3: case 4: case 5: // How to have multiple values in a case.
                System.out.println("Value was 3, 4, or 5.");

            default:
                System.out.println("In default case...");
                break; // Don't really need a break here, but it's probably good to add it.
        }


        int count = 1;
        while(count != 6){
            System.out.println("count value is " + count);
            count++;
        }

        for(int i = 6; i !=6; i++){
            System.out.println("count value is " + count);
        }

        count = 1;
        do{
            System.out.println("count value is " + count);

            if(count > 100){
                break;
            }
            count++;
        }while(count != 6);


        String numberAsString = "2018";

        int intNumber = Integer.parseInt(numberAsString);
        double doubleNumber = Double.parseDouble(numberAsString);
        System.out.printf("This is the value for intNumber: %d and this is the value for doubleNumber: %f.\n", intNumber, doubleNumber);


        ////////////
        // ARRAYS //
        ////////////

        System.out.println("\nArrays Examples");

        // PRIMITIVE ARRAYS:
        int[] myIntArray1 = new int[3];
        int[] myIntArray2 = {1, 2, 3};
        int[] myIntArray3 = new int[]{1, 2, 3};

        // CLASS/STRING ARRAYS:
        String[] myStringArray1 = new String[3];
        String[] myStringArray2 = {"a", "b", "c"};
        String[] myStringArray3 = new String[]{"a", "b", "c"};


        //Declare and Initialize in separate statements:
        String[] myStringArray4;
        myStringArray4 = new String[]{"a", "b", "c"};  // The cast is necessary.

        // Multidimentional
        int[][] multiDimArray = {{1,2}, {1,2}, {1,2}, {1,2}, {1,2}};

        // How to copy arrays:
        // NOTE: Anything other than primitive data types will have shallow copies.
        int a1[] = {1,2,3};
        int a2[] = Arrays.copyOf(a1, 3);
        System.out.println(a2[0] + " " + a2[1] + " " + a2[2]);

        // How to sort an Array:
        int a3[] = {8, 7, 5, 2, 1};
        Arrays.sort(a3);

        // How to print an Array:
        System.out.println("Arrays.toString(a3): " + Arrays.toString(a3));


        ////////////////////////////
        // COLLECTION (INTERFACE) //
        ////////////////////////////

        // A collection represents a group of objects, known as its elements. The Collection interface is the root
        // interface in the collection hierarchy, that is, List Set and Queue interfaces extend the Collection interface.
        // Although the Map interface does not extend/implement the Collection interface (because Map hash key value
        // paris), it is considered part of the Collections Framework.
        //
        // The Collection interface is in the java.util package, some of it's more important methods include size(),
        // isEmpty(), contains(),  iterator(), toArray(), add(E e) , remove(), clear(), equals(), and hashCode().
        //
        // The four major data structure types in the Collections Framework are List, Set, Queue, and Map.
        //
        // LIST
        // Lists are ordered collections (sequences) of items that are accessed via an integer index, and typically
        // allow duplicate values.  The following are implemented List classes:
        //      Vector - Synchronized, growable array of objects accessed via an int index.
        //      Stack - Synchronized, Last-In-First-Out (LIFO) stack of objects (extends Vector).
        //      ArrayList - NOT synchronized, resizeable array implementation of List, allows nulls.
        //      LinkedList - NOT synchronized, doubly-linked list implementation (extends AbstractSequentialList).
        //
        // SET
        // Sets are collections that do not allow duplicate elements, and model the mathematical set abstraction.  The
        // following are implemented Set classes:
        //      HashSet - NOT synchronized, Set implementation by HashMap, allows one null, NOT ordered.
        //      LinkedHashSet - NOT synchronized, Hashtable & LinkedList imp of Set, ordered via doubly-linked list.
        //      TreeSet - Not synchronized, NavigableSet implementation based on HashMap, allows one null, NOT ordered.
        //
        // QUEUE
        // Queues are "a collection designed for holding elements prior to processing".  Queues typically, but do not
        // necessarily, order elements in a FIFO (first-in-first-out) manner.  Among the exceptions are priority queues,
        // which order elements according to a supplied comparator, or the elements' natural ordering, and LIFO queues
        // (or stacks) which order the elements LIFO (last-in-first-out).  The implemented Queue classes are:
        //      ArrayDequeue - NOT synchronized, resizable-array imp of the Deque interface, nulls NOT allowed.
        //      PriorityQueue - NOT synchronized, unbounded priority queue (First-In-First-Out) based on a priority heap.
        //      NOTE: LinkedList implements Dequeue.
        //
        // MAP
        // A Map is an object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most
        // one value.  The Map interface is interesting in that it does not implement or extend any other class.
        // Implemented Map classes include:
        //      HashMap - NOT synchronized, Hashtable based imp of Map, allows null vals and 1 null key, no order guarantees.
        //      Hashtable - Synchronized, Hashtable imp of Map, null NOT allowed, NOT ordered.
        //      TreeMap - NOT synchronized, Red-Black tree based NavigableMap imp; (ordered) SORTED by keys.
        //      LinkedHashMap - NOT synchronized, HashTable & LinkedList imp of the Map interface, ordered via dlinkedlist.
        //      IdentityHashMap - NOT synchronized, HashTable based Map imp using reference-equality when comparing keys.
        //
        // To iterate over a collection, without modifying it, use the for-each loop (for(Element e: collection)...).
        // To iterate over and access collection elements use; Enumeration, Iterator, and ListIterator.
        //
        // ENUMERATION
        // The Enumeration Interface was the first iterator, present in JDK 1.0, and only works on legacy collections
        // (Vector and Hashtable).  Only three methods were provided; hasMoreElements(), nextElement(), and asIterator().
        // It can only iterate in a forward direction (and can't Remove/Add/Set elements).
        //
        // ITERATOR
        // Added in Java 1.2, "Iterator takes the place of Enumeration in the Java Collections Framework". Iterators can
        // read and remove elements on ALL Collection objects.  Iterator methods include: hasNext(), next(), remove, and
        // forEachRemaining().
        //
        // LISTITERATOR
        // ListIterator extends Iterator, is ONLY available to lists (only AbstractList implements it), allows for
        // Bi-Directional movement, and can add/remove/set elements.  ListIterator has hasNext(), next(), hasPrevious(),
        // previous(), nextIndex(), previousIndex(), remove(), set(E e) and add(E e) methods.
        //
        // NOTE: ListIterator has no "current" element, that it always lies between the element that would be returned
        // by a previous() call and the element that would be returned by a next() call, furthermore, the remove() and
        // set(E e) methods act on the last element returned by next()/previous().


        ///////////////////
        // VECTOR (LIST) //
        ///////////////////
        // IS Synchronized

        System.out.println("\nVector Example");

        // NOTE: You have to use Uppercase Integer here BC it needs classes not primitives.
        Vector<Integer> vector = new Vector<>();

        vector.add(0);                          // Add 0 (at END) -- Autoboxing will auto-convert int to Integer
        vector.add(Integer.valueOf(1));         // Add 1 (at END) -- So don't have to do Integer.valueOf()...
        vector.add(2);                          // Add 1 (at END)
        vector.add(2, 99);       // Add 99 at index 2
        vector.add(0, -0);       // Add -0 at index 0
        vector.addAll(Arrays.asList(5,6,7,8));  // Add all elements of a collection.
        vector.set(2, 22);                      // Set value at index 2 to 22
        vector.get(2);                          // Return value at index 2 -- Autoboxing will convert Integer to int.
        vector.get(0).intValue();               // Return value at index 0 -- So don't need to use intValue().

        for(Integer i: vector){/* do stuff */}          // Iterate Via Enhanced For Loop

        Iterator vectorIt = vector.iterator();          // Iterate Via ITERATOR
        while (vectorIt.hasNext()){vectorIt.next();}    // And hasNext() method.

        Object[] vectorObjArray = vector.toArray();     // How to convert a Vector to an Object Array:

        System.out.println("vector.toString(): "        + vector.toString());
        System.out.println("vector.get(2): "            + vector.get(2));
        System.out.println("vector.indexOf(0): "        + vector.indexOf(0));
        System.out.println("vector.lastIndexOf(0): "    + vector.lastIndexOf(0));
        System.out.println("vector.lastElement(): "     + vector.lastElement());
        System.out.println("vector.isEmpty(): "         + vector.isEmpty());
        System.out.println("vector.contains(2): "       + vector.contains(2));
        System.out.println("vector.capacity(): "        + vector.capacity());
        System.out.println("vector.size(): "            + vector.size());

        vector.remove(0);                 // Remove and return item in index 0
        vector.remove((Object) 2);              // Remove object matching 2 (no exception if no match).
        vector.clear();


        //////////////////
        // STACK (LIST) //
        //////////////////
        // Extends Vector.

        System.out.println("\nStack Example");

        Stack<Integer> stack = new Stack<>();

        stack.push(0);                            // Push 0 on stack (or end if viewed as list).
        for(int i = 1; i < 5; i++) { stack.push(i); }
        stack.add(99);                                  // Add 99 to top of stack (or end if viewed as list).
        stack.addAll(Arrays.asList(5,6,7,8));           // Add all of a collection to stack.
        stack.set(2, 22);                               // Set value at index 2 to 22
        stack.get(2);                                   // Return value at index 2

        for(Integer i: stack){/* do stuff */}           // Iterate Via Enhanced For Loop

        Iterator stackIt = stack.iterator();            // Iterate Via ITERATOR
        while (stackIt.hasNext()){stackIt.next();}      // And hasNext() method.

        Object[] stackObjArray = stack.toArray();       // How to convert to an Object Array:

        System.out.println("stack.get(2): "     + stack.toString());
        System.out.println("stack.get(2): "     + stack.get(2));
        System.out.println("stack.size(): "     + stack.size());
        System.out.println("stack.search(2): "  + stack.search(2));
        System.out.println("stack.peek(): "     + stack.peek());
        System.out.println("stack.empty(): "    + stack.empty());
        System.out.println("stack.pop(): "      + stack.pop());

        stack.pop();
        stack.remove(0);                          // Remove and return item in index 0
        stack.remove((Object) 2);                       // Remove object matching 2 (no exception if no match).
        stack.clear();


        //////////////////////
        // ARRAYLIST (LIST) //
        //////////////////////

        System.out.println("\nArrayList Example");

        ArrayList<Integer> arrayList = new ArrayList<>();

        arrayList.add(0);                           // Add 0 (at tail)
        arrayList.add(Integer.valueOf(1));          // Add 1 (at tail)
        arrayList.add(2);                           // Add 1 (at tail)
        arrayList.add(2, 99);        // Add 99 at index 2
        arrayList.add(0, -0);        // Add -0 at index 0
        arrayList.addAll(Arrays.asList(5,6,7,8));   // Add all of a collection.
        arrayList.set(2, 22);                       // Set value at index 2 to 22
        arrayList.get(2);                           // Return value at index 2
        arrayList.get(0).intValue();                // Return value at index 0

        for(Integer i: arrayList){/* do stuff */}           // Iterate Via Enhanced For Loop

        Iterator arrayListIt = arrayList.iterator();        // Iterate Via ITERATOR
        while (arrayListIt.hasNext()){arrayListIt.next();}  // And hasNext() method.

        Object[] arrayListObjArray = arrayList.toArray();   // How to convert to an Object Array:

        System.out.println("arrayList.toString(): "     + arrayList.toString());
        System.out.println("arrayList.get(2): "         + arrayList.get(2));
        System.out.println("arrayList.indexOf(0): "     + arrayList.indexOf(0));
        System.out.println("arrayList.lastIndexOf(0): " + arrayList.lastIndexOf(0));
        System.out.println("arrayList.isEmpty(): "      + arrayList.isEmpty());
        System.out.println("arrayList.contains(2): "    + arrayList.contains(2));
        System.out.println("arrayList.size(): "         + arrayList.size());

        arrayList.remove(0);                 // Remove and return item in index 0
        arrayList.remove((Object) 2);              // Remove object matching 2 (no exception if no match).
        arrayList.clear();


        ///////////////////////////////
        // LINKEDLIST (LIST & QUEUE) //
        ///////////////////////////////

        System.out.println("\nLinkedList Example");

        LinkedList<Integer> linkedList = new LinkedList<>();

        linkedList.add(0);                          // Add 0 (at tail)
        linkedList.add(Integer.valueOf(1));         // Add 1 (at tail)
        linkedList.add(2);                          // Add 1 (at tail)
        linkedList.add(2, 99);       // Add 99 at index 2
        linkedList.add(0, -0);       // Add -0 at index 0
        linkedList.addFirst(0);                  // Add 0 to head of linkedList
        linkedList.addLast(99);                  // Add 99 to tail of linkedList
        linkedList.addAll(Arrays.asList(5,6,7,8));  // Add all of a collection to stack.
        linkedList.set(2, 22);                      // Set value at index 2 to 22
        linkedList.get(2);                          // Return value at index 2.
        linkedList.get(0).intValue();               // Return value at index 0.
        linkedList.getFirst();                      // Return value at index 0.
        linkedList.getLast();                       // Return value at last index.

        for(Integer i: linkedList){/* do stuff */}              // Iterate Via Enhanced For Loop

        Iterator linkedListIt = linkedList.iterator();          // Iterate Via ITERATOR
        while (linkedListIt.hasNext()){linkedListIt.next();}    // And hasNext() method.

        Object[] linkedListObjArray = linkedList.toArray();     // How to convert to an Object Array:

        System.out.println("linkedList.toString(): "        + linkedList.toString());
        System.out.println("linkedList.get(2): "            + linkedList.get(2));
        System.out.println("linkedList.getFirst(): "        + linkedList.getFirst());
        System.out.println("linkedList.getLast(): "         + linkedList.getLast());
        System.out.println("linkedList.indexOf(0): "        + linkedList.indexOf(0));
        System.out.println("linkedList.lastIndexOf(0): "    + linkedList.lastIndexOf(0));
        System.out.println("linkedList.isEmpty(): "         + linkedList.isEmpty());
        System.out.println("linkedList.contains(2): "       + linkedList.contains(2));
        System.out.println("linkedList.size(): "            + linkedList.size());

        linkedList.remove(0);                 // Remove and return item in index 0
        linkedList.remove((Object) 2);              // Remove object matching 2 (no exception if no match).
        linkedList.removeFirst();
        linkedList.removeFirstOccurrence(0);
        linkedList.removeLast();
        linkedList.removeLastOccurrence(0);
        linkedList.clear();


        //////////////////////////
        // ARRAYDEQUEUE (QUEUE) //
        //////////////////////////

        // Poll/Element/Offer   are the same as
        // Remove/Peek/Add      except Remove/Peek throw Exceptions if there is no object.

        System.out.println("\nArrayDeque Example");

        ArrayDeque<Integer> arrayDeque = new ArrayDeque<>();

        arrayDeque.push(0);                      // Push 0 to head
        arrayDeque.add(0);                          // Add 0 (to tail)
        arrayDeque.add(2);                          // Add 1 (to tail)
        arrayDeque.addFirst(0);                  // Add 0 to head
        arrayDeque.addLast(99);                  // Add 99 to tail
        arrayDeque.addAll(Arrays.asList(5,6,7,8));  // Add all of a collection.
        arrayDeque.offer(99);                    // Add 99 to end.
        arrayDeque.offerFirst(-0);               // Add -0 at head
        arrayDeque.offerLast(-9);                // Add -0 at tail
        arrayDeque.getFirst();                      // Return value at index 0.
        arrayDeque.getLast();                       // Return value at last index.
        arrayDeque.peek();                          // Return (but doesn't remove) head.
        arrayDeque.element();                       // Return (but doesn't remove) head.

        for(Integer i: arrayDeque){/* do stuff */}                  // Iterate Via Enhanced For Loop

        Iterator arrayDequeueIt = arrayDeque.iterator();            // Iterate Via ITERATOR
        while (arrayDequeueIt.hasNext()){arrayDequeueIt.next();}    // And hasNext() method.

        Object[] ArrayDequeueObjArray = arrayDeque.toArray();       // How to convert to an Object Array:

        System.out.println("arrayDeque.toString(): "        + arrayDeque.toString());
        System.out.println("arrayDeque.peek(): "            + arrayDeque.peek());
        System.out.println("arrayDeque.element(): "         + arrayDeque.element());
        System.out.println("arrayDeque.getFirst(): "        + arrayDeque.getFirst());
        System.out.println("arrayDeque.getLast(): "         + arrayDeque.getLast());
        System.out.println("arrayDeque.lastIndexOf(0): "    + arrayDeque.pollFirst());
        System.out.println("arrayDeque.isEmpty(): "         + arrayDeque.isEmpty());
        System.out.println("arrayDeque.contains(2): "       + arrayDeque.contains(2));
        System.out.println("arrayDeque.size(): "            + arrayDeque.size());

        arrayDeque.pop();
        arrayDeque.remove(0);                   // Remove and return item in index 0
        arrayDeque.remove((Object) 2);             // Remove object matching 2 (no exception if no match).
        arrayDeque.removeFirst();
        arrayDeque.removeFirstOccurrence(0);
        arrayDeque.removeLast();
        arrayDeque.removeLastOccurrence(0);
        arrayDeque.clear();


        ///////////////////////////
        // PRIORITYQUEUE (QUEUE) //
        ///////////////////////////

        // null values are NOT allowed.
        // Objects must be comparable.
        // Head of the queue is has lowest priority.
        //
        // PriorityQueue Constructor Options:
        //    PriorityQueue()                       Uses default initial capacity (11) and natural ordering.
        //    PriorityQueue(Collection<E> c)        Creates PriorityQueue with elements in the specified collection.
        //    PriorityQueue(int initialCapacity)    Uses specified initial capacity and natural ordering.
        //    PriorityQueue(int i, Comparator<E> c) Uses specified init capacity (i) and uses comparator (c) for order.
        //    PriorityQueue(PriorityQueue<E> c)     Creates a PriorityQueue with ele in the specified priority queue.
        //    PriorityQueue(SortedSet<E> c)         Creates a PriorityQueue with elements in the specified sorted set.
        //
        // Poll/Element/Offer   are the same as
        // Remove/Peek/Add      except Remove/Peek throw Exceptions if there is no object.

        System.out.println("\nPriorityQueue Example");

        PriorityQueue<Integer> priorityQueue = new PriorityQueue<>();

        priorityQueue.add(2);                           // Add 0 (at END) -- Autoboxing will auto-convert int to Integer
        priorityQueue.add(Integer.valueOf(98));         // Add 1 (at END) -- So don't have to do Integer.valueOf()...
        priorityQueue.add(1);                           // Add 1 (at END)
        priorityQueue.addAll(Arrays.asList(56,8,7));    // Add all of a collection.
        priorityQueue.offer(0);                      // Add 99
        priorityQueue.peek();                           // Returns (doesn't remove) head element (or ele at zero index)
        priorityQueue.element();

        for(Integer i: priorityQueue){/* do stuff */}               // Iterate Via Enhanced For Loop

        Iterator priorityQueueIt = priorityQueue.iterator();        // Iterate Via ITERATOR
        while (priorityQueueIt.hasNext()){priorityQueueIt.next();}  // And hasNext() method.

        Object[] priorityQueueObjArray = priorityQueue.toArray();   // How to convert to an Object Array:

        System.out.println("priorityQueue.toString(): "        + priorityQueue.toString());
        System.out.println("priorityQueue.peek(): "            + priorityQueue.peek());
        System.out.println("priorityQueue.isEmpty(): "         + priorityQueue.isEmpty());
        System.out.println("priorityQueue.contains(2): "       + priorityQueue.contains(2));
        System.out.println("priorityQueue.size(): "            + priorityQueue.size());

        priorityQueue.poll();                            // Remove and return the lowest value element.
        priorityQueue.remove((Object) 51);               // Remove object matching 2 (no exception if no match).
        priorityQueue.clear();


        ///////////////////
        // HASHSET (SET) //
        ///////////////////

        // Uses HashMap.
        // NO Order.

        System.out.println("\nHashSet Example");

        HashSet<Integer> hashSet = new HashSet<>();

        hashSet.add(1);                           // Add 1
        hashSet.add(1);                           // Doesn't do anything; already there.
        hashSet.addAll(Arrays.asList(56,8,7));    // Add all of a collection.

        for(Integer i: hashSet){/* do stuff */}               // Iterate Via Enhanced For Loop

        Iterator hashSetIt = hashSet.iterator();        // Iterate Via ITERATOR
        while (hashSetIt.hasNext()){hashSetIt.next();}  // And hasNext() method.

        Object[] hashSetObjArray = hashSet.toArray();   // How to convert to an Object Array:

        System.out.println("hashSet.toString(): "        + hashSet.toString());
        System.out.println("hashSet.isEmpty(): "         + hashSet.isEmpty());
        System.out.println("hashSet.contains(2): "       + hashSet.contains(2));
        System.out.println("hashSet.size(): "            + hashSet.size());

        hashSet.remove((Object) 51);               // Remove object matching 2 (no exception if no match).
        hashSet.clear();


        /////////////////////////
        // LINKEDHASHSET (SET) //
        /////////////////////////

        // Uses HashMap & LinkedList.
        // IS ORDERED.

        System.out.println("\nLinkedHashSet Example");

        LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<>();

        linkedHashSet.add(1);                           // Add 1 (at tail).
        linkedHashSet.add(1);                           // Doesn't do anything; already there.
        linkedHashSet.addAll(Arrays.asList(56,8,7));    // Add all of a collection.

        for(Integer i: linkedHashSet){/* do stuff */}               // Iterate Via Enhanced For Loop

        Iterator linkedHashSetIt = linkedHashSet.iterator();        // Iterate Via ITERATOR
        while (linkedHashSetIt.hasNext()){linkedHashSetIt.next();}  // And hasNext() method.

        Object[] linkedHashSetObjArray = linkedHashSet.toArray();   // How to convert to an Object Array:

        System.out.println("linkedHashSet.toString(): "        + linkedHashSet.toString());
        System.out.println("linkedHashSet.isEmpty(): "         + linkedHashSet.isEmpty());
        System.out.println("linkedHashSet.contains(2): "       + linkedHashSet.contains(2));
        System.out.println("linkedHashSet.size(): "            + linkedHashSet.size());

        linkedHashSet.remove((Object) 51);               // Remove object matching 2 (no exception if no match).
        linkedHashSet.remove(999);                    // Removing nonexistent item is OK.
        linkedHashSet.clear();


        ///////////////////
        // TREESET (SET) //
        ///////////////////

        // IS ORDERED
        // Implemented as self balancing binary tree (Red Black Tree).
        // Elements must be homogeneous and comparable.

        System.out.println("\nTreeSet Example");

        TreeSet<Integer> treeSet = new TreeSet<>();

        treeSet.add(1);                           // Add 1.
        treeSet.add(1);                           // Doesn't do anything; already there.
        treeSet.addAll(Arrays.asList(5,6,8,7,9)); // Add all of a collection.
        treeSet.first();                          // Return first element (raises exception if none).
        treeSet.last();                           // Return last element (raises exception if none).
        treeSet.floor(10);                     // Returns highest valued element <= than supplied element (10).
        treeSet.ceiling(10);                   // Returns lowest valued element >= than than supplied ele (10).
        treeSet.lower(10);                     // Returns highest valued element < than than supplied ele (10) or null.
        treeSet.higher(10);                    // Returns lowest valued element > than supplied element (10) or null.

        for(Integer i: treeSet){/* do stuff */}         // Iterate Via Enhanced For Loop

        Iterator treeSetIt = treeSet.iterator();        // Iterate Via ITERATOR
        while (treeSetIt.hasNext()){treeSetIt.next();}  // And hasNext() method.

        Object[] treeSetObjArray = treeSet.toArray();   // How to convert to an Object Array:

        System.out.println("treeSet.toString(): "        + treeSet.toString());
        System.out.println("treeSet.first(): "           + treeSet.first());
        System.out.println("treeSet.last(): "            + treeSet.last());
        System.out.println("treeSet.pollFirst(): "       + treeSet.pollFirst());
        System.out.println("treeSet.pollLast(): "        + treeSet.pollLast());
        System.out.println("treeSet.lower(10): "         + treeSet.lower(10));
        System.out.println("treeSet.higher(10): "        + treeSet.higher(10));
        System.out.println("treeSet.floor(10): "         + treeSet.floor(10));
        System.out.println("treeSet.ceiling(10): "       + treeSet.ceiling(10));
        System.out.println("treeSet.isEmpty(): "         + treeSet.isEmpty());
        System.out.println("treeSet.contains(2): "       + treeSet.contains(2));
        System.out.println("treeSet.size(): "            + treeSet.size());

        treeSet.pollFirst();                      // Remove and Return first element.
        treeSet.pollLast();                       // Remove and Return last element.
        treeSet.remove((Object) 51);              // Remove object matching 2 (no exception if no match).
        treeSet.remove(999);
        treeSet.clear();


        ///////////////////////////////
        // HASHMAP & HASHTABLE (MAP) //
        ///////////////////////////////

        // HashMap ISN'T thread safe and allows ONE null key value.
        // Hashtable IS thread safe, just use synchronized blocks, but DOES NOT allow any null key values.
        // Another threadsafe possibility is Collections.synchronizedMap:
        // Example: Map<String, Integer> syncHashMap = Collections.synchronizedMap(new HashMap<>());

        System.out.println("\nHashMap/Hashtable Example");

        Map<String, Integer> hash = new HashMap<>();

        // Adding key-value pairs to a HashMap
        hash.put("One", 1);
        hash.put("Two", 2);
        hash.put("Three", 3);
        hash.put("Five", 5);
        hash.put("Six", 6);

        // Add a new key-value pair only if the key does not exist in the HashMap, or is mapped to `null`
        hash.putIfAbsent("Four", 8);
        // put() - How to modify a value.
        hash.put("Four", 4);
        // get()
        System.out.println("hash.get(\"Four\"): " + hash.get("Four"));
        // isEmpty()
        System.out.println("hash.isEmpty(): " + hash.isEmpty());
        // size()
        System.out.println("hash.size(): " + hash.size());
        // containsKey()
        System.out.println("hash.containsKey(\"One\"): " + hash.containsKey("One"));
        // containsValue()
        System.out.println("hash.containsValue(1): " + hash.containsValue(1));
        // remove(Key) - One arg
        System.out.println("hash.remove(\"Six\"): " + hash.remove("Six"));
        // remove(Key, Value) - Only removes if the Key is mapped to the Value, returns true or false.
        System.out.println("hash.remove(\"Five\", 5): " + hash.remove("Five", 5));
        // remove(<NonExistantKey>) returns null
        System.out.println("hash.remove(\"Nine\"): " + hash.remove("Nine"));


        Set<Map.Entry<String, Integer>> keysAndValueSet = hash.entrySet();
        System.out.println("hash.entrySet(): " + keysAndValueSet);

        // keySet()
        Set<String> keySet = hash.keySet();
        System.out.println("hash.keySet(): " + keySet);

        // values()
        Collection<Integer> valueSet = hash.values();
        System.out.println("hash.values(): " + valueSet);


        // Iterating using Java 8 forEach and lambda
        System.out.print("Iterate with forEach and lambda: ");
        hash.forEach((key, value) -> {
            System.out.print(key + "=>" + value + ", ");
        });

        // Iterating with entrySet using iterator()
        System.out.print("\nIterate with entrySet and iterator(): ");
        Set<Map.Entry<String, Integer>> hashMapEntries = hash.entrySet();
        Iterator<Map.Entry<String, Integer>> hashMapIterator = hashMapEntries.iterator();
        while (hashMapIterator.hasNext()) {
            Map.Entry<String, Integer> entry = hashMapIterator.next();
            System.out.print(entry.getKey() + "=>" + entry.getValue() + ", ");
        }

        // Iterating with entrySet using Java 8 forEach and lambda
        System.out.print("\nIterate with entrySety(), forEach, and lambda: ");
        hash.entrySet().forEach(entry -> {
            System.out.print(entry.getKey() + "=>" + entry.getValue() + ", ");
        });

        // Iterating with entrySet using simple for-each loop
        System.out.print("\nIterate with entrySet() and for-each loop: ");
        for(Map.Entry<String, Integer> entry: hash.entrySet()) {
            System.out.print(entry.getKey() + "=>" + entry.getValue() + ", ");
        }

        // Iterating with keySet
        System.out.print("\nIterate with keySet(): ");
        hash.keySet().forEach(key -> {
            System.out.print(key + "=>" + hash.get(key) + ", ");
        });

        System.out.println();


        /////////////////////////
        // EXCEPTIONS & ERRORS //
        /////////////////////////

        // The Exceptions and Errors are subclasses of Throwable and can be found in the java.lang package.
        //
        // ERRORS
        // A represent a serious problem that should not be caught, are often related to environment, and are
        // unrecoverable.  All Errors are "unchecked", or are not checked at compile time.
        // Examples include StackOverflowError, OutOfMemoryError, AssertionError, and VirtualMachineError.
        //
        // EXCEPTIONS
        // Are a "condition that a reasonable application might want to catch", and are often more related to the
        // application.  RuntimeException and all of it's subclasses are "unchecked" exceptions, all other Exceptions
        // are "checked" exceptions, or are checked at compile time, and must be added to a classes/methods throw clause.
        // Examples include IOException, ArrayIndexOutOfBoundsException, NullPointerException, and ClassCastException.

        System.out.println("\nExceptions Example");

        try{
            int badInt = 10/0;
        }catch (ArithmeticException ex){
            System.out.println("Can't divide by zero");
            System.out.println(ex.getMessage());
            System.out.println(ex.toString());
        // Catch two exceptions in one catch block
        } catch( NullPointerException | ArrayIndexOutOfBoundsException e) {
            System.out.println(e.getMessage());
        // Generic catch all:
        }catch (Exception ex){
            System.out.println(ex.getMessage());
        // Finally always executes (unless thread is killed), even if a return statement is in try body.
        }finally {
            System.out.println("Clean up here, Close DBs, Etc...");
        }

        // THROW A CUSTOM EXCEPTION
        try{
            throw new Exception("BAD STUFF");
        }catch (ArithmeticException ex){
            System.out.println("Can't divide by zero");
            System.out.println(ex.getMessage());
            System.out.println(ex.toString());
        }catch (Exception ex){
            System.out.println(ex.getMessage());
        }finally {
            System.out.println("Clean up here, Close DBs, Etc...");
        }


        ///////////
        // FILES //
        ///////////

        System.out.println("\nFile IO Examples");

        // How to CREATE and RENAME a file:
        File f1 = new File("f1.log");
        File f1NewName = new File("F1BU.log");
        try{
            if(f1.createNewFile()){
                System.out.println("File created");
                f1.renameTo(f1NewName);
                // NOTE: Delete DOES NOT work if you changed the name of the file:
                f1.delete();
            }else{
                System.out.println("File not created");
            }
        }catch (IOException e){
            e.printStackTrace();
        }

        // How to WRITE to a File:
        File f2 = new File("f2.txt");
        try{
            PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter(f2)));
            pw.println("This is sample text");
            pw.close();
        }catch (IOException e){
            e.printStackTrace();
        }

        // How to READ from a File:
        f2 = new File("f2.txt");
        try{
            BufferedReader br = new BufferedReader(new FileReader(f2));
            String text = br.readLine();
            while(text != null){
                System.out.println(text);
                text = br.readLine();
            }
            br.close();
        }catch (IOException e){
            e.printStackTrace();
        }


        // How to write BINARY DATA:
        File f3 = new File("f3.dat");
        FileOutputStream fos;
        try{
            fos = new FileOutputStream(f3);
            BufferedOutputStream bos = new BufferedOutputStream(fos);

            // NOTE: To write primitives you need DataOutputStream
            DataOutputStream dos = new DataOutputStream(bos);
            String name = "Matt";
            int age = 37;
            double bal = 1234.56;

            dos.writeUTF(name);
            dos.writeInt(age);
            dos.writeDouble(bal);
            dos.close();
        } catch (IOException e){
            e.printStackTrace();
        }


        // How to READ BINARY files
        f3 = new File("f3.dat");
        FileInputStream fis;
        try{
            fis = new FileInputStream(f3);
            BufferedInputStream bis = new BufferedInputStream(fis);

            DataInputStream dis = new DataInputStream(bis);
            System.out.println(dis.readUTF());
            System.out.println(dis.readInt());
            System.out.println(dis.readDouble());
            fis.close();

        } catch (IOException e){
            e.printStackTrace();
        }


        // How to get the Absolute and Canonical PATHS of FILES.
        try {
            System.out.println("Absolute Path: " + f3.getAbsolutePath());
            System.out.println("Canonical Path: " + f3.getCanonicalPath());
            System.out.println("Path: " + f3.getPath());
        }catch(IOException e){
            e.printStackTrace();
        }

        // How to get the PATH of the current working DIR:
        Path currentRelativePath = Paths.get("");
        String s = currentRelativePath.toAbsolutePath().toString();
        System.out.println("Current relative path is: " + s);

        // How to READ files from a DIRECTORY:
        File d1 = new File(s);
        System.out.print(s + ": ");
        if(d1.isDirectory()){
            File[] files = d1.listFiles();
            for(File f : files) System.out.print(f.getName() + " ");
        }
        System.out.println();


        // Check if a DELETE worked using java.io.File.delete()
        if(f1NewName.delete()) {
            System.out.println("File " + f1NewName.getName() + " deleted successfully");
        } else {
            System.out.println("Failed to delete the file " + f1NewName.getName() + ".");
        }

        // How to DELETE if a file exists using java.nio.file.files.deleteifexists(Path p):
        try {
            Files.deleteIfExists(Paths.get(f2.getAbsolutePath()));
            Files.deleteIfExists(Paths.get(f3.getAbsolutePath()));
        } catch(NoSuchFileException e) {
            System.out.println("No such file/directory exists");
        } catch(DirectoryNotEmptyException e) {
            System.out.println("Directory is not empty.");
        } catch(IOException e) {
            System.out.println("Invalid permissions.");
        }



        /////////////
        // CLASSES //
        /////////////

        // INTERFACE VS EXTENDS
        //    If the end class "IS" something (but WITHOUT additional functionality) then use EXTENDS
        //    If the end class "CAN" do something (but HAS additional functionality) then use INTERFACE.
        //    Interfaces are more flexible than abstract classes, abstracting the 'what' from the 'how'.
        //    Use interfaces on UNRELATED classes.


        // COMPOSITION VS INHERITANCE
        //    Composition (HAS A relation) is accomplished by including an INSTANCE of another class as a FIELD of your class
        //    Inheritance (IS A relation) is accomplished by by EXTENDING another class in your class

        // MISC. CLASS STUFF
        //    super. - used to access/call the parent class members.
        //    super() - Only way to call parent constructor, must be first statement in constructor.
        //    this. - used to call the current class members (fields and methods), can't use in static context.
        //    this() - Only way to call a constructor (used for CONSTRUCTOR CHAINING). Must be first statement.
        //    Constructor can't have call to both super() and this().
        //    If a class is final or has a private constructor it can't be subclassed.


        // 4 TYPES OF NESTED CLASS
        //    static nested class
        //    non-static nested class (inner class)
        //    local class (inner class in a scope block/method) -- not used often, in theory, helps with encapsulation.
        //    anonymous nested class (no class name) -- used only once, used a lot with attaching event handlers to
        //                                              buttons (for example, in android apps).


        // How to instantiate classes.
        Rectangle rectangle = new Rectangle(0,0, true, 10, 10);
        Circle circle = new Circle(0, 0 , true, 1);

        // How to determine if something is an instance of a specific class:
        if(rectangle instanceof Rectangle){
            System.out.println("(rectangle instanceof Rectangle) :" + (rectangle instanceof Rectangle));
        }


        SerializationReview.examples();
        LambdaReview.examples();
        StreamReview.examples();
        ConcurrentReview.examples();
        GCReview.examples();

        // How to exit; this terminates the currently running Java Virtual Machine. The argument serves as a status
        // code; by convention, a nonzero status code indicates abnormal termination.
        System.exit(0);

    } // END OF MAIN
}


class Shape{
    // STATIC MEMBER VARIABLE
    //   SHARED by all instances of the class. i.e., scanners or loggers.
    private static int numberOfShapes = 0;

    // Instance Variables aka Fields aka Member Variables.
    private double xLocation;
    private double yLocation;
    private boolean visible;

    // Constructor
    public Shape(double xLocation, double yLocation, boolean visible){
        this.xLocation = xLocation;
        this.yLocation = yLocation;
        this.visible = visible;
        numberOfShapes++;
    }

    // INSTANCE METHOD
    //   This method is created when the class is instantiated with the "new" keyword.
    public void instanceMethod(){
    }

    // STATIC METHODS
    //   CAN'T access instance methods and instance variables directly (NO this.<whatev>..).
    //   Are not made when class is instantiated.
    public static void staticMethod(){
    }

    // MULTIPLE METHOD ARGS
    public static void multipleArgsMethod(int ... vals){
        for(int x : vals){
            // Do something...
        }
    }

    // See child class for Method Overriding.
    public void methodOverridingExample(){
    }

    // Deprecated!
    // A method called before object is garbage collected (Not a destructor, but often compared to a destructor).
    // Only use for logging.
    public void finalize(){
    }
}

// EXTENDS SHAPE
class Rectangle extends Shape{
    private double width;
    private double heigth;

    // CONSTRUCTOR CHAINING
    public Rectangle(double x, double y, boolean visible){
        this(x, y, visible, 0, 0);
    }

    public Rectangle(double xLocation, double yLocation, boolean visible, double width, double heigth){
        super(xLocation, yLocation, visible);
        this.width = width;
        this.heigth = heigth;
    }

    // METHOD OVERLOADING
    //   Must have same name, must have different parameters, CAN have different return types, CAN have different
    //   modifiers, CAN throw different checked or unchecked exceptions.
    public void methodOverloadExample(){

    }
    private boolean methodOverloadExample(int x){
        return true;
    }

    // METHOD OVERRIDING
    //   JVM will determine what method will be called at RUNTIME.  SHOULD (but don't have to) annotate with @Override.
    //   CAN'T override static methods (only instance methods).
    //   Only inherited methods can be overridden, constructors and private and final methods CAN'T be overridden.
    //   Use: super.methodName() to call the superclass version of an overridden method.
    //   MUST have same name and args, return type CAN be a subclass of the return type in the parent class,
    //   it CAN'T have a lower access modifier (if parent is protected then private child ISN'T allowed, can be public)
    @Override
    public void methodOverridingExample(){
    }
}

class Circle extends Shape{
    private double radius;
    public Circle(double x, double y, boolean visible, double radius){
        super(x, y, visible);
        this.radius = radius;
    }
}


//////////////////////
// ABSTRACT CLASSES //
//////////////////////

abstract class AbstractClassEmpty {
}

// CAN EXTENDS or IMPLEMENT in an abstract class.
abstract class AbstractClass extends AbstractClassEmpty implements InterfaceClassEmpty {

    // Can have member variables that are inherited (can't in interface unless static).
    private String name;

    // Can have a constructor (interfaces can't)
    public AbstractClass(String name){
        this.name = name;
    }

    // Can have non-abstract methods (that have bodies) in an abstract class
    public String getName() {
        return name;
    }

    // Remember that any class that implements (extends) this class must implement ALL of the things defined in this,
    // Where if they extended a base class, they can choose what they want to implement.

    // Only methods (and class) are allowed to be abstract.
    // Methods that are abstract don't have bodies (but you can have non-abstract methods that must have bodies in an abstract class).
    public abstract void doSomething();
    public abstract void doSomethingElse(int someInt);
}


class Teeest extends AbstractClass{

    public Teeest(){
        super("blah");
    }
    public void doSomething(){
        return;
    }
    public void doSomethingElse(int someInt){
        return;
    }
}

////////////////
// INTERFACES //
////////////////

interface InterfaceClassEmpty {
}

interface IAnotherEmptyClass{

}

// An interface can ONLY extend an interface (can't implement an interface, can't extend an abstract class).
interface InterfaceClass extends InterfaceClassEmpty, IAnotherEmptyClass{

    // Can ONLY have public static variables.
    public static String staticString = "Only static variables are allowed.";
    public static final int STATIC_INT = 838;

    // Pre-Java9, Can ONLY have public methods (no private or protected).
    public void interfaceMethod();
    public boolean interfaceMethodWithArg(int i);

    // SINCE JAVA 9, Interfaces can have private methods.
    //private void privateMethod();

    // SINCE JAVA 8, Interfaces can contain default methods (with implementation).
    default void defaultMethod(int defaultArg){
        System.out.println("Can actually implement something (have a body of a method in an Interface).");
    }
}


//////////////
// GENERICS //
//////////////


// Generics enable types (classes and interfaces) to be parameters when defining classes, interfaces and methods.
// Added to Java5
// Benefits include code reuse, type safety, elimination of casts, and ability for generic algorithms.


interface InterfaceGenericClass<T>{
}

abstract class AbstractGenericClass<T>{

}

// Can have multiple types:
class ClassWithGenerics<T extends Comparable, U>{

    T val;

    public void setVal(T val){
        this.val = val;
    }

    // Static generic method:
    // Static keyword must have matching Generic type if generic type used anywhere in method.
    // Static generic methods can be used in non-generic classes.
    public static<T extends Object> void staticMethod(T[] arr){
        System.out.println("I'm staticMethod in ClassWithGenerics...");
    }

    public T getVal(){
        return val;
    }

    public void usingRawAndGenerics() {
        // List using raw types:.
        ArrayList rawTypesList = new ArrayList();
        rawTypesList.add(1);
        rawTypesList.add("hi");
        rawTypesList.add(1.2);

        // List using generics:
        ArrayList<Integer> intList = new ArrayList<>();
        intList.add(144);
    }

    // Must typecast when referencing; prone to run time errors.
    public static void printArrayList(ArrayList<?> aL){
        for(Object x : aL) System.out.println(x);
    }
}


////////////////
// COMPARATOR //
////////////////

// Comparator interface is used to order the objects of user-defined classes.
// A comparator object is capable of comparing two objects of two different classes.

// Usage Example:
//        String[] stringArray = new String[]{"they", "fun", "race", "fights", "care", "listens", "silent", "acre"};
//        Arrays.sort(stringArray, new AnagramComparator());

// This example would sort each string in a string array so that anagrams would be ordered next to each other.
class AnagramComparator implements Comparator<String>{
    public String sortChars(String s){
        char[] content = s.toCharArray();
        Arrays.sort(content);
        return new String(content);
    }

    // Must implement compare when implementing Comparator.
    public int compare(String s1, String s2){
        return sortChars(s1).compareTo(sortChars(s2));
    }

    // How to implement a Comparator as an Anonymous Class (Say if you wanted to do this in main()):
    public void howToImplementComparatorViaAnonymousClass(){
        String[] stringArray = new String[]{"they", "fun", "race", "fights", "care", "listens", "silent", "acre"};
        Arrays.sort(stringArray, new Comparator<String>() {
            @Override
            public int compare(String s1, String s2) {
                char[] content1 = s1.toCharArray();
                Arrays.sort(content1);
                char[] content2 = s2.toCharArray();
                Arrays.sort(content2);
                return (new String(content1)).compareTo(new String(content2));
            }
        });
    }
}


///////////////////////////////////////////////////
// SERIALIZATION (SERIALIZABLE & EXTERNALIZABLE) //
///////////////////////////////////////////////////

// Serialization, in Java, is the process which is used to serialize object in java by storing object’s state into a
// file and recreating object's state from that file (the reverse process is called deserialization).  The file (byte
// stream) created is platform independent, therefore, an object serialized on one platform can be deserialized on a
// different platform.  This is useful for network communication and to save objects states.
//
// NOTE: Any object being serialized (from an serialized object) MUST ALSO be serialized or a
// java.io.NotSerializableException will be thrown.
//
// The Java Serialization API provides the Serializable interface and the Externalizable interface as object
// serialization mechanisms.
//
// SERIALIZABLE INTERFACE
// Serializable is a MARKER INTERFACE, or, an interface that has no methods or constants inside it, and is intended to
// provide information to the compiler and JVM.  Therefore, to make a class Serializable, add "implements
// java.io.Serializable", then the JVM will provide default serialization.  The default serialization is serialization
// of all non-static and non-transient data members.  Variables defined with transient keyword are initialized with the
// default value (NOT current value) during deserialization. Variables defined with static keyword are loaded with the
// current value of the variable during deserialization.
//
// EXTERNALIZABLE INTERFACE
// The Externalizable interface, which extends Serializable, allows for flexibility and control of object serialization
// via writeExternal() and readExternal() methods.  When overriding these two methods, the user can specify/customize
// the items that are read and written, thus, allowing for better control and backwards compatibility.  Contrary to the
// Serializable interface, the Externalizable interface CAN write/read transient and static variables.
//
// NOTE: The same items and order must be used during writing (writeExternal()) and reading (readExternal()).
// NOTE: There must be a public default no-arg constructor to use readObject() on an object that implemented
//       Externalizable, or a java.io.InvalidClassException will be thrown.
//
// SERIALVERSIONUID
// The Serialization runtime associates a version number with each Serializable class called, this number is the
// serialVersionUID.  This is used during Deserialization to verify that the sender and receiver of a serialized object
// have loaded compatible classes (w.r.t. serialization). If the serialVersionUID differ during Deserialization, then a
// InvalidClassException will be thrown.  If no serialVersionUID is defined, Java will automatically create one based on
// the class'es attributes (note that small changes in the class can cause a different ID).  It is considered good
// practice to define your own serialVersionUID; to do this, define "static final long serialVersionUID" and assign it
// to a type of long value.
//
// SERIALVER
// serialver is a tool that comes with JDK. It is used to get serialVersionUID number for Java classes. The tool is used
// via the following command:
//      serialver [-classpath classpath] [-show] [classname…]


class SerializationReview{
    public static void examples(){

        SerializableClass serializableClass = new SerializableClass();
        SerializableClass readSerializableClass = null;

        serializableClass.transientInt = 8008;
        serializableClass.staticInt = 6;
        serializableClass.string = "Hello World!";
        serializableClass.i = 42;

        ExternalizableClass externalizableClass = new ExternalizableClass();
        ExternalizableClass readExternalizableClass = null;

        externalizableClass.transientInt = 80085;
        externalizableClass.staticInt = 69;
        externalizableClass.string = "Hello World!!!";
        externalizableClass.i = 420;

        System.out.println(serializableClass.toString());
        System.out.println(externalizableClass.toString());

        try {
            // Serialize serializableClass:
            ObjectOutputStream so = new ObjectOutputStream(new FileOutputStream("serializableClass.txt"));
            so.writeObject(serializableClass);
            so.flush();
            so.close();

            // Serialize externalizableClass:
            so = new ObjectOutputStream(new FileOutputStream("externalizableClass.txt"));
            so.writeObject(externalizableClass);
            so.flush();
            so.close();

            serializableClass.transientInt = 800;
            serializableClass.staticInt = -6;
            serializableClass.string = "Hello!";
            serializableClass.i = 4;

            externalizableClass.transientInt = 800850;
            externalizableClass.staticInt = 690;
            externalizableClass.string = "Hello World!!!!!!!!!!!";
            externalizableClass.i = 4200;

            // Deserialize serializableClass:
            ObjectInputStream si = new ObjectInputStream(new FileInputStream("serializableClass.txt"));
            readSerializableClass = (SerializableClass)si.readObject();
            si.close();

            // Deserialize externalizableClass:
            si = new ObjectInputStream(new FileInputStream("externalizableClass.txt"));
            readExternalizableClass = (ExternalizableClass)si.readObject();
            si.close();

            // Delete files:
            File f = new File("serializableClass.txt");
            f.delete();
            f = new File("externalizableClass.txt");
            f.delete();

        } catch (Exception e) {
            System.out.println(e);
        }

        System.out.println(readSerializableClass.toString());
        System.out.println(readExternalizableClass.toString());

    }
}

// To make a class serializable just implement java.io.Serializable; it's easy, but consider long term implications...
class SerializableClass implements java.io.Serializable{

    // It is considered good practice to specify a serialVersionUID.
    private static final long serialVersionUID = 123456789L;
    transient int transientInt;
    static int staticInt;
    String string;
    int i;

    public String toString() {
        return ("serialVersionUID: " + serialVersionUID + " transientInt: " + transientInt + " staticInt: " + staticInt
                + " string: " + string + " i: " + i);
    }
}

// To make a class externalizable add implements Externalizable, then, add both writeExternal() and readExternal()
// methods; this is also easy, but please consider the long term implications...
class ExternalizableClass implements Externalizable{

    // It is considered good practice to specify a serialVersionUID.
    private static final long serialVersionUID = 1234567890L;
    transient int transientInt;
    static int staticInt;
    String string;
    int i;

    // NOTE: When implementing Externalizable, there MUST be a default no-arg constructor to prevent a
    // java.io.InvalidClassException when readObject is called on a file (of the serialized object).
    public ExternalizableClass(){}

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        // NOTE: ORDER WRITTEN MUST MATCH ORDER READ.
        out.writeObject(string);
        // Can write/read transient and static variables with Externalizable.
        out.writeInt(transientInt);
        out.writeInt(staticInt);
        // Using Externalizable, I can choose not to serialize something by not writing it:
        // out.writeInt(i);
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        // NOTE: ORDER READ MUST MATCH ORDER WRITTEN.
        string = (String)in.readObject();
        staticInt = in.readInt();
        transientInt = in.readInt();
    }

    public String toString() {
        return ("serialVersionUID: " + serialVersionUID + " transientInt: " + transientInt + " staticInt: " + staticInt
                + " string: " + string + " i: " + i);
    }
}



////////////////////////////////////////////////////
// LAMBDA EXPRESSIONS // aka FUNCTIONAL INTERFACE //
////////////////////////////////////////////////////

// Lambda Expressions can ONLY be used with interfaces that contain only one method that HAS to be implemented.
// java.util.function contains functional interfaces designed to be used with Lambda Expressions.
// If the body of the Lambda Expression has more than one statement you need to add curly braces ({}) and a return.
// Local variables referenced from a Lambda Expression must be final or effectively final.

class LambdaReview {
    public static void examples(){

        // NOTE: Lambda Expressions can easily replace Anonymous Classes with single methods.
        //       Lambda must return same type for all branches.

        // Simple comparator using lambda:
        Comparator<String> comp = (first, second) -> Integer.compare(first.length(), second.length());

        // How to start a runnable (thread) via Anonymous Class:
        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("This is a thread that only prints then dies.");
            }
        }).start();

        // A LAMBDA EXPRESSION for RunnableCode.
        new Thread(() -> System.out.println("This is a thread that only prints then dies.")).start();

        // LAMBDA CONSUMER (via accept(), 1 or 2 args, DOESN'T RETURN a value, CAN be Chained).
        Consumer<String> print = s -> System.out.println(s);
        // Use Lambda Consumer via accept() method:
        print.accept("my string");

        // LAMBDA PREDICATE (via test(), 1 or 2 args, RETURNS a value, CAN'T be Chained).
        Predicate<Integer> even = i -> i % 2 == 0;
        // Use Lambda Predicate via test() method:
        System.out.println(even.test(2));

        // LAMBDA SUPPLIER (via get(), ZERO args, RETURNS a value, CAN'T be Chained).
        Random random = new Random();
        Supplier<Integer> randomSupplier = () -> random.nextInt(1000);
        // Use Lambda Supplier via get() method:
        System.out.println(randomSupplier.get());

        // LAMBDA FUNCTIONS (via apply(), 1 or 2 args, RETURNS a value, CAN be Chained).
        Function<String, String> trim = (String s) -> { return s.trim(); };
        Function<String, Integer> length = s -> s.length();
        // Use Lambda Function via apply() method:
        System.out.println(trim.apply("     t r   i     m       e   d     "));

        // CHAINED Lambda Functions
        Function chainedFunctions = trim.andThen(length);
        System.out.println(chainedFunctions.apply("     t r   i     m       e   d     "));

        // LAMBDA UNIARY OPERATOR (1 argument, RETURNS same type as arg, CAN be Chained).
        IntUnaryOperator add5 = i -> i + 5;
        System.out.println(add5.applyAsInt(10));

        // LAMBDA FOREACH
        List<String> stringList = Arrays.asList("a", "b", "c", "d", "e", "f", "g", "h");
        stringList.forEach(num -> System.out.println(num));

    }
}


/////////////////////////
// STREAM (COLLECTION) //
/////////////////////////

// Added in Java 8
// A stream is not a data structure instead it takes input from the Collections, Arrays or I/O channels.
// Streams don’t change the original data structure, they only provide the result as per the pipelined methods.
// Streams are composed of Intermediate and Terminal Operations

class StreamReview{
    public static void examples(){

        // NOTE: METHOD REFERENCE OPERATOR (:: or DOUBLE COLON)
        //   Used to call a method by referring to it with the help of its class directly.
        //   The only difference to lambda expressions is that :: uses direct reference to the method by name instead
        //   of providing a delegate to the method.
        //   Example: .map(String::toUpperCase) behaves as .map(s->s.toUpperCase())

        List<Integer> numbers = Arrays.asList(2,2,3,4,5,3,6,7,8,9);
        List<String> names = Arrays.asList("Matthew", "Brenton", "mark", "ryan", "Chris", "Bob", "michelle");


        // STREAM INTERMEDIATE OPERATIONS (Lazily Executed, Returns a Stream)
        //   Intermediate Operations can be pipelined or chained together.
        //   Each intermediate operation is lazily executed and returns a stream as a result.
        //   NOTE: An Intermediate Operation must have a Terminal Operation, or a return to be executed.

        // MAP (Returns a stream of the results of applying a function to the elements of the stream)
        List<Integer> listInteger = numbers.stream().map(x-> x * x ).collect(Collectors.toList());
        Stream<Integer> streamInt = numbers.stream().map(x-> {return x * x;});

        // FILTER (Filter selects elements as per the Predicate argument).
        List<String> filteredNames = names.stream().filter(s->s.startsWith("M")).collect(Collectors.toList());

        // SORTED (Sorts the Stream)
        List<String> sortedNames = names.stream().sorted().collect(Collectors.toList());

        // PEEK (Mainly For Debugging)
        names.stream().filter(e -> e.length() > 4)
                      .peek(e -> System.out.println("Remaining value: " + e))
                      .collect(Collectors.toList());

        // LIMIT (Returns a stream of the elements truncated to be no longer than maxSize in length)
        List<Integer> firstTwo = numbers.stream().sorted().limit(2).collect(Collectors.toList());

        // DISTINCT (Returns a stream of distinct elements
        List<Integer> distinctNumbers = numbers.stream().distinct().collect(Collectors.toList());

        // MAX (Returns the max element of the stream according to the provided comparator)
        Integer max = numbers.stream().max(Integer::compare).get();

        // MIN (Returns the min element of the stream according to the provided comparator)
        Integer min = numbers.stream().min(Integer::compare).get();


        // STREAM TERMINAL OPERATIONS (Returns a Result)
        //   Terminal operations mark the end of the stream and return the result (primitive, collection, or no value).
        //   Terminal operations are typically preceded by intermediate operations.

        // GET (Returns a value, if one is present, else throws NoSuchElementException)
        Integer maxNumber = numbers.stream().max(Integer::compare).get();

        // COLLECT (Returns the result of the Intermediate Operation(s))
        Set<Integer> squareSet = numbers.stream().map(x->x*x).collect(Collectors.toSet());

        // FOREACH (Iterates through every element of a Stream)
        numbers.stream().map(x->x*x).forEach(y->System.out.println(y));

        // REDUCE (Reduces the elements of a stream to a single value via a BinaryOperator)
        int even = numbers.stream().filter(x->x%2==0).reduce(0,(ans,i)-> ans+i);

        // COUNT (Returns, AS LONG, the number of elements in the stream)
        long count = numbers.stream().distinct().count();

        // TOARRAY (Returns an array of the elements of this stream, using the provided generator function)
        Integer[] intArray = numbers.stream().map(x->x*x).toArray(Integer[]::new);
    }
}


////////////////
// CONCURRENT //
////////////////

class ConcurrentReview {
    public static final String EOF = "EOF";



    //////////////
    // VOLATILE //
    //////////////

    // The volatlie keyword/modifier guarantees that any thread that reads a field will access the most recently written
    // value (as opposed to a cached value) and NOTHING about mutual exclusion (so multiple threads can still access the
    // field).  Therefore, use of the volatile keyword without synchronization CAN cause memory consistency errors.
    //
    // AtomicBoolean can be used in place of volatile.
    //
    // HOWEVER, java.util.concurrent.atomic supports lock-free thread-safe programming on single variables.
    static volatile boolean volatileFlag = true;


    public static void examples() {
        List<Thread> threadList = null;



        ////////////
        // THREAD //
        ////////////

        // Threads, aka light weight processes, consists of; a program counter, registers, stack, and state and run in
        // shared memory space.  Threads can communicate with other threads (of the same process) directly by using
        // methods like wait(), notify(), notifyAll() (where processes must use inter-process communication).
        //
        // Threads can be created via:
        //   (1) Extend the java.lang.Thread class.
        //   (2) Implement the java.lang.Runnable interface
        //   (3) Implement the java.util.concurrent.Callable interface using FutureTask and a Thread
        //
        // The most common methods for a thread are:
        //   getName()	    Obtain thread’s name
        //   getPriority()	Obtain thread’s priority
        //   isAlive()	    Determine if a thread is still running
        //   join(timeout)	Wait for a thread to terminate
        //   run()	        Entry point for the thread
        //   sleep()	    Suspend a thread for a period of time
        //   start()        Start a thread by calling its run method


        // THREAD VIA ANONYMOUS THREAD CLASS
        new Thread(){public void run() { System.out.println("I'm an Anonymous Thread Class Thread"); }}.start();


        // THREAD VIA ANONYMOUS RUNNABLE
        new Thread(new Runnable() {public void run() { System.out.println("I'm a Anonymous Runnable Thread"); }}).start();


        // THREAD VIA LAMBDA THREAD EXPRESSION
        new Thread(()->{System.out.println("I'm a Lambda Thread Expression");}).start();


        // THREADS VIA LAMBDA RUNNABLE EXPRESSION
        Runnable runnable = () -> {System.out.println("I'm a Lambda Runnable Expression");};
        new Thread(runnable).start();


        // THREAD VIA EXTEND THREAD
        //   This prevents a class from extending anything else.
        //   Cannot return a value.
        //   Cannot throw exceptions.
        class ClassExtendingThread extends Thread {
            @Override
            public void run() {
                try {
                    System.out.println("ClassExtendingThread Thread " + Thread.currentThread().getId() + " is running");
                } catch (Exception e) {
                    System.out.println ("Exception is caught");
                }
            }
        }
        ClassExtendingThread classExtendingThread = new ClassExtendingThread();
        classExtendingThread.start();


        // THREAD VIA IMPLEMENTS RUNNABLE
        //   More flexible than extending Thread
        //   Single Abstract Method Type
        //   Cannot return a value.
        //   Cannot throw exceptions.
        class ClassImplementingRunnable implements Runnable {
            @Override
            public void run() {
                try {
                    System.out.println ("ClassImplementingRunnable Thread " + Thread.currentThread().getId() + " is running");
                } catch (Exception e) {
                    System.out.println ("Exception is caught");
                }
            }
        }
        Thread threadRunnable = new Thread(new ClassImplementingRunnable());
        threadRunnable.start();


        // THREADS VIA IMPLEMENTS CALLABLE USING FUTURETASK AND THREAD
        //   Added in Java 5
        //   Single Abstract Method Type
        //   Can return a result (Future object)
        //   call() method can throw Checked exception.
        class ClassImplementingCallable implements Callable<String> {
            @Override
            public String call() {
                String str = null;
                try {
                    str = "ClassImplementingCallable Thread " + Thread.currentThread().getId() + " is RETURNED this string!";
                } catch (Exception e) {
                    System.out.println ("Exception is caught");
                }
                return str;
            }
        }
        Callable<String> callable = new ClassImplementingCallable();
        FutureTask<String> futureTask = new FutureTask(callable);
        Thread threadCallable = new Thread(futureTask);
        threadCallable.start();
        try{
            System.out.println("FutureTask value: " + futureTask.get());
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }



        /////////////////////
        // SYNCHRONIZATION //
        /////////////////////

        // The synchronized keyword restricts multiple threads from executing code simultaneously on the same object
        // instance; synchronized can be used on a METHOD or a CODE BLOCK.  Every object (EXCLUDING Primitives) has an
        // Implicit lock, sometimes called a monitor.  In Java, Synchronization is implemented with monitors.
        // Only one thread can own a monitor at a given time. When a thread acquires a monitor, it is said to have
        // entered the monitor. All other threads attempting to enter the locked monitor will be suspended until the
        // first thread exits the monitor.
        //
        // Java uses java uses wait(), notify() and notifyAll() to better coordinate thread interactions, these methods
        // belong to the OBJECT Class, hence, are available to all classes:
        //   wait()         Thread will go to waiting state, releasing the monitor, wakes when notified by another thread.
        //   notify()       Wakes one (other) thread waiting on the same monitor, does not give up the monitor.
        //   notifyAll()    Wakes all (other) threads that are waiting (called wait()) on the same object.  Might have
        //                  performance issues if many threads are present.


        // Class implementing SYNCHRONIZED METHOD and SYNCHRONIZED CODE BLOCK:
        class Message{
            private String message;
            private boolean empty = true;
            // SYNCHRONIZED METHOD EXAMPLE
            public synchronized String read(){
                while(empty){
                    try{
                        wait();
                    }catch(InterruptedException ex){
                        System.out.println("Exception: " + ex.toString());
                    }
                }
                empty = true;
                notifyAll();
                return message;
            }
            // SYNCHRONIZED CODE BLOCK EXAMPLE
            // Static methods use:      synchronized(ClassName.class){ ... }
            // Non-Static methods use:  synchronized(this){ ... }
            public void write(String message){
                synchronized (this) {
                    while (!empty) {
                        try {
                            wait();
                        } catch (InterruptedException ex) {
                            System.out.println("Exception: " + ex.toString());
                        }
                    }
                    empty = false;
                    this.message = message;
                    notifyAll();
                }
            }
        }

        // Thread to write to synchronized object.
        class Writer implements Runnable {
            private Message message;
            public Writer(Message message) {
                this.message = message;
            }
            public void run() {
                String messages[] = {"Humpty","Dumpty","sat","on","a","wall","Humpty","Dumpty","had","a","great","fall",
                        "All","the","king's","horses","and","all","the","king's","men","Couldn't","put",
                        "Humpty","together","again"};
                Random random = new Random();
                for(int i=0; i<messages.length; i++) {
                    message.write(messages[i]);
                    try {
                        Thread.sleep(random.nextInt(100));
                    } catch(InterruptedException e) {
                        System.out.println("Exception: " + e.toString());
                    }
                }
                message.write("Finished");
            }
        }

        // Thread to read from synchronized object.
        class Reader implements Runnable {
            private Message message;
            public Reader(Message message) {
                this.message = message;
            }
            public void run() {
                Random random = new Random();
                for(String latestMessage = message.read(); !latestMessage.equals("Finished");
                    latestMessage = message.read()) {
                    System.out.print(" " + latestMessage);
                    try {
                        Thread.sleep(random.nextInt(100));
                    } catch(InterruptedException e) {
                        System.out.println("Exception: " + e.toString());
                    }
                }
            }
        }


        // SYNCHRONIZATION EXAMPLE
        Message message = new Message();
        threadList = new ArrayList<>();
        threadList.add(new Thread(new Writer(message)));
        threadList.add(new Thread(new Reader(message)));
        threadList.stream().forEach(x->x.start());
        for(Thread t : threadList) {
            try {
                t.join(5000);
            } catch (InterruptedException e) {
                System.out.println("Exception: " + e.toString());
            }
        }
        System.out.println();



        ///////////////////
        // REENTRANTLOCK //
        ///////////////////

        // ReentrantLock synchronizes access to a shared resource by associating the resource with the reentrantLock,
        // NOT via a synchronized method or synchronized code block.  A thread gets access to a shared resource by first
        // acquiring the reentrantLock associated with the resource.  At any given time, at most one thread can hold the
        // reentrantLock and access the resource.
        //
        // The most common reentrantLock methods are:
        //   reentrantLock()        Get reentrantLock if available; if not, the thread gets blocked until the lock is released.
        //   lockInterruptibly()    Similar to reentrantLock(), but it allows the blocked thread to be interrupted and
        //                          resume the execution through a thrown java.lang.InterruptedException.
        //   tryLock()              Non-blocking version of reentrantLock(); attempts to get the lock, if successful RETURNS true.
        //   tryLock(timeout)       Similar to tryLock(), except it waits up the given timeout before giving up.
        //   unlock()               Unlocks the Lock instance
        //   lock()                 If lock unavailable then current thread lies dormant until the lock has been acquired.
        //
        // In addition to the Lock interface, there is the ReadWriteLock interface which maintains a pair of locks, one for
        // read-only operations, and one for the write operation. The read reentrantLock may be simultaneously held by
        // multiple threads as long as there is no write.
        //
        // The rules for acquiring the ReadLock or WriteLock by a thread:
        //   Read Lock – If no thread acquired the write reentrantLock, or requested it, then multiple threads can acquire
        //               the read reentrantLock.
        //   Write Lock – If no threads are reading or writing, then only one thread can acquire the write reentrantLock.



        class MyProducer implements Runnable {
            private List<String> buffer;
            private Lock lock;
            public MyProducer(List<String> buffer, Lock lock) {
                this.buffer = buffer;
                this.lock = lock;
            }
            public void run() {
                Random random = new Random();
                String[] nums = { "1", "2", "3", "4", "5"};
                for(String num: nums) {
                    try {
                        System.out.println(Thread.currentThread() + " Adding..." + num);
                        lock.lock();
                        try {
                            buffer.add(num);
                        } finally {
                            lock.unlock();
                        }
                        Thread.sleep(random.nextInt(100));
                    } catch(InterruptedException e) {
                        System.out.println("Producer was interrupted");
                    }
                }
                System.out.println(Thread.currentThread() + " Adding EOF and exiting...");
                lock.lock();
                try {
                    buffer.add("EOF");
                } finally {
                    lock.unlock();
                }
            }
        }

        class MyConsumer implements Runnable {
            private List<String> buffer;
            private Lock lock;
            public MyConsumer(List<String> buffer, Lock lock) {
                this.buffer = buffer;
                this.lock = lock;
            }
            public void run() {
                while(true) {
                    lock.lock();
                    try {
                        if(buffer.isEmpty()) {
                            continue;
                        }
                        if(buffer.get(0).equals(EOF)) {
                            System.out.println(Thread.currentThread() + " Exiting");
                            break;
                        } else {
                            System.out.println(Thread.currentThread() + " Removed " + buffer.remove(0));
                        }
                    } finally {
                        lock.unlock();
                    }
                }
            }
        }

        // A shared "Buffer" or resource.
        List<String> buffer = new ArrayList<>();

        // REENTRANT LOCK EXAMPLE
        ReentrantLock reentrantLock = new ReentrantLock();

        threadList = new ArrayList<>();
        threadList.add(new Thread(new MyProducer(buffer, reentrantLock)));
        threadList.add(new Thread(new MyConsumer(buffer, reentrantLock)));
        threadList.add(new Thread(new MyConsumer(buffer, reentrantLock)));
        threadList.add(new Thread(new MyProducer(buffer, reentrantLock)));
        threadList.stream().forEach(x->x.start());
        for(Thread t : threadList) {
            try {
                t.join(5000);
            } catch (InterruptedException e) {
                System.out.println("Exception: " + e.toString());
            }
        }




        ///////////////
        // EXECUTORS //
        ///////////////

        // Executors are used for creating and managing threads. Added in Java 5. Some of the benefits include:
        //   Returns Future Objects
        //   Scheduling (via ScheduledExecutorService).
        //   Optimized cost overheads; reuses threads to decrease creation/cleanup overhead.
        //   Decouples task submission from task execution.
        //   Controls processing of tasks ( Work Stealing, ForkJoinPool, invokeAll) etc.
        //   Monitors the progress and health of Threads.
        //   Work Stealing (via newWorkStealingPool()) in JAVA 8
        //
        // ExecutorService common methods:
        //   execute()      Submits a Callable or a Runnable task to an ExecutorService (returns void).
        //   submit()       Submits a Callable or a Runnable task to an ExecutorService and returns a result of type FUTURE.
        //   invokeAny()    Submits a COLLECTION of tasks to an ExecutorService, and returns ONE FUTURE result, if successful.
        //   invokeAll()    Submits a COLLECTION of tasks to an ExecutorService, and returns the results of ALL task executions
        //                  in the form of a list of objects of type FUTURE aka List<Future<String>>.
        //   shutdown()     ExecutorService stops accepting new tasks, waits for previously submitted tasks to execute, then
        //                  terminates the executor.  DOESN'T shut down immediately.
        //   shutdownNow()  this method interrupts the running task and shuts down the executor immediately.
        //
        // Future Object common methods:
        //   get()          (BLOCKING) Returns an actual result of the Callable task's execution or null if Runnable task.
        //   isDone()       Used to check if the assigned task is already processed, returns BOOLEAN.
        //   cancel(true)   Cancels task execution, takes boolean mayInterruptIfRunning, returns BOOLEAN (false if couldn't cancel).
        //   isCancelled()  Checks if task was cancelled, returns BOOLEAN.


        // EXECUTOR, EXECUTORSERVICE, FUTURE OBJECTS EXAMPLE
        // Create a thread pool that reuses a fixed number of threads operating off a shared unbounded queue.
        ExecutorService executorServiceFixedPool = Executors.newFixedThreadPool(2);

        // NOTE: For SCHEDULED Threads use: Executors.newScheduledThreadPool(int corePoolSize);

        // NOTE: For WORK STEALING Threads use: Executors.newWorkStealingPool(int parallelism)!!!
        //       newWorkStealingPool(int parallelism) Creates a thread pool that creates new threads as needed via the
        //       provided ThreadFactory, and will reuse previously constructed threads when they are available

        // Use execute() on Classes that extended Threads OR implemented Runnable
        executorServiceFixedPool.execute(new ClassExtendingThread());
        executorServiceFixedPool.execute(new ClassImplementingRunnable());

        // A List for Future Objects returned by the ExecutorService:
        List<Future<String>> futureList = new ArrayList<>();

        // Use submit() on Classes that Implemented Callable, can get returned FutureObject
        futureList.add(executorServiceFixedPool.submit(new ClassImplementingCallable()));

        // To Convert Classes that extended Thread OR implemented Runnable to Callable Executors.callable(new myClass):
        Callable<String> callableT = Executors.callable(new ClassExtendingThread(), "ClassExtendingThread Done!");
        Callable<String> callableR = Executors.callable(new ClassImplementingRunnable(), "ClassImplementingRunnable Done!");
        futureList.add(executorServiceFixedPool.submit(callableT));
        futureList.add(executorServiceFixedPool.submit(callableR));

        // Use get(1000, TimeUnit.MILLISECONDS) (with timeout) to get the returned Future Objects (Strings):
        try {
            for(Future future : futureList) {
                System.out.println(future.get(1000, TimeUnit.MILLISECONDS));
            }
        } catch ( TimeoutException | InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }

        // Oracle recommended shut down for ExecutorService:
        executorServiceFixedPool.shutdown();
        try{
            if(!executorServiceFixedPool.awaitTermination(800, TimeUnit.MILLISECONDS)){
                executorServiceFixedPool.shutdownNow();
            }
        }catch(InterruptedException e){
            executorServiceFixedPool.shutdownNow();
        }



        ///////////////////////
        // FORK/JOIN THREADS //
        ///////////////////////

        // Fork/Join adds divide-and-conquer, or recursive task processing.  Added in Java 7. Benefits include:
        //   Work Stealing (An idle thread steals work from a thread having tasks queued more than it can process)
        //   Ability to recursively decompose the tasks and collect the results.
        //
        // To make use of ForkJoin's recursive task processing, extend RecursiveAction (a task with return type void)
        // OR RecursiveTask<Object> (a task that returns a result) and implement/Override the compute() method.
        // The compute() method defines subtasks (instances of your class) and forks them via .fork().


        // FORK/JOIN FORKJOINPOOL EXAMPLE
        class ClassExtendingRecursiveTask extends RecursiveTask<Long> {
            private long workLoad = 0;
            public ClassExtendingRecursiveTask(long workLoad) { this.workLoad = workLoad; }
            @Override
            protected Long compute() {
                if(this.workLoad > 16) {                                                            // THREASHOLD
                    System.out.println("Splitting : " + this.workLoad);
                    List<ClassExtendingRecursiveTask> subtasks = new ArrayList<>();
                    subtasks.addAll(createSubtasks());
                    for(ClassExtendingRecursiveTask subtask : subtasks){
                        subtask.fork(); }                                                           // FORK
                    long result = 0;
                    for(ClassExtendingRecursiveTask subtask : subtasks) {
                        result += subtask.join(); }                                                 // JOIN
                    return result;
                } else { System.out.println("Computing: " + this.workLoad); return workLoad * 3; }
            }
            private List<ClassExtendingRecursiveTask> createSubtasks() {
                List<ClassExtendingRecursiveTask> subtasks = new ArrayList<>();
                subtasks.add(new ClassExtendingRecursiveTask(this.workLoad / 2));
                subtasks.add(new ClassExtendingRecursiveTask(this.workLoad / 2));
                return subtasks;
            }
        }

        // Create a ForkJoinPool with the specified level of parallelism. The parallelism == number of task threads/CPUs.
        ForkJoinPool forkJoinPool = new ForkJoinPool(4);

        ClassExtendingRecursiveTask recursiveTask = new ClassExtendingRecursiveTask(75);

        // Performs the given task, returning its result upon completion
        long mergedResult = forkJoinPool.invoke(recursiveTask);
        System.out.println("mergedResult = " + mergedResult);



        /////////////
        // PROCESS //
        /////////////

        // Java provides java.lang.Process for process related tasks.
        // Two common ways to start a process are ProcessBuilder.start() and Runtime.getRuntime.exec(); both methods
        // creates a native process and return an instance (of a subclass of java.lang.Process) that can be used to
        // control the process and get information about it.
        //
        // ProcessBuilder was added in JAVA 5 and is preferred over Runtime due to the following reasons:
        //   Can change the working directory our shell command is running in using builder.directory().
        //   Can set-up a custom key-value map as environment using builder.environment().
        //   Redirects input and output streams to custom replacements.
        //   Can inherit both of them to the streams of the current JVM process using builder.inheritIO()
        //
        // Common Process methods include:
        //   destroy()          Kills the subprocess.
        //   exitValue()        Returns the exit value, as INT, for the subprocess.
        //   getErrorStream()   Returns the INPUTSTREAM of the subprocess.
        //   getOutputStream()  Returns OUTPUTSTREAM of the subprocess; output is piped into the std input stream.
        //   waitFor()          (BLOCKING) Returns the exit code, as INT, returned by the process.
        //   isAlive()          Returns BOOLEAN true if the process is still alive.
        //   destroyForcibly()  Destroys the process by force.

        // How to get OS name/type (so our process example can call the right app).
        String operSys = System.getProperty("os.name").toLowerCase();
        String line;
        if(operSys.contains("mac")) {
            try {


                // PROCESS VIA RUNTIME EXAMPLE
                System.out.println("Runtime Example");
                Runtime runtime = Runtime.getRuntime();
                // NOTE: Runtime exec can take a single string delimited by spaces.
                Process runtimeProcess = runtime.exec(String.format("sh -c ls"));

                // INPUT STREAM
                BufferedReader runtimeInputStream = new BufferedReader(new InputStreamReader(runtimeProcess.getInputStream()));
                while ((line = runtimeInputStream.readLine()) != null) {
                    System.out.print(line + " ");
                }
                System.out.println();

                // WAIT FOR
                System.out.println("exitcode: " + runtimeProcess.waitFor());


                // PROCESS VIA PROCESS BUILDER
                System.out.println("ProcessBuilder Example");
                // NOTE: ProcessBuilder requires a list of strings (args must be a list too).
                ProcessBuilder processBuilder = new ProcessBuilder(new String[]{"sh", "-c", "ls"});
                processBuilder.directory(new File(System.getProperty("user.home")));
                Process processBuilderProcess = processBuilder.start();

                // INPUT STREAM
                BufferedReader pbInputStream = new BufferedReader(new InputStreamReader(processBuilderProcess.getInputStream()));
                while ((line = pbInputStream.readLine()) != null) {
                    System.out.print(line + " ");
                }
                System.out.println();

                // WAIT FOR
                System.out.println("exitcode: " + runtimeProcess.waitFor());

            }catch(IOException | InterruptedException ex){
                System.out.println("Caught Exception: " + ex.toString());
            }
        } else {
            // TODO Add condition for your OS here...
            System.out.println("TODO Add condition for your OS here...");
        }



    }

}



////////////////////////////
// GC (GARBAGE COLLECTOR) //
////////////////////////////
//
// To understand the Garbage Collector system, we must first understand the JVM and JVM memory management.
//
// The Java Virtual Machine (JVM) acts as a run-time engine to run Java applications, and is a part of Java Runtime
// Environment (JRE).  The JVM memory management system is divided into several main parts; the Stack, Heap, and
// Permanent Generation.
//
// JVM STACK
// For each thread the JVM creates a stack.  JVM stack memory does not need to be contiguous. The JVM pushes and pops
// frames off the stack; stack frame consists of three parts:
//      Local Variable Array: A zero-based, indexed, array of words,
//      Operand Stack: Organized as array of words, that are pushed/popped from.
//      Frame Data: Contains exception table, symbolic, and constant references.
//
// JVM HEAP
//        The java Heap is divided into two main parts:
//        - Young Generation - has "MINOR GC", subdivided into three parts:
//        * Eden - Most of new objects are created. here
//        * Survivor0 - Objects are checked and moved from one to the other survivor space.
//        * Survivor1 - Objects that survive many GC cycles move from survivor space to Old Memory.
//        - Old Memory - has "MAJOR GC", GC runs when full.
//        Objects are created on the heap.
//        Call hierarchy and local variables are stored on stacks.
//        Java Heap dump is a snapshot of the heap at any given time.
//        Garbage collection in the heap is mandatory.
//        The Heap size can only be changed on JVM startup ()NOT dynamically once running).
//
// JVM PERMANENT GENERATION
//        Permanent Generation (a.k.a. Perm Gen) contains the application metadata required
//        by the JVM to describe the classes and methods used in the application.
//        NOTE: The Perm Gen is not part of Java Heap memory.
//        Perm Gen is populated by JVM at runtime based on the classes used by the
//        application, it also contains Java SE library classes and methods.
//        Perm Gen objects ARE garbage collected in a full garbage collection.
//
// GARBAGE COLLECTION
// Garbage Collection tracks each and every object available in the JVM heap space and removes unused objects when they
// become eligible.  This comes at a slight performance cost, or overhead, but removes the need for the user to allocate
// and de-allocating memory.
//
// Objects becomes eligible for GC when there is no live reference for that object, or, it can no longer be reached by
// any live thread. Note that cyclic references do not count as a live reference (i.e., if two objects are pointing to
// each other, neither hav a live reference, then both are eligible for GC).
//
// The object that performs the garbage collection is called a Garbage Collector or GC.  There are four implementations
// of garbage Collector:
//      Serial      Simplest, freezes all application threads when it runs: java -XX:+UseSerialGC -jar Application.java
//      Parallel    A.k.a Throughput Collectors, use multiple threads for managing heap space, also freezes other
//                  application threads while performing GC: java -XX:+UseParallelGC -jar Application.java
//      CMS         A.k.a. Concurrent Mark and Sweep, uses multiple garbage collector threads for GC, has short GC
//                  pauses, but responds slower: java -XX:+UseParNewGC -jar Application.java
//      G1          Garbage First, added in Java 1.7, increases throughput and decreases GC pause time, is the DEFAULT
//                  collector in Java 9: java -XX:+UseG1GC -jar Application.java
//
// JVM FLAGS
//      -X                          Shows all -X options
//      -Xss<size>                  Set java thread stack size
//      -Xmx<size>                  Set maximum memory allocation pool.
//      -Xms<size>                  Set initial memory allocation pool.
//      -Xmn<size>                  Set the initial and maximum size (in bytes) of heap for young generation/nursery.
//      -XX:+UseSerialGC            Set Serial Collector as GC.
//      -XX:+UseParallelGC          Set Parallel Collector as GC.
//      -XX:+UseConcMarkSweepGC     Set CMS (Concurrent Mark and Sweep Collector) as GC.
//      -XX:+UseG1GC                Set G1 Collector as GC.
//      -XX:PermGen<size>           Set initial PermGen size.
//      -XX:MaxPermSize<size>       Set the maximum PermGen size.
//      -XX:SurvivorRatio=<ratio>   Set ratio of Eden space and Survivor space.
//      -XX:NewRatio=<ratio>        Set ratio of old/new generation sizes (default is 2).

class GCReview {
    public static void examples() {
        // NOTE: Garbage Collecting can only be REQUESTED, and not immediately forced, via:
        System.gc();  // Class method, non-native method, in java.lang.System.
        // Or:
        Runtime.getRuntime().gc();  // - Instance method, native method, in java.lang.Runtime.
    }
}



///////////
// JUNIT //
///////////
//
// JUnit is a unit testing framework for the Java programming language. JUnit has been important in the development of
// test-driven development, and is one of a family of unit testing frameworks which is collectively known as xUnit that
// originated with SUnit.
//
// SOME of the differences between JUnit 4 and JUnit 5, aside from the change in architecture from one Jar three
// sub-projects (JUnit Platform, JUnit Jupiter, JUnit Vintage), are listed below:
//       JUnit 4                  JUnit 5
//       -------                  -------
//       JDK 5            -->     JDK 8               Minimum JDK
//       @Test                    @Test               Marks a test method in a class; will be executed/reported.
//       @RunsWith                @RunsWith
//       @Before          -->     @BeforeEach
//       @BeforeClass     -->     @BeforeAll
//       @After           -->     @AfterEach
//       @AfterClass      -->     @AfterAll
//       @Ignore          -->     @Disable
//       @Category        -->     @Tag
//       @Suite           -->     N/A
//       @Rule            -->     N/A
//       N/A              -->     @Nested             Nested tests.
//       N/A              -->     @TestFactory        Creates test cases at runtime; for rand/external data tests.
//       N/A              -->     @ExtendWith         Register custom extensions.
//       N/A              -->     @SelectPackages
//       N/A              -->     @SelectClasses
//       N/A              -->     @DisplayName()      Changes the displayed name of the testing method.
//       N/A              -->     @RepeatedTest()     Repeat the test a number of times.
//       N/A              -->     @TestInstance
//
// JUnit uses assertions to assert conditions in tests; common assertions include:
//      assertEquals()  and assertNotEquals()
//      assertSame()    and assertNotSame()
//      assertFalse()   and assertTrue()
//      assertThrows()
//      assertArrayEquals()
//      assertIterableEquals()
//      assertLinesMatch()
//      assertTimeout()
//      assertTimeoutPreemptively()
//      assertAll()
//
// Assumptions (or a boolean value), can be supplied to some assertions and dictate if that assertion is executed (true)
// or not executed (false).

// The Class TO TEST:
class StringUtils {
    public static Double toDouble(String str) {
        if (str == null) { return null; }
        return Double.valueOf(str);
    }

    public static boolean empty(String str) {
        return str == null || str.trim().length() == 0;
    }

    public static String concat(String... strs) {
        String concatString = null;
        if (strs != null && strs.length > 0) {
            StringBuilder sb = new StringBuilder();
            for (String st : strs) {
                if (st != null) {
                    sb.append(st);
                }
            }
            concatString = sb.toString();
        }
        return concatString;
    }
}

// An EXAMPLE of a matching JUnit test class:
// NOTE: Test classes should be PUBLIC (in their own file), and are usually in a separate test directory from the src
// directory (i.e., project/test/java/com/...).
class StringUtilsTest{
    @BeforeAll
    public static void setup() {
        System.out.println("@BeforeAll annotated methods must be static void, and are good for connecting to servers.");
    }

    @BeforeEach
    public void before() {
        System.out.println("@BeforeEach is useful for executing common code before tests.");
    }

    @Test
    public void toDouble() {
        // Valid string test.
        String validValue = "1969";
        final Double validExpVal = Double.valueOf(validValue);
        final Double validActual = StringUtils.toDouble(validValue);

        assertAll("Multiple Assertions.", () -> {
            assertNotNull(validActual);
            assertEquals(validExpVal, validActual);
        });

        // Test null string.
        final String nullString = null;
        final Double nullStringActual = StringUtils.toDouble(nullString);
        assertNull(nullStringActual, "The actual is not null");

        // Test non-numeric string.
        final String naString = "N/A";
        assertThrows(NumberFormatException.class, () -> { StringUtils.toDouble(naString); });

    }

    @DisplayName("Repeated Test")
    @RepeatedTest(value = 5, name = "{displayName} -> {currentRepetition} of {totalRepetitions}")
    public void empty() {
        // Test the case that the input is NULL
        String input = null;
        assertTrue(StringUtils.empty(input));

        // Test white space.
        input = " ";
        assertTrue(StringUtils.empty(input));

        // Test case with the input is not empty
        input = "not empty...";
        assertFalse(StringUtils.empty(input));
    }

    @Test
    public void concat() {
        // Test with three strings.
        String st1 = "Hello", st2 = "World", st3 = "!";
        String expect = st1 + st2 + st3;
        String actual = StringUtils.concat(st1, st2, st3);
        assertEquals(expect, actual);

        // Test with null.
        st3 = null;
        assertEquals(st1 + st2, StringUtils.concat(st1, st2, st3));
    }

    @Disabled
    @Test
    public void concatWithAllNullInputTest() {
        assertNull(StringUtils.concat());
    }

    @AfterEach
    public void after() {
        System.out.println("@AfterEach will run after each test.");
    }

    @AfterAll
    public static void tearDown() {
        System.out.println("@AfterAll annotated methods must be static void, and are good for disconnecting from servers.");
    }
}


////////////////////////
// MISCELLANEOUS JAVA //
////////////////////////

class MiscellaneousJava{
    public void snippets(){

        // Show memory usage:
        System.out.println("KB: " + (double) (Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory()) / 1024);

        try {
            InetAddress localHost = InetAddress.getLocalHost();

            InetAddress inet = InetAddress.getByAddress(new byte[]{127, 0, 0, 1});
            System.out.println(inet.isReachable(5000) ? "Host is reachable" : "Host is NOT reachable");

            //  How to get the IP from a Hostname (cached):
            InetAddress address = InetAddress.getByName("www.yahoo.com");
            System.out.println(address.getHostAddress());

            // How to get Hostname from IP:
            InetAddress addr = InetAddress.getByName("192.168.0.1");
        }catch(IOException e){
            System.out.println("Caught exception:" + e.toString());
        }

        // Date and Time (one-liner):
        String timeStamp = new SimpleDateFormat("yyyyMMddHHmmss").format(Calendar.getInstance().getTime());

        // Date and Time (multi-line) via Calendar:
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Calendar cal = Calendar.getInstance();
        System.out.println(dateFormat.format(cal.getTime()));

        // Date and Time (multi-line) via Date:
        DateFormat dateFormat0 = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Date date = new Date();
        System.out.println(dateFormat0.format(date));

        // How to suppress warnings:
        @SuppressWarnings({ "null", "unused" })
        String nullString = null;
    }
}

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package com.mpettersson.review;

import org.junit.jupiter.api.*;

import org.junit.jupiter.api.Test;

import java.io.*;

import java.net.InetAddress;

import java.nio.file.*;

import java.text.DateFormat;

import java.text.SimpleDateFormat;

import java.util.*;

import java.util.concurrent.*;

import java.util.concurrent.locks.Lock;

import java.util.concurrent.locks.ReentrantLock;

import java.util.function.*;

import java.util.regex.Pattern;

import java.util.stream.Collectors;

import java.util.stream.Stream;

import static org.junit.jupiter.api.Assertions.*;

public class Java {

// Enums

public enum Day {Monday, Tuesday, Wednesday};

public static void main(String[] args) {

// Single line comment

/**

* Multi line comment, used by javadocs (documentation)

Multi line comment

////////////////////////

// NAMING CONVENTIONS //

////////////////////////

/**

* PACKAGES

* - Always lowercase

* - Should be unique

* - Use your internet domain name reversed as prefix for package.

* - Replace invalid characters with underscore (_), i.e., experts-exchange.com --> com.experts_exchange

* - Domain name components starting with a number should start with an underscore (_), i.e., 1world.com --> com._1world

* - Domain name components that are java key words should start with an underscore (_), i.e., switch.supplier.com --> com.supplier._switch

* CLASSES

* - CamelCase

* - Should start with a capital letter

* - Each word in the name should also start with a capital letter.

* - Should be a nouns.

* INTERFACES

* - CamelCase

* - Should start with a capital letter.

* - Each word in the name should also start with a capital letter.

* - Can start with I (old convention)

* METHODS

* - MixedCase

* - Should start with a lowercase letter.

* - Each word in the name should start with a capital letter.

* - Often Verbs

* CONSTANTS

* - All upper case.

* - Separate words with an underscore (_)

* - Declare using the final keyword.

* VARIABLES

* - MixedCase

* - Should start with a lowercase letter.

* - Each word in the name should start with a capital letter.

* - No underscores (_).

* TYPE PARAMETERS

* - Single Capital Letter.

* - examples:

* E - Element

* K - Key

* V - Value

* S, U, V, etc. - 2nd, 3rd, 4th types.

* ? - Is the Unknown Type.

////////////////////////////

// 8 PRIMITIVE DATA TYPES //

////////////////////////////

// null is case sensitive in java, i.e., you CAN'T use NULL!

// final variables can't be changed once initialized (can declare and define/initalize in two different lines).

// Multiple variables of the same type can declared and assigned at once: int a = 10, b = 11, c = 12;

// BYTE - 8 bits

final byte myMinByte = -128;

byte myMaxByte = 127;

byte byteCastExample = (byte) (myMinByte / 2); // How to cast.

// SHORT - 16 bits

short myMinShort = -32768;

short myMaxShort = 32767;

// INT - 32 bits

int myMinInt = -2_147_483_648; // You can use underscores now...

int myMaxInt = 2_147_483_647;

// LONG - 64 bits

long myMinLong = -9_223_372_036_854_775_808L; // Need to put a 'L' or 'l' behind it.

long myMaxLong = 9_223_372_036_854_775_807L; // NOTE there isn't anything for short or byte.

// FLOAT - 32 BITS - 7 decial digit percision

float myFloatValue = 5F / 3f; // Should cast or use either 'F' or 'f' for float

System.out.println("myFloatValue: " + myFloatValue);

// DOUBLE - 64 BITS - has 16 decial digit percision

// NOTE: USE DOUBLE OVER FLOAT, double is usually faster on modern computers and many of java's functions use it

double myDoubleValue = 5d / 3D; // Should cast or use either 'D' or 'd' for double

double pi = 3.141_592_7d; // can use literals in numbers in java 7 or greater

System.out.println("myDoubleValue: " + myDoubleValue);

// CHAR - 16 bits, can be unicode or ASCII, remember there is only 128 ASCII...

char myChar = '#'; // has to use single quotes.

char copyrightChar = '\u00a9'; // can be unicode

System.out.println("Unicode copyright char: '\\u00a9' = " + copyrightChar);

System.out.println("ASCII to char: (char)42 = " + (char)42);

System.out.println("Char to ASCII: (int)'*' = " + (int)'*');

// BOOLEAN - No defined size

boolean myBoolean = true;

// boolean from string:

boolean trueFlag = Boolean.valueOf("true");

boolean falseFlag = Boolean.valueOf("false");

// Primitive Type Values:

System.out.println("Byte.TYPE: " + Byte.TYPE);

System.out.println("Byte.SIZE: " + Byte.SIZE);

System.out.println("Byte.MIN_VALUE: " + Byte.MIN_VALUE);

System.out.println("Byte.MAX_VALUE: " + Byte.MAX_VALUE);

System.out.println("Short.TYPE: " + Short.TYPE);

System.out.println("Short.SIZE: " + Short.SIZE);

System.out.println("Short.MIN_VALUE: " + Short.MIN_VALUE);

System.out.println("Short.MAX_VALUE: " + Short.MAX_VALUE);

System.out.println("Integer.TYPE: " + Integer.TYPE);

System.out.println("Integer.SIZE: " + Integer.SIZE);

System.out.println("Integer.MIN_VALUE: "+ Integer.MIN_VALUE);

System.out.println("Integer.MAX_VALUE: "+ Integer.MAX_VALUE);

System.out.println("Long.TYPE: " + Long.TYPE);

System.out.println("Long.SIZE: " + Long.SIZE);

System.out.println("Long.MIN_VALUE: " + Long.MIN_VALUE);

System.out.println("Long.MAX_VALUE: " + Long.MAX_VALUE);

System.out.println("Float.TYPE: " + Float.TYPE);

System.out.println("Float.SIZE: " + Float.SIZE);

System.out.println("Float.MIN_VALUE: " + Float.MIN_VALUE);

System.out.println("Float.MAX_VALUE: " + Float.MAX_VALUE);

System.out.println("Double.TYPE: " + Double.TYPE);

System.out.println("Double.SIZE: " + Double.SIZE);

System.out.println("Double.MIN_VALUE: " + Double.MIN_VALUE);

System.out.println("Double.MAX_VALUE: " + Double.MAX_VALUE);

System.out.println("Boolean.TYPE: " + Boolean.TYPE);

System.out.println("Character.TYPE: " + Character.TYPE);

System.out.println("Character.SIZE: " + Character.SIZE);

System.out.println("(int) Character.MIN_VALUE): " + (int) Character.MIN_VALUE);

System.out.println("(int) Character.MAX_VALUE): " + (int) Character.MAX_VALUE);

// Common Math Functions

int x = 10, y = 100;

double d = 1.0 / 3.0;

System.out.println("Math.max(" + x + ", " + y + "): " + Math.max(x, y));

System.out.println("Math.min(" + x + ", " + y + "): " + Math.min(x, y));

System.out.println("Math.pow(" + x + ", " + y + "): " + Math.pow(x, y));

System.out.println("Math.floorDiv(" + x + ", " + y + "): " + Math.floorDiv(x, y));

System.out.println("Math.floorMod(" + x + ", " + y + "): " + Math.floorMod(x, y));

System.out.println("Math.sqrt(" + x + "): " + Math.sqrt(x));

System.out.println("Math.log(" + x + "): " + Math.log(x));

System.out.println("Math.floor(" + d + "): " + Math.floor(d));

System.out.println("Math.ceil(" + d + "): " + Math.ceil(d));

System.out.println("Math.abs(" + x + "): " + Math.abs(x));

System.out.println("Math.random():" + Math.random()); // Returns double >= 0.0 and < 1.0

// How to get random values:

System.out.println("Math.random():" + Math.random()); // Returns double >= 0.0 and < 1.0

int bound = 10;

int seed = 100;

byte[] bytes = new byte[10];

Random random = new Random();

random.nextInt(); // Returns int >= Integer.MIN_VALUE and <= Integer.MAX_VALUE

random.nextInt(bound); // Returns int >=0 < bound, ONLY int can have bound.

random.nextDouble(); // Returns double >= 0.0 and < 1.0

random.nextBytes(bytes); // Puts random bytes into each index of supplied array.

random.nextBoolean();

random.setSeed(seed);

System.out.println("random.nextInt(): " + random.nextInt());

System.out.println("random.nextInt(" + bound + "): " + random.nextInt(bound));

System.out.println("random.nextDouble(): " + random.nextDouble());

System.out.println("random.nextBytes(bytes): " + Arrays.toString(bytes));

System.out.println("random.nextBoolean(): " + random.nextBoolean());

System.out.println("random.setSeed(" + seed + ")");

// COMPARETO

// NOTE: The object type must extend Comparable, i.e., class MyObject<T extends Comparable>

// Can't be primitive types (so use Integer for int, Double for double, etc...)

// Usage:

// myObjectLeft<T>.compareTo(myObjectRight<T>)

// Results:

// 0 if myObjectLeft == myObjectRight

// -1 if myObjectLeft < myObjectRight (it's -1 no matter size i.e., 1 < 2 or 1 < 2222)

// 1 if myObjectLeft > myObjectRight (it's 1 no matter size i.e., 2 > 1 or 2222 > 1)

Integer one = 1;

Integer negOne = -1;

Integer six = 6;

System.out.println(one + ".compareTo(" + one + ")" + one.compareTo(one)); // 1.compareTo(1) == 0 (1 == 1)

System.out.println(one + ".compareTo(" + six + ")" + one.compareTo(six)); // 1.compareTo(6) == -1 (1 < 6)

System.out.println(six + ".compareTo(" + one + ")" + six.compareTo(one)); // 6.compareTo(1) == 1 (6 > 1)

System.out.println(one + ".compareTo(" + negOne + ")" + six.compareTo(negOne)); // 6.compareTo(-1) == 1 (6 > -1)

/////////////

// STRINGS //

/////////////

// Strings are a class/Object and not a primitive type.

String myString = "This is my string!";

String strHello = "Hello";

String strWorld = "World";

String eol = System.lineSeparator();

// Concat with

System.out.println(strHello + strWorld); // This will automatically convert to string

System.out.println(strHello.concat(strWorld)); // This WILL NOT automatically convert to string!!!

// NOTE: You can assign null to a string, BUT, it'll cause exceptions with many of the common string ops.

String nullString = null;

System.out.println(nullString);

String emptyString = "";

// Find string length with <stringVar>.length();

System.out.println("emptyString.length() = " + emptyString.length());

// Find if string is empty (i.e., length == 0) with <stringVar>.isEmpty();

System.out.println("emptyString.isEmpty() = " + emptyString.isEmpty());

String example = "This should be complicated enough to show some things we should show";

// Find the characters at the indexes given

System.out.println(example.charAt(0));

System.out.println(example.charAt(5));

// An StringIndexOutOfBoundsException is thrown in both these cases:

// System.out.println(example.charAt(-1));

// System.out.println(example.charAt(200));

// Find the index of characters or substrings

System.out.println(example.indexOf('s')); // returns the first occurence of 's'

System.out.println(example.indexOf('s', 4)); // the first 's' after index 4

System.out.println(example.indexOf("should")); // the index of the first "should" in our string

System.out.println(example.indexOf("should", 15)); // the index of the first "should" in our

// Find the last index of characters or substrings

System.out.println(example.lastIndexOf('s')); // returns the first occurence of 's' when we look backwards from the end of the string

System.out.println(example.lastIndexOf('s', 45)); // searches for 's' backwards from the position 45

System.out.println(example.lastIndexOf("should")); // returns the position at which the substring 'should' appears, looking backwards from the end of the string

System.out.println(example.lastIndexOf("should", 20)); // finds substring 'should' from position 20 backwards, and returns the position at which it begins

// The compareTo() method compares the Unicode value of two strings and returns a NUMBER.

System.out.println("a".compareTo("a"));

System.out.println("a".compareTo("b"));

System.out.println("1".compareTo("12345678"));

// Get substrings with substring() method.

System.out.println(example.substring(2));

System.out.println(example.substring(5,11));

// Trim off the leading and trailing whitespace with .trim()

String ourString = " Any non-leading and non-trailing whitespace is \n preserved ";

System.out.println(ourString.trim());

// Printf: formatted output

// %s : strings

// %d : Integers

// %f : Floats/Doubles

// %c : Characters

// %e : Scientific Notation

// %t : Dates

// %b : Booleans

// %o : Octal

// %h : Hex

// The format syntax is: %[argument_index$][flags][width][.precision]conversion

double ourDouble = 1123.9303;

System.out.println(String.format("%f", ourDouble));

System.out.println(String.format("%.3f", ourDouble)); // specifies that we only want 3 digits after decimal point

System.out.println(String.format("%e", ourDouble));

String formatString = "what does precision do with strings?";

System.out.println(String.format("%.8s", formatString)); // prints the first 8 characters of our string

int ourInt = 123456789;

// System.out.println(String.format("%.4d", ourInt)); // precision can't be used on ints

// If our number has less than 6 digits, this will add extra 0s to the beginning until it does

System.out.println(String.format("%06d", 12));

// If our number has more than 6 digits, it will just print it out

System.out.println(String.format("%06d", 1234567));

// We can specify output width, with the output being aligned to the right if it's shorter than the given space. If it's

// longer, everything gets printed. The || are added for demonstration purposes only

System.out.println(String.format("|%20d|", 12));

// Or we can align the output to the left

System.out.println(String.format("|%-20d|", 12));

// We can also easily print an octal/hexadecimal value of an integer

System.out.println(String.format("Octal: %o, Hex: %x", 10, 10));

String replaceString = "We really don't like the letter e here";

System.out.println(replaceString.replace('e', 'a'));

System.out.println(replaceString.replace("here", "there"));

System.out.println(replaceString.replaceAll("e(r+)", "a"));

System.out.println(replaceString.replaceFirst("e(r+)", "a"));

// How to split a string using regex:

String[] fruits = "apples, oranges, pears, pineapples".split(",");

System.out.println(Arrays.toString(fruits));

// Using trim() to clean up some of the items.

for(int i = 0; i < fruits.length; i++) {

fruits[i] = fruits[i].trim();

}

System.out.println(Arrays.toString(fruits)); // Arrays.toString() formats the output array on its own

// This returns then prints an empty array, since every character is interpreted as something to be split at and ignored

System.out.println(Arrays.toString("apples.oranges.pears.pineapples".split(".")));

// The "regex safe" way of doing this would be

System.out.println(Arrays.toString("apples.oranges.pears.pineapples".split(Pattern.quote("."))));

// Splits our string to two substrings at most, completely ignoring all other occurrences of "."

System.out.println(Arrays.toString("apples.oranges.pears.pineapples".split(Pattern.quote("."), 2)));

// Split strings at new lines:

String lines[] = myString.split("[\\r\\n]+");

// Split strings at spaces:

String spaces[] = myString.split("\\s+");

// examples of String.join()

String arrayOfStrings[] = {"1","2","3","4","5"};

System.out.println(String.join("-", arrayOfStrings));

System.out.println(String.join("-", Arrays.asList(arrayOfStrings))); // Works just fine with lists as well

System.out.println(String.join("", arrayOfStrings));

// How to convert a string to a char aray:

System.out.println(Arrays.toString("How to convert a string to a Char Array".toCharArray()));

// SORT STRING - No method to sort a string, but can do this:

String stringToSort = "Hahaha, Sort ME!";

char[] chars = stringToSort.toCharArray();

Arrays.sort(chars);

String sortedString = new String(chars);

System.out.println(sortedString);

// How to remove all whitespaces (and newlines) from a string:

String strWithWhiteSpaces = " S\ttring wit h white spa\n c e s !!! ";

System.out.println(strWithWhiteSpaces);

System.out.println(strWithWhiteSpaces.replaceAll("\\s+", ""));

//////////////////////////////////

// STRINGBUILDER & STRINGBUFFER //

//////////////////////////////////

// StringBuffer - First, Thread Safe/Synchronized

// StringBuilder - Second, NOT Thread Safe, Several times FASTER

StringBuilder strBuilder = new StringBuilder("A Random Value");

// How to check the current capacity

System.out.println(strBuilder.capacity());

// Get the length of the used string with .length()

System.out.println(strBuilder.length());

// Append

// NOTE: It will automatically add to the capacity if needed.

System.out.println(strBuilder.append(" Again And Again And Again And Again And Again And Again And Again"));

// Replace

System.out.println(strBuilder.replace(2, 7,"NONRANDOM"));

// Delete:

System.out.println(strBuilder.delete(15, 21));

// Insert:

System.out.println(strBuilder.insert(30, "String To Insert"));

// Reverse:

System.out.println(strBuilder.reverse());

// Print:

System.out.println(strBuilder);

// Use this to assign to a string

System.out.println(strBuilder.toString());

///////////

// INPUT //

///////////

// // Scanner Example:

// Scanner sc = new Scanner(System.in);

// System.out.print("Enter name: ");

// if(sc.hasNextLine()){

// String userName = sc.nextLine();

// System.out.println("Hello " + userName);

// }

// // Scanner Example with different types:

// Scanner scanner = new Scanner(System.in);

// System.out.println("Enter your name: ");

// String name = scanner.nextLine();

// System.out.println("Your name is: " + name);

// System.out.println("Enter your year of birth: ");

// int year = scanner.nextInt();

// NOTE YOU HAVE TO CALL scanner.nextLine() to handle the newline (enter) if you want to do nextLine() for a string.

// scanner.nextLine();

// System.out.println("Your age is: " + (2018 - year));

// scanner.close();

// // JOPtion Pane Dialog Box Example:

// String jopName = JOptionPane.showInputDialog("Enter name");

// System.out.println("Hello " + jopName);

/////////////////////////////

// CONTROL FLOW STATEMENTS //

/////////////////////////////

int someVar = 4;

// Remember that assignment returns the value assigned, so it has some weird cases...

if((someVar = 10) == 10){

System.out.println("what");

}

boolean blah;

if(blah = true){

System.out.println("this is the 'if' with an assignment.");

}

// NOTE: Unlike other languages (python, C/C++, etc.) numbers cannot be used in place of booleans.

// The following (commented out code), has an error ('Incompatible Types'):

// if(1){ System.out.println("True"); }

// Whitespace and indenting stuff...

int anothervar=5;

System.out.println(anothervar);

int

anotherMessedUp

;

System.out.println(anotherMessedUp);

String mySwitchString = "matt";

switch(mySwitchString){

case "matt":

System.out.println("input was matt");

break;

case "no":

System.out.println("input was no");

break;

default:

System.out.println("blah");

}

// Can use byte, short, char, int, and Strings with switch statements.

int switchValue = 1;

switch(switchValue){

case 1:

System.out.println("Value was 1");

break;

case 2:

System.out.println("Value was 2");

break;

case 3: case 4: case 5: // How to have multiple values in a case.

System.out.println("Value was 3, 4, or 5.");

default:

System.out.println("In default case...");

break; // Don't really need a break here, but it's probably good to add it.

}

int count = 1;

while(count != 6){

System.out.println("count value is " + count);

count++;

}

for(int i = 6; i !=6; i++){

System.out.println("count value is " + count);

}

count = 1;

do{

System.out.println("count value is " + count);

if(count > 100){

break;

}

count++;

}while(count != 6);

String numberAsString = "2018";

int intNumber = Integer.parseInt(numberAsString);

double doubleNumber = Double.parseDouble(numberAsString);

System.out.printf("This is the value for intNumber: %d and this is the value for doubleNumber: %f.\n", intNumber, doubleNumber);

////////////

// ARRAYS //

////////////

System.out.println("\nArrays Examples");

// PRIMITIVE ARRAYS:

int[] myIntArray1 = new int[3];

int[] myIntArray2 = {1, 2, 3};

int[] myIntArray3 = new int[]{1, 2, 3};

// CLASS/STRING ARRAYS:

String[] myStringArray1 = new String[3];

String[] myStringArray2 = {"a", "b", "c"};

String[] myStringArray3 = new String[]{"a", "b", "c"};

//Declare and Initialize in separate statements:

String[] myStringArray4;

myStringArray4 = new String[]{"a", "b", "c"}; // The cast is necessary.

// Multidimentional

int[][] multiDimArray = {{1,2}, {1,2}, {1,2}, {1,2}, {1,2}};

// How to copy arrays:

// NOTE: Anything other than primitive data types will have shallow copies.

int a1[] = {1,2,3};

int a2[] = Arrays.copyOf(a1, 3);

System.out.println(a2[0] + " " + a2[1] + " " + a2[2]);

// How to sort an Array:

int a3[] = {8, 7, 5, 2, 1};

Arrays.sort(a3);

// How to print an Array:

System.out.println("Arrays.toString(a3): " + Arrays.toString(a3));

////////////////////////////

// COLLECTION (INTERFACE) //

////////////////////////////

// A collection represents a group of objects, known as its elements. The Collection interface is the root

// interface in the collection hierarchy, that is, List Set and Queue interfaces extend the Collection interface.

// Although the Map interface does not extend/implement the Collection interface (because Map hash key value

// paris), it is considered part of the Collections Framework.

// The Collection interface is in the java.util package, some of it's more important methods include size(),

// isEmpty(), contains(), iterator(), toArray(), add(E e) , remove(), clear(), equals(), and hashCode().

// The four major data structure types in the Collections Framework are List, Set, Queue, and Map.

// LIST

// Lists are ordered collections (sequences) of items that are accessed via an integer index, and typically

// allow duplicate values. The following are implemented List classes:

// Vector - Synchronized, growable array of objects accessed via an int index.

// Stack - Synchronized, Last-In-First-Out (LIFO) stack of objects (extends Vector).

// ArrayList - NOT synchronized, resizeable array implementation of List, allows nulls.

// LinkedList - NOT synchronized, doubly-linked list implementation (extends AbstractSequentialList).

// SET

// Sets are collections that do not allow duplicate elements, and model the mathematical set abstraction. The

// following are implemented Set classes:

// HashSet - NOT synchronized, Set implementation by HashMap, allows one null, NOT ordered.

// LinkedHashSet - NOT synchronized, Hashtable & LinkedList imp of Set, ordered via doubly-linked list.

// TreeSet - Not synchronized, NavigableSet implementation based on HashMap, allows one null, NOT ordered.

// QUEUE

// Queues are "a collection designed for holding elements prior to processing". Queues typically, but do not

// necessarily, order elements in a FIFO (first-in-first-out) manner. Among the exceptions are priority queues,

// which order elements according to a supplied comparator, or the elements' natural ordering, and LIFO queues

// (or stacks) which order the elements LIFO (last-in-first-out). The implemented Queue classes are:

// ArrayDequeue - NOT synchronized, resizable-array imp of the Deque interface, nulls NOT allowed.

// PriorityQueue - NOT synchronized, unbounded priority queue (First-In-First-Out) based on a priority heap.

// NOTE: LinkedList implements Dequeue.

// MAP

// A Map is an object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most

// one value. The Map interface is interesting in that it does not implement or extend any other class.

// Implemented Map classes include:

// HashMap - NOT synchronized, Hashtable based imp of Map, allows null vals and 1 null key, no order guarantees.

// Hashtable - Synchronized, Hashtable imp of Map, null NOT allowed, NOT ordered.

// TreeMap - NOT synchronized, Red-Black tree based NavigableMap imp; (ordered) SORTED by keys.

// LinkedHashMap - NOT synchronized, HashTable & LinkedList imp of the Map interface, ordered via dlinkedlist.

// IdentityHashMap - NOT synchronized, HashTable based Map imp using reference-equality when comparing keys.

// To iterate over a collection, without modifying it, use the for-each loop (for(Element e: collection)...).

// To iterate over and access collection elements use; Enumeration, Iterator, and ListIterator.

// ENUMERATION

// The Enumeration Interface was the first iterator, present in JDK 1.0, and only works on legacy collections

// (Vector and Hashtable). Only three methods were provided; hasMoreElements(), nextElement(), and asIterator().

// It can only iterate in a forward direction (and can't Remove/Add/Set elements).

// ITERATOR

// Added in Java 1.2, "Iterator takes the place of Enumeration in the Java Collections Framework". Iterators can

// read and remove elements on ALL Collection objects. Iterator methods include: hasNext(), next(), remove, and

// forEachRemaining().

// LISTITERATOR

// ListIterator extends Iterator, is ONLY available to lists (only AbstractList implements it), allows for

// Bi-Directional movement, and can add/remove/set elements. ListIterator has hasNext(), next(), hasPrevious(),

// previous(), nextIndex(), previousIndex(), remove(), set(E e) and add(E e) methods.

// NOTE: ListIterator has no "current" element, that it always lies between the element that would be returned

// by a previous() call and the element that would be returned by a next() call, furthermore, the remove() and

// set(E e) methods act on the last element returned by next()/previous().

///////////////////

// VECTOR (LIST) //

///////////////////

// IS Synchronized

System.out.println("\nVector Example");

// NOTE: You have to use Uppercase Integer here BC it needs classes not primitives.

Vector<Integer> vector = new Vector<>();

vector.add(0); // Add 0 (at END) -- Autoboxing will auto-convert int to Integer

vector.add(Integer.valueOf(1)); // Add 1 (at END) -- So don't have to do Integer.valueOf()...

vector.add(2); // Add 1 (at END)

vector.add(2, 99); // Add 99 at index 2

vector.add(0, -0); // Add -0 at index 0

vector.addAll(Arrays.asList(5,6,7,8)); // Add all elements of a collection.

vector.set(2, 22); // Set value at index 2 to 22

vector.get(2); // Return value at index 2 -- Autoboxing will convert Integer to int.

vector.get(0).intValue(); // Return value at index 0 -- So don't need to use intValue().

for(Integer i: vector){/* do stuff */} // Iterate Via Enhanced For Loop

Iterator vectorIt = vector.iterator(); // Iterate Via ITERATOR

while (vectorIt.hasNext()){vectorIt.next();} // And hasNext() method.

Object[] vectorObjArray = vector.toArray(); // How to convert a Vector to an Object Array:

System.out.println("vector.toString(): " + vector.toString());

System.out.println("vector.get(2): " + vector.get(2));

System.out.println("vector.indexOf(0): " + vector.indexOf(0));

System.out.println("vector.lastIndexOf(0): " + vector.lastIndexOf(0));

System.out.println("vector.lastElement(): " + vector.lastElement());

System.out.println("vector.isEmpty(): " + vector.isEmpty());

System.out.println("vector.contains(2): " + vector.contains(2));

System.out.println("vector.capacity(): " + vector.capacity());

System.out.println("vector.size(): " + vector.size());

vector.remove(0); // Remove and return item in index 0

vector.remove((Object) 2); // Remove object matching 2 (no exception if no match).

vector.clear();

//////////////////

// STACK (LIST) //

//////////////////

// Extends Vector.

System.out.println("\nStack Example");

Stack<Integer> stack = new Stack<>();

stack.push(0); // Push 0 on stack (or end if viewed as list).

for(int i = 1; i < 5; i++) { stack.push(i); }

stack.add(99); // Add 99 to top of stack (or end if viewed as list).

stack.addAll(Arrays.asList(5,6,7,8)); // Add all of a collection to stack.

stack.set(2, 22); // Set value at index 2 to 22

stack.get(2); // Return value at index 2

for(Integer i: stack){/* do stuff */} // Iterate Via Enhanced For Loop

Iterator stackIt = stack.iterator(); // Iterate Via ITERATOR

while (stackIt.hasNext()){stackIt.next();} // And hasNext() method.

Object[] stackObjArray = stack.toArray(); // How to convert to an Object Array:

System.out.println("stack.get(2): " + stack.toString());

System.out.println("stack.get(2): " + stack.get(2));

System.out.println("stack.size(): " + stack.size());

System.out.println("stack.search(2): " + stack.search(2));

System.out.println("stack.peek(): " + stack.peek());

System.out.println("stack.empty(): " + stack.empty());

System.out.println("stack.pop(): " + stack.pop());

stack.pop();

stack.remove(0); // Remove and return item in index 0

stack.remove((Object) 2); // Remove object matching 2 (no exception if no match).

stack.clear();

//////////////////////

// ARRAYLIST (LIST) //

//////////////////////

System.out.println("\nArrayList Example");

ArrayList<Integer> arrayList = new ArrayList<>();

arrayList.add(0); // Add 0 (at tail)

arrayList.add(Integer.valueOf(1)); // Add 1 (at tail)

arrayList.add(2); // Add 1 (at tail)

arrayList.add(2, 99); // Add 99 at index 2

arrayList.add(0, -0); // Add -0 at index 0

arrayList.addAll(Arrays.asList(5,6,7,8)); // Add all of a collection.

arrayList.set(2, 22); // Set value at index 2 to 22

arrayList.get(2); // Return value at index 2

arrayList.get(0).intValue(); // Return value at index 0

for(Integer i: arrayList){/* do stuff */} // Iterate Via Enhanced For Loop

Iterator arrayListIt = arrayList.iterator(); // Iterate Via ITERATOR

while (arrayListIt.hasNext()){arrayListIt.next();} // And hasNext() method.

Object[] arrayListObjArray = arrayList.toArray(); // How to convert to an Object Array:

System.out.println("arrayList.toString(): " + arrayList.toString());

System.out.println("arrayList.get(2): " + arrayList.get(2));

System.out.println("arrayList.indexOf(0): " + arrayList.indexOf(0));

System.out.println("arrayList.lastIndexOf(0): " + arrayList.lastIndexOf(0));

System.out.println("arrayList.isEmpty(): " + arrayList.isEmpty());

System.out.println("arrayList.contains(2): " + arrayList.contains(2));

System.out.println("arrayList.size(): " + arrayList.size());

arrayList.remove(0); // Remove and return item in index 0

arrayList.remove((Object) 2); // Remove object matching 2 (no exception if no match).

arrayList.clear();

///////////////////////////////

// LINKEDLIST (LIST & QUEUE) //

///////////////////////////////

System.out.println("\nLinkedList Example");

LinkedList<Integer> linkedList = new LinkedList<>();

linkedList.add(0); // Add 0 (at tail)

linkedList.add(Integer.valueOf(1)); // Add 1 (at tail)

linkedList.add(2); // Add 1 (at tail)

linkedList.add(2, 99); // Add 99 at index 2

linkedList.add(0, -0); // Add -0 at index 0

linkedList.addFirst(0); // Add 0 to head of linkedList

linkedList.addLast(99); // Add 99 to tail of linkedList

linkedList.addAll(Arrays.asList(5,6,7,8)); // Add all of a collection to stack.

linkedList.set(2, 22); // Set value at index 2 to 22

linkedList.get(2); // Return value at index 2.

linkedList.get(0).intValue(); // Return value at index 0.

linkedList.getFirst(); // Return value at index 0.

linkedList.getLast(); // Return value at last index.

for(Integer i: linkedList){/* do stuff */} // Iterate Via Enhanced For Loop

Iterator linkedListIt = linkedList.iterator(); // Iterate Via ITERATOR

while (linkedListIt.hasNext()){linkedListIt.next();} // And hasNext() method.

Object[] linkedListObjArray = linkedList.toArray(); // How to convert to an Object Array:

System.out.println("linkedList.toString(): " + linkedList.toString());

System.out.println("linkedList.get(2): " + linkedList.get(2));

System.out.println("linkedList.getFirst(): " + linkedList.getFirst());

System.out.println("linkedList.getLast(): " + linkedList.getLast());

System.out.println("linkedList.indexOf(0): " + linkedList.indexOf(0));

System.out.println("linkedList.lastIndexOf(0): " + linkedList.lastIndexOf(0));

System.out.println("linkedList.isEmpty(): " + linkedList.isEmpty());

System.out.println("linkedList.contains(2): " + linkedList.contains(2));

System.out.println("linkedList.size(): " + linkedList.size());

linkedList.remove(0); // Remove and return item in index 0

linkedList.remove((Object) 2); // Remove object matching 2 (no exception if no match).

linkedList.removeFirst();

linkedList.removeFirstOccurrence(0);

linkedList.removeLast();

linkedList.removeLastOccurrence(0);

linkedList.clear();

//////////////////////////

// ARRAYDEQUEUE (QUEUE) //

//////////////////////////

// Poll/Element/Offer are the same as

// Remove/Peek/Add except Remove/Peek throw Exceptions if there is no object.

System.out.println("\nArrayDeque Example");

ArrayDeque<Integer> arrayDeque = new ArrayDeque<>();

arrayDeque.push(0); // Push 0 to head

arrayDeque.add(0); // Add 0 (to tail)

arrayDeque.add(2); // Add 1 (to tail)

arrayDeque.addFirst(0); // Add 0 to head

arrayDeque.addLast(99); // Add 99 to tail

arrayDeque.addAll(Arrays.asList(5,6,7,8)); // Add all of a collection.

arrayDeque.offer(99); // Add 99 to end.

arrayDeque.offerFirst(-0); // Add -0 at head

arrayDeque.offerLast(-9); // Add -0 at tail

arrayDeque.getFirst(); // Return value at index 0.

arrayDeque.getLast(); // Return value at last index.

arrayDeque.peek(); // Return (but doesn't remove) head.

arrayDeque.element(); // Return (but doesn't remove) head.

for(Integer i: arrayDeque){/* do stuff */} // Iterate Via Enhanced For Loop

Iterator arrayDequeueIt = arrayDeque.iterator(); // Iterate Via ITERATOR

while (arrayDequeueIt.hasNext()){arrayDequeueIt.next();} // And hasNext() method.

Object[] ArrayDequeueObjArray = arrayDeque.toArray(); // How to convert to an Object Array:

System.out.println("arrayDeque.toString(): " + arrayDeque.toString());

System.out.println("arrayDeque.peek(): " + arrayDeque.peek());

System.out.println("arrayDeque.element(): " + arrayDeque.element());

System.out.println("arrayDeque.getFirst(): " + arrayDeque.getFirst());

System.out.println("arrayDeque.getLast(): " + arrayDeque.getLast());

System.out.println("arrayDeque.lastIndexOf(0): " + arrayDeque.pollFirst());

System.out.println("arrayDeque.isEmpty(): " + arrayDeque.isEmpty());

System.out.println("arrayDeque.contains(2): " + arrayDeque.contains(2));

System.out.println("arrayDeque.size(): " + arrayDeque.size());

arrayDeque.pop();

arrayDeque.remove(0); // Remove and return item in index 0

arrayDeque.remove((Object) 2); // Remove object matching 2 (no exception if no match).

arrayDeque.removeFirst();

arrayDeque.removeFirstOccurrence(0);

arrayDeque.removeLast();

arrayDeque.removeLastOccurrence(0);

arrayDeque.clear();

///////////////////////////

// PRIORITYQUEUE (QUEUE) //

///////////////////////////

// null values are NOT allowed.

// Objects must be comparable.

// Head of the queue is has lowest priority.

// PriorityQueue Constructor Options:

// PriorityQueue() Uses default initial capacity (11) and natural ordering.

// PriorityQueue(Collection<E> c) Creates PriorityQueue with elements in the specified collection.

// PriorityQueue(int initialCapacity) Uses specified initial capacity and natural ordering.

// PriorityQueue(int i, Comparator<E> c) Uses specified init capacity (i) and uses comparator (c) for order.

// PriorityQueue(PriorityQueue<E> c) Creates a PriorityQueue with ele in the specified priority queue.

// PriorityQueue(SortedSet<E> c) Creates a PriorityQueue with elements in the specified sorted set.

// Poll/Element/Offer are the same as

// Remove/Peek/Add except Remove/Peek throw Exceptions if there is no object.

System.out.println("\nPriorityQueue Example");

PriorityQueue<Integer> priorityQueue = new PriorityQueue<>();

priorityQueue.add(2); // Add 0 (at END) -- Autoboxing will auto-convert int to Integer

priorityQueue.add(Integer.valueOf(98)); // Add 1 (at END) -- So don't have to do Integer.valueOf()...

priorityQueue.add(1); // Add 1 (at END)

priorityQueue.addAll(Arrays.asList(56,8,7)); // Add all of a collection.

priorityQueue.offer(0); // Add 99

priorityQueue.peek(); // Returns (doesn't remove) head element (or ele at zero index)

priorityQueue.element();

for(Integer i: priorityQueue){/* do stuff */} // Iterate Via Enhanced For Loop

Iterator priorityQueueIt = priorityQueue.iterator(); // Iterate Via ITERATOR

while (priorityQueueIt.hasNext()){priorityQueueIt.next();} // And hasNext() method.

Object[] priorityQueueObjArray = priorityQueue.toArray(); // How to convert to an Object Array:

System.out.println("priorityQueue.toString(): " + priorityQueue.toString());

System.out.println("priorityQueue.peek(): " + priorityQueue.peek());

System.out.println("priorityQueue.isEmpty(): " + priorityQueue.isEmpty());

System.out.println("priorityQueue.contains(2): " + priorityQueue.contains(2));

System.out.println("priorityQueue.size(): " + priorityQueue.size());

priorityQueue.poll(); // Remove and return the lowest value element.

priorityQueue.remove((Object) 51); // Remove object matching 2 (no exception if no match).

priorityQueue.clear();

///////////////////

// HASHSET (SET) //

///////////////////

// Uses HashMap.

// NO Order.

System.out.println("\nHashSet Example");

HashSet<Integer> hashSet = new HashSet<>();

hashSet.add(1); // Add 1

hashSet.add(1); // Doesn't do anything; already there.

hashSet.addAll(Arrays.asList(56,8,7)); // Add all of a collection.

for(Integer i: hashSet){/* do stuff */} // Iterate Via Enhanced For Loop

Iterator hashSetIt = hashSet.iterator(); // Iterate Via ITERATOR

while (hashSetIt.hasNext()){hashSetIt.next();} // And hasNext() method.

Object[] hashSetObjArray = hashSet.toArray(); // How to convert to an Object Array:

System.out.println("hashSet.toString(): " + hashSet.toString());

System.out.println("hashSet.isEmpty(): " + hashSet.isEmpty());

System.out.println("hashSet.contains(2): " + hashSet.contains(2));

System.out.println("hashSet.size(): " + hashSet.size());

hashSet.remove((Object) 51); // Remove object matching 2 (no exception if no match).

hashSet.clear();

/////////////////////////

// LINKEDHASHSET (SET) //

/////////////////////////

// Uses HashMap & LinkedList.

// IS ORDERED.

System.out.println("\nLinkedHashSet Example");

LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<>();

linkedHashSet.add(1); // Add 1 (at tail).

linkedHashSet.add(1); // Doesn't do anything; already there.

linkedHashSet.addAll(Arrays.asList(56,8,7)); // Add all of a collection.

for(Integer i: linkedHashSet){/* do stuff */} // Iterate Via Enhanced For Loop

Iterator linkedHashSetIt = linkedHashSet.iterator(); // Iterate Via ITERATOR

while (linkedHashSetIt.hasNext()){linkedHashSetIt.next();} // And hasNext() method.

Object[] linkedHashSetObjArray = linkedHashSet.toArray(); // How to convert to an Object Array:

System.out.println("linkedHashSet.toString(): " + linkedHashSet.toString());

System.out.println("linkedHashSet.isEmpty(): " + linkedHashSet.isEmpty());

System.out.println("linkedHashSet.contains(2): " + linkedHashSet.contains(2));

System.out.println("linkedHashSet.size(): " + linkedHashSet.size());

linkedHashSet.remove((Object) 51); // Remove object matching 2 (no exception if no match).

linkedHashSet.remove(999); // Removing nonexistent item is OK.

linkedHashSet.clear();

///////////////////

// TREESET (SET) //

///////////////////

// IS ORDERED

// Implemented as self balancing binary tree (Red Black Tree).

// Elements must be homogeneous and comparable.

System.out.println("\nTreeSet Example");

TreeSet<Integer> treeSet = new TreeSet<>();

treeSet.add(1); // Add 1.

treeSet.add(1); // Doesn't do anything; already there.

treeSet.addAll(Arrays.asList(5,6,8,7,9)); // Add all of a collection.

treeSet.first(); // Return first element (raises exception if none).

treeSet.last(); // Return last element (raises exception if none).

treeSet.floor(10); // Returns highest valued element <= than supplied element (10).

treeSet.ceiling(10); // Returns lowest valued element >= than than supplied ele (10).

treeSet.lower(10); // Returns highest valued element < than than supplied ele (10) or null.

treeSet.higher(10); // Returns lowest valued element > than supplied element (10) or null.

for(Integer i: treeSet){/* do stuff */} // Iterate Via Enhanced For Loop

Iterator treeSetIt = treeSet.iterator(); // Iterate Via ITERATOR

while (treeSetIt.hasNext()){treeSetIt.next();} // And hasNext() method.

Object[] treeSetObjArray = treeSet.toArray(); // How to convert to an Object Array:

System.out.println("treeSet.toString(): " + treeSet.toString());

System.out.println("treeSet.first(): " + treeSet.first());

System.out.println("treeSet.last(): " + treeSet.last());

System.out.println("treeSet.pollFirst(): " + treeSet.pollFirst());

System.out.println("treeSet.pollLast(): " + treeSet.pollLast());

System.out.println("treeSet.lower(10): " + treeSet.lower(10));

System.out.println("treeSet.higher(10): " + treeSet.higher(10));

System.out.println("treeSet.floor(10): " + treeSet.floor(10));

System.out.println("treeSet.ceiling(10): " + treeSet.ceiling(10));

System.out.println("treeSet.isEmpty(): " + treeSet.isEmpty());

System.out.println("treeSet.contains(2): " + treeSet.contains(2));

System.out.println("treeSet.size(): " + treeSet.size());

treeSet.pollFirst(); // Remove and Return first element.

treeSet.pollLast(); // Remove and Return last element.

treeSet.remove((Object) 51); // Remove object matching 2 (no exception if no match).

treeSet.remove(999);

treeSet.clear();

///////////////////////////////

// HASHMAP & HASHTABLE (MAP) //

///////////////////////////////

// HashMap ISN'T thread safe and allows ONE null key value.

// Hashtable IS thread safe, just use synchronized blocks, but DOES NOT allow any null key values.

// Another threadsafe possibility is Collections.synchronizedMap:

// Example: Map<String, Integer> syncHashMap = Collections.synchronizedMap(new HashMap<>());

System.out.println("\nHashMap/Hashtable Example");

Map<String, Integer> hash = new HashMap<>();

// Adding key-value pairs to a HashMap

hash.put("One", 1);

hash.put("Two", 2);

hash.put("Three", 3);

hash.put("Five", 5);

hash.put("Six", 6);

// Add a new key-value pair only if the key does not exist in the HashMap, or is mapped to `null`

hash.putIfAbsent("Four", 8);

// put() - How to modify a value.

hash.put("Four", 4);

// get()

System.out.println("hash.get(\"Four\"): " + hash.get("Four"));

// isEmpty()

System.out.println("hash.isEmpty(): " + hash.isEmpty());

// size()

System.out.println("hash.size(): " + hash.size());

// containsKey()

System.out.println("hash.containsKey(\"One\"): " + hash.containsKey("One"));

// containsValue()

System.out.println("hash.containsValue(1): " + hash.containsValue(1));

// remove(Key) - One arg

System.out.println("hash.remove(\"Six\"): " + hash.remove("Six"));

// remove(Key, Value) - Only removes if the Key is mapped to the Value, returns true or false.

System.out.println("hash.remove(\"Five\", 5): " + hash.remove("Five", 5));

// remove(<NonExistantKey>) returns null

System.out.println("hash.remove(\"Nine\"): " + hash.remove("Nine"));

Set<Map.Entry<String, Integer>> keysAndValueSet = hash.entrySet();

System.out.println("hash.entrySet(): " + keysAndValueSet);

// keySet()

Set<String> keySet = hash.keySet();

System.out.println("hash.keySet(): " + keySet);

// values()

Collection<Integer> valueSet = hash.values();

System.out.println("hash.values(): " + valueSet);

// Iterating using Java 8 forEach and lambda

System.out.print("Iterate with forEach and lambda: ");

hash.forEach((key, value) -> {

System.out.print(key + "=>" + value + ", ");

});

// Iterating with entrySet using iterator()

System.out.print("\nIterate with entrySet and iterator(): ");

Set<Map.Entry<String, Integer>> hashMapEntries = hash.entrySet();

Iterator<Map.Entry<String, Integer>> hashMapIterator = hashMapEntries.iterator();

while (hashMapIterator.hasNext()) {

Map.Entry<String, Integer> entry = hashMapIterator.next();

System.out.print(entry.getKey() + "=>" + entry.getValue() + ", ");

}

// Iterating with entrySet using Java 8 forEach and lambda

System.out.print("\nIterate with entrySety(), forEach, and lambda: ");

hash.entrySet().forEach(entry -> {

System.out.print(entry.getKey() + "=>" + entry.getValue() + ", ");

});

// Iterating with entrySet using simple for-each loop

System.out.print("\nIterate with entrySet() and for-each loop: ");

for(Map.Entry<String, Integer> entry: hash.entrySet()) {

System.out.print(entry.getKey() + "=>" + entry.getValue() + ", ");

}

// Iterating with keySet

System.out.print("\nIterate with keySet(): ");

hash.keySet().forEach(key -> {

System.out.print(key + "=>" + hash.get(key) + ", ");

});

System.out.println();

/////////////////////////

// EXCEPTIONS & ERRORS //

/////////////////////////

// The Exceptions and Errors are subclasses of Throwable and can be found in the java.lang package.

// ERRORS

// A represent a serious problem that should not be caught, are often related to environment, and are

// unrecoverable. All Errors are "unchecked", or are not checked at compile time.

// Examples include StackOverflowError, OutOfMemoryError, AssertionError, and VirtualMachineError.

// EXCEPTIONS

// Are a "condition that a reasonable application might want to catch", and are often more related to the

// application. RuntimeException and all of it's subclasses are "unchecked" exceptions, all other Exceptions

// are "checked" exceptions, or are checked at compile time, and must be added to a classes/methods throw clause.

// Examples include IOException, ArrayIndexOutOfBoundsException, NullPointerException, and ClassCastException.

System.out.println("\nExceptions Example");

try{

int badInt = 10/0;

}catch (ArithmeticException ex){

System.out.println("Can't divide by zero");

System.out.println(ex.getMessage());

System.out.println(ex.toString());

// Catch two exceptions in one catch block

} catch( NullPointerException | ArrayIndexOutOfBoundsException e) {

System.out.println(e.getMessage());

// Generic catch all:

}catch (Exception ex){

System.out.println(ex.getMessage());

// Finally always executes (unless thread is killed), even if a return statement is in try body.

}finally {

System.out.println("Clean up here, Close DBs, Etc...");

}

// THROW A CUSTOM EXCEPTION

try{

throw new Exception("BAD STUFF");

}catch (ArithmeticException ex){

System.out.println("Can't divide by zero");

System.out.println(ex.getMessage());

System.out.println(ex.toString());

}catch (Exception ex){

System.out.println(ex.getMessage());

}finally {

System.out.println("Clean up here, Close DBs, Etc...");

}

///////////

// FILES //

///////////

System.out.println("\nFile IO Examples");

// How to CREATE and RENAME a file:

File f1 = new File("f1.log");

File f1NewName = new File("F1BU.log");

try{

if(f1.createNewFile()){

System.out.println("File created");

f1.renameTo(f1NewName);

// NOTE: Delete DOES NOT work if you changed the name of the file:

f1.delete();

}else{

System.out.println("File not created");

}

}catch (IOException e){

e.printStackTrace();

}

// How to WRITE to a File:

File f2 = new File("f2.txt");

try{

PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter(f2)));

pw.println("This is sample text");

pw.close();

}catch (IOException e){

e.printStackTrace();

}

// How to READ from a File:

f2 = new File("f2.txt");

try{

BufferedReader br = new BufferedReader(new FileReader(f2));

String text = br.readLine();

while(text != null){

System.out.println(text);

text = br.readLine();

}

br.close();

}catch (IOException e){

e.printStackTrace();

}

// How to write BINARY DATA:

File f3 = new File("f3.dat");

FileOutputStream fos;

try{

fos = new FileOutputStream(f3);

BufferedOutputStream bos = new BufferedOutputStream(fos);

// NOTE: To write primitives you need DataOutputStream

DataOutputStream dos = new DataOutputStream(bos);

String name = "Matt";

int age = 37;

double bal = 1234.56;

dos.writeUTF(name);

dos.writeInt(age);

dos.writeDouble(bal);

dos.close();

} catch (IOException e){

e.printStackTrace();

}

// How to READ BINARY files

f3 = new File("f3.dat");

FileInputStream fis;

try{

fis = new FileInputStream(f3);

BufferedInputStream bis = new BufferedInputStream(fis);

DataInputStream dis = new DataInputStream(bis);

System.out.println(dis.readUTF());

System.out.println(dis.readInt());

System.out.println(dis.readDouble());

fis.close();

} catch (IOException e){

e.printStackTrace();

}

// How to get the Absolute and Canonical PATHS of FILES.

try {

System.out.println("Absolute Path: " + f3.getAbsolutePath());

System.out.println("Canonical Path: " + f3.getCanonicalPath());

System.out.println("Path: " + f3.getPath());

}catch(IOException e){

e.printStackTrace();

}

// How to get the PATH of the current working DIR:

Path currentRelativePath = Paths.get("");

String s = currentRelativePath.toAbsolutePath().toString();

System.out.println("Current relative path is: " + s);

// How to READ files from a DIRECTORY:

File d1 = new File(s);

System.out.print(s + ": ");

if(d1.isDirectory()){

File[] files = d1.listFiles();

for(File f : files) System.out.print(f.getName() + " ");

}

System.out.println();

// Check if a DELETE worked using java.io.File.delete()

if(f1NewName.delete()) {

System.out.println("File " + f1NewName.getName() + " deleted successfully");

} else {

System.out.println("Failed to delete the file " + f1NewName.getName() + ".");

}

// How to DELETE if a file exists using java.nio.file.files.deleteifexists(Path p):

try {

Files.deleteIfExists(Paths.get(f2.getAbsolutePath()));

Files.deleteIfExists(Paths.get(f3.getAbsolutePath()));

} catch(NoSuchFileException e) {

System.out.println("No such file/directory exists");

} catch(DirectoryNotEmptyException e) {

System.out.println("Directory is not empty.");

} catch(IOException e) {

System.out.println("Invalid permissions.");

}

/////////////

// CLASSES //

/////////////

// INTERFACE VS EXTENDS

// If the end class "IS" something (but WITHOUT additional functionality) then use EXTENDS

// If the end class "CAN" do something (but HAS additional functionality) then use INTERFACE.

// Interfaces are more flexible than abstract classes, abstracting the 'what' from the 'how'.

// Use interfaces on UNRELATED classes.

// COMPOSITION VS INHERITANCE

// Composition (HAS A relation) is accomplished by including an INSTANCE of another class as a FIELD of your class

// Inheritance (IS A relation) is accomplished by by EXTENDING another class in your class

// MISC. CLASS STUFF

// super. - used to access/call the parent class members.

// super() - Only way to call parent constructor, must be first statement in constructor.

// this. - used to call the current class members (fields and methods), can't use in static context.

// this() - Only way to call a constructor (used for CONSTRUCTOR CHAINING). Must be first statement.

// Constructor can't have call to both super() and this().

// If a class is final or has a private constructor it can't be subclassed.

// 4 TYPES OF NESTED CLASS

// static nested class

// non-static nested class (inner class)

// local class (inner class in a scope block/method) -- not used often, in theory, helps with encapsulation.

// anonymous nested class (no class name) -- used only once, used a lot with attaching event handlers to

// buttons (for example, in android apps).

// How to instantiate classes.

Rectangle rectangle = new Rectangle(0,0, true, 10, 10);

Circle circle = new Circle(0, 0 , true, 1);

// How to determine if something is an instance of a specific class:

if(rectangle instanceof Rectangle){

System.out.println("(rectangle instanceof Rectangle) :" + (rectangle instanceof Rectangle));

}

SerializationReview.examples();

LambdaReview.examples();

StreamReview.examples();

ConcurrentReview.examples();

GCReview.examples();

// How to exit; this terminates the currently running Java Virtual Machine. The argument serves as a status

// code; by convention, a nonzero status code indicates abnormal termination.

System.exit(0);

} // END OF MAIN

}

class Shape{

// STATIC MEMBER VARIABLE

// SHARED by all instances of the class. i.e., scanners or loggers.

private static int numberOfShapes = 0;

// Instance Variables aka Fields aka Member Variables.

private double xLocation;

private double yLocation;

private boolean visible;

// Constructor

public Shape(double xLocation, double yLocation, boolean visible){

this.xLocation = xLocation;

this.yLocation = yLocation;

this.visible = visible;

numberOfShapes++;

}

// INSTANCE METHOD

// This method is created when the class is instantiated with the "new" keyword.

public void instanceMethod(){

}

// STATIC METHODS

// CAN'T access instance methods and instance variables directly (NO this.<whatev>..).

// Are not made when class is instantiated.

public static void staticMethod(){

}

// MULTIPLE METHOD ARGS

public static void multipleArgsMethod(int ... vals){

for(int x : vals){

// Do something...

}

// See child class for Method Overriding.

public void methodOverridingExample(){

}

// Deprecated!

// A method called before object is garbage collected (Not a destructor, but often compared to a destructor).

// Only use for logging.

public void finalize(){

}

// EXTENDS SHAPE

class Rectangle extends Shape{

private double width;

private double heigth;

// CONSTRUCTOR CHAINING

public Rectangle(double x, double y, boolean visible){

this(x, y, visible, 0, 0);

}

public Rectangle(double xLocation, double yLocation, boolean visible, double width, double heigth){

super(xLocation, yLocation, visible);

this.width = width;

this.heigth = heigth;

}

// METHOD OVERLOADING

// Must have same name, must have different parameters, CAN have different return types, CAN have different

// modifiers, CAN throw different checked or unchecked exceptions.

public void methodOverloadExample(){

}

private boolean methodOverloadExample(int x){

return true;

}

// METHOD OVERRIDING

// JVM will determine what method will be called at RUNTIME. SHOULD (but don't have to) annotate with @Override.

// CAN'T override static methods (only instance methods).

// Only inherited methods can be overridden, constructors and private and final methods CAN'T be overridden.

// Use: super.methodName() to call the superclass version of an overridden method.

// MUST have same name and args, return type CAN be a subclass of the return type in the parent class,

// it CAN'T have a lower access modifier (if parent is protected then private child ISN'T allowed, can be public)

@Override

public void methodOverridingExample(){

}

class Circle extends Shape{

private double radius;

public Circle(double x, double y, boolean visible, double radius){

super(x, y, visible);

this.radius = radius;

}

//////////////////////

// ABSTRACT CLASSES //

//////////////////////

abstract class AbstractClassEmpty {

}

// CAN EXTENDS or IMPLEMENT in an abstract class.

abstract class AbstractClass extends AbstractClassEmpty implements InterfaceClassEmpty {

// Can have member variables that are inherited (can't in interface unless static).

private String name;

// Can have a constructor (interfaces can't)

public AbstractClass(String name){

this.name = name;

}

// Can have non-abstract methods (that have bodies) in an abstract class

public String getName() {

return name;

}

// Remember that any class that implements (extends) this class must implement ALL of the things defined in this,

// Where if they extended a base class, they can choose what they want to implement.

// Only methods (and class) are allowed to be abstract.

// Methods that are abstract don't have bodies (but you can have non-abstract methods that must have bodies in an abstract class).

public abstract void doSomething();

public abstract void doSomethingElse(int someInt);

}

class Teeest extends AbstractClass{

public Teeest(){

super("blah");

}

public void doSomething(){

return;

}

public void doSomethingElse(int someInt){

return;

}

////////////////

// INTERFACES //

////////////////

interface InterfaceClassEmpty {

}

interface IAnotherEmptyClass{

}

// An interface can ONLY extend an interface (can't implement an interface, can't extend an abstract class).

interface InterfaceClass extends InterfaceClassEmpty, IAnotherEmptyClass{

// Can ONLY have public static variables.

public static String staticString = "Only static variables are allowed.";

public static final int STATIC_INT = 838;

// Pre-Java9, Can ONLY have public methods (no private or protected).

public void interfaceMethod();

public boolean interfaceMethodWithArg(int i);

// SINCE JAVA 9, Interfaces can have private methods.

//private void privateMethod();

// SINCE JAVA 8, Interfaces can contain default methods (with implementation).

default void defaultMethod(int defaultArg){

System.out.println("Can actually implement something (have a body of a method in an Interface).");

}

//////////////

// GENERICS //

//////////////

// Generics enable types (classes and interfaces) to be parameters when defining classes, interfaces and methods.

// Added to Java5

// Benefits include code reuse, type safety, elimination of casts, and ability for generic algorithms.

interface InterfaceGenericClass<T>{

}

abstract class AbstractGenericClass<T>{

}

// Can have multiple types:

class ClassWithGenerics<T extends Comparable, U>{

T val;

public void setVal(T val){

this.val = val;

}

// Static generic method:

// Static keyword must have matching Generic type if generic type used anywhere in method.

// Static generic methods can be used in non-generic classes.

public static<T extends Object> void staticMethod(T[] arr){

System.out.println("I'm staticMethod in ClassWithGenerics...");

}

public T getVal(){

return val;

}

public void usingRawAndGenerics() {

// List using raw types:.

ArrayList rawTypesList = new ArrayList();

rawTypesList.add(1);

rawTypesList.add("hi");

rawTypesList.add(1.2);

// List using generics:

ArrayList<Integer> intList = new ArrayList<>();

intList.add(144);

}

// Must typecast when referencing; prone to run time errors.

public static void printArrayList(ArrayList<?> aL){

for(Object x : aL) System.out.println(x);

}

////////////////

// COMPARATOR //

////////////////

// Comparator interface is used to order the objects of user-defined classes.

// A comparator object is capable of comparing two objects of two different classes.

// Usage Example:

// String[] stringArray = new String[]{"they", "fun", "race", "fights", "care", "listens", "silent", "acre"};

// Arrays.sort(stringArray, new AnagramComparator());

// This example would sort each string in a string array so that anagrams would be ordered next to each other.

class AnagramComparator implements Comparator<String>{

public String sortChars(String s){

char[] content = s.toCharArray();

Arrays.sort(content);

return new String(content);

}

// Must implement compare when implementing Comparator.

public int compare(String s1, String s2){

return sortChars(s1).compareTo(sortChars(s2));

}

// How to implement a Comparator as an Anonymous Class (Say if you wanted to do this in main()):

public void howToImplementComparatorViaAnonymousClass(){

String[] stringArray = new String[]{"they", "fun", "race", "fights", "care", "listens", "silent", "acre"};

Arrays.sort(stringArray, new Comparator<String>() {

@Override

public int compare(String s1, String s2) {

char[] content1 = s1.toCharArray();

Arrays.sort(content1);

char[] content2 = s2.toCharArray();

Arrays.sort(content2);

return (new String(content1)).compareTo(new String(content2));

}

});

}

///////////////////////////////////////////////////

// SERIALIZATION (SERIALIZABLE & EXTERNALIZABLE) //

///////////////////////////////////////////////////

// Serialization, in Java, is the process which is used to serialize object in java by storing object’s state into a

// file and recreating object's state from that file (the reverse process is called deserialization). The file (byte

// stream) created is platform independent, therefore, an object serialized on one platform can be deserialized on a

// different platform. This is useful for network communication and to save objects states.

// NOTE: Any object being serialized (from an serialized object) MUST ALSO be serialized or a

// java.io.NotSerializableException will be thrown.

// The Java Serialization API provides the Serializable interface and the Externalizable interface as object

// serialization mechanisms.

// SERIALIZABLE INTERFACE

// Serializable is a MARKER INTERFACE, or, an interface that has no methods or constants inside it, and is intended to

// provide information to the compiler and JVM. Therefore, to make a class Serializable, add "implements

// java.io.Serializable", then the JVM will provide default serialization. The default serialization is serialization

// of all non-static and non-transient data members. Variables defined with transient keyword are initialized with the

// default value (NOT current value) during deserialization. Variables defined with static keyword are loaded with the

// current value of the variable during deserialization.

// EXTERNALIZABLE INTERFACE

// The Externalizable interface, which extends Serializable, allows for flexibility and control of object serialization

// via writeExternal() and readExternal() methods. When overriding these two methods, the user can specify/customize

// the items that are read and written, thus, allowing for better control and backwards compatibility. Contrary to the

// Serializable interface, the Externalizable interface CAN write/read transient and static variables.

// NOTE: The same items and order must be used during writing (writeExternal()) and reading (readExternal()).

// NOTE: There must be a public default no-arg constructor to use readObject() on an object that implemented

// Externalizable, or a java.io.InvalidClassException will be thrown.

// SERIALVERSIONUID

// The Serialization runtime associates a version number with each Serializable class called, this number is the

// serialVersionUID. This is used during Deserialization to verify that the sender and receiver of a serialized object

// have loaded compatible classes (w.r.t. serialization). If the serialVersionUID differ during Deserialization, then a

// InvalidClassException will be thrown. If no serialVersionUID is defined, Java will automatically create one based on

// the class'es attributes (note that small changes in the class can cause a different ID). It is considered good

// practice to define your own serialVersionUID; to do this, define "static final long serialVersionUID" and assign it

// to a type of long value.

// SERIALVER

// serialver is a tool that comes with JDK. It is used to get serialVersionUID number for Java classes. The tool is used

// via the following command:

// serialver [-classpath classpath] [-show] [classname…]

class SerializationReview{

public static void examples(){

SerializableClass serializableClass = new SerializableClass();

SerializableClass readSerializableClass = null;

serializableClass.transientInt = 8008;

serializableClass.staticInt = 6;

serializableClass.string = "Hello World!";

serializableClass.i = 42;

ExternalizableClass externalizableClass = new ExternalizableClass();

ExternalizableClass readExternalizableClass = null;

externalizableClass.transientInt = 80085;

externalizableClass.staticInt = 69;

externalizableClass.string = "Hello World!!!";

externalizableClass.i = 420;

System.out.println(serializableClass.toString());

System.out.println(externalizableClass.toString());

try {

// Serialize serializableClass:

ObjectOutputStream so = new ObjectOutputStream(new FileOutputStream("serializableClass.txt"));

so.writeObject(serializableClass);

so.flush();

so.close();

// Serialize externalizableClass:

so = new ObjectOutputStream(new FileOutputStream("externalizableClass.txt"));

so.writeObject(externalizableClass);

so.flush();

so.close();

serializableClass.transientInt = 800;

serializableClass.staticInt = -6;

serializableClass.string = "Hello!";

serializableClass.i = 4;

externalizableClass.transientInt = 800850;

externalizableClass.staticInt = 690;

externalizableClass.string = "Hello World!!!!!!!!!!!";

externalizableClass.i = 4200;

// Deserialize serializableClass:

ObjectInputStream si = new ObjectInputStream(new FileInputStream("serializableClass.txt"));

readSerializableClass = (SerializableClass)si.readObject();

si.close();

// Deserialize externalizableClass:

si = new ObjectInputStream(new FileInputStream("externalizableClass.txt"));

readExternalizableClass = (ExternalizableClass)si.readObject();

si.close();

// Delete files:

File f = new File("serializableClass.txt");

f.delete();

f = new File("externalizableClass.txt");

f.delete();

} catch (Exception e) {

System.out.println(e);