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+---
+
+language: java
+
+author: Jake Prather
+
+author_url: http://github.com/JakeHP
+
+filename: LearnJava.java
+
+---
+
+Java is a general-purpose, concurrent, class-based, object-oriented computer programming language.
+[Read more here.](http://docs.oracle.com/javase/tutorial/java/index.html)
+
+```java
+// Single-line comments start with //
+/*
+Multi-line comments look like this.
+*/
+
+// Import ArrayList class inside of the java.util package
+import java.util.ArrayList;
+// Import all classes inside of java.security package
+import java.security.*;
+
+// Each .java file contains one public class, with the same name as the file.
+public class LearnJava {
+
+ // A program must have a main method as an entry point
+ public static void main (String[] args) {
+
+ // Use System.out.println to print lines
+ System.out.println("Hello World!");
+ System.out.println(
+ "Integer: " + 10 +
+ " Double: " + 3.14 +
+ " Boolean: " + true);
+
+ // To print without a newline, use System.out.print
+ System.out.print("Hello ");
+ System.out.print("World");
+
+
+ ///////////////////////////////////////
+ // Types & Variables
+ ///////////////////////////////////////
+
+ // Declare a variable using <type> <name> [
+ // Byte - 8-bit signed two's complement integer
+ // (-128 <= byte <= 127)
+ byte fooByte = 100;
+
+ // Short - 16-bit signed two's complement integer
+ // (-32,768 <= short <= 32,767)
+ short fooShort = 10000;
+
+ // Integer - 32-bit signed two's complement integer
+ // (-2,147,483,648 <= int <= 2,147,483,647)
+ int fooInt = 1;
+
+ // Long - 64-bit signed two's complement integer
+ // (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807)
+ long fooLong = 100000L;
+
+ // (Java has no unsigned types)
+
+ // Float - Single-precision 32-bit IEEE 754 Floating Point
+ float fooFloat = 234.5f;
+
+ // Double - Double-precision 64-bit IEEE 754 Floating Point
+ double fooDouble = 123.4;
+
+ // Boolean - true & false
+ boolean fooBoolean = true;
+ boolean barBoolean = false;
+
+ // Char - A single 16-bit Unicode character
+ char fooChar = 'A';
+
+ // Use final to make a variable immutable
+ final int HOURS_I_WORK_PER_WEEK = 9001;
+
+ // Strings
+ String fooString = "My String Is Here!";
+
+ // \n is an escaped character that starts a new line
+ String barString = "Printing on a new line?\nNo Problem!";
+ System.out.println(fooString);
+ System.out.println(barString);
+
+ // Arrays
+ //The array size must be decided upon declaration
+ //The format for declaring an array is follows:
+ //<datatype> [] <var name> = new <datatype>[<array size>];
+ int [] intArray = new int[10];
+ String [] stringArray = new String[1];
+ boolean [] booleanArray = new boolean[100];
+
+ // Another way to declare & initialize an array
+ int [] y = {9000, 1000, 1337};
+
+ // Indexing an array - Accessing an element
+ System.out.println("intArray @ 0: " + intArray[0]);
+
+ // Arrays are zero-indexed and mutable.
+ intArray[1] = 1;
+ System.out.println("intArray @ 1: " + intArray[1]); // => 1
+
+ // Others to check out
+ // ArrayLists - Like arrays except more functionality is offered,
+ // and the size is mutable
+ // LinkedLists
+ // Maps
+ // HashMaps
+
+ ///////////////////////////////////////
+ // Operators
+ ///////////////////////////////////////
+ System.out.println("\n->Operators");
+
+ int i1 = 1, i2 = 2; // Shorthand for multiple declarations
+
+ // Arithmetic is straightforward
+ System.out.println("1+2 = " + (i1 + i2)); // => 3
+ System.out.println("2-1 = " + (i2 - i1)); // => 1
+ System.out.println("2*1 = " + (i2 * i1)); // => 2
+ System.out.println("1/2 = " + (i1 / i2)); // => 0 (0.5 truncated down)
+
+ // Modulo
+ System.out.println("11%3 = "+(11 % 3)); // => 2
+
+ // Comparison operators
+ System.out.println("3 == 2? " + (3 == 2)); // => 0 (false)
+ System.out.println("3 != 2? " + (3 != 2)); // => 1 (true)
+ System.out.println("3 > 2? " + (3 > 2)); // => 1
+ System.out.println("3 < 2? " + (3 < 2)); // => 0
+ System.out.println("2 <= 2? " + (2 <= 2)); // => 1
+ System.out.println("2 >= 2? " + (2 >= 2)); // => 1
+
+ // Bitwise operators!
+ /*
+ ~ Unary bitwise complement
+ << Signed left shift
+ >> Signed right shift
+ >>> Unsigned right shift
+ & Bitwise AND
+ ^ Bitwise exclusive OR
+ | Bitwise inclusive OR
+ */
+
+ // Incrementations
+ int i=0;
+ System.out.println("\n->Inc/Dec-rementation");
+ System.out.println(i++); //i = 1. Post-Incrementation
+ System.out.println(++i); //i = 2. Pre-Incrementation
+ System.out.println(i--); //i = 1. Post-Decrementation
+ System.out.println(--i); //i = 0. Pre-Decrementation
+
+ ///////////////////////////////////////
+ // Control Structures
+ ///////////////////////////////////////
+ System.out.println("\n->Control Structures");
+
+ // If statements are c-like
+ if (false){
+ System.out.println("I never run");
+ }else if (false) {
+ System.out.println("I am also never run");
+ } else {
+ System.out.println("I print");
+ }
+
+ // While loop
+ int fooWhile = 0;
+ while(fooWhile < 100)
+ {
+ //System.out.println(fooWhile);
+ //Increment the counter
+ //Iterated 99 times, fooWhile 0->99
+ fooWhile++;
+ }
+ System.out.println("fooWhile Value: " + fooWhile);
+
+ // Do While Loop
+ int fooDoWhile = 0;
+ do
+ {
+ //System.out.println(fooDoWhile);
+ //Increment the counter
+ //Iterated 99 times, fooDoWhile 0->99
+ fooDoWhile++;
+ }while(fooDoWhile < 100);
+ System.out.println("fooDoWhile Value: " + fooDoWhile);
+
+ // For Loop
+ int fooFor;
+ //for loop structure => for(<start_statement>; <conditional>; <step>)
+ for(fooFor=0; fooFor<10; fooFor++){
+ //System.out.println(fooFor);
+ //Iterated 10 times, fooFor 0->9
+ }
+ System.out.println("fooFor Value: " + fooFor);
+
+ // Switch Case
+ int month = 3;
+ String monthString;
+ switch (month){
+ case 1: monthString = "January";
+ break;
+ case 2: monthString = "February";
+ break;
+ case 3: monthString = "March";
+ break;
+ default: monthString = "Some other month";
+ break;
+ }
+ System.out.println("Switch Case Result: " + monthString);
+
+
+ ///////////////////////////////////////
+ // Converting Data Types And Typcasting
+ ///////////////////////////////////////
+
+ // Converting data
+
+ // Convert String To Integer
+ Integer.parseInt("123");//returns an integer version of "123"
+
+ // Convert Integer To String
+ Integer.toString(123);//returns a string version of 123
+
+ // For other conversions check out the following classes:
+ // Double
+ // Long
+ // String
+
+ // Typecasting
+ // You can also cast java objects, there's a lot of details and
+ // deals with some more intermediate concepts.
+ // Feel free to check it out here:
+ // http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
+
+
+ ///////////////////////////////////////
+ // Classes And Functions
+ ///////////////////////////////////////
+
+ System.out.println("\n->Classes & Functions");
+
+ // (definition of the Bicycle class follows)
+
+ // Use new to instantiate a class
+ Bicycle trek = new Bicycle();
+
+ // Call object methods
+ trek.speedUp(3);
+ trek.setCadence(100);
+
+ // toString is a convention
+ System.out.println("trek info: " + trek.toString());
+
+ } // End main method
+} // End LearnJava class
+
+
+// You can include other, non-public classes in a .java file
+
+
+// Class Declaration Syntax:
+// <public/private/protected> class <class name>{
+// //data fields, constructors, functions all inside
+// }
+
+class Bicycle {
+
+ // Bicycle's Fields/Variables
+ public int cadence; // Public: Can be accessed from anywhere
+ private int speed; // Private: Only accessable from within the class
+ protected int gear; // Protected: Accessible from the class and subclasses
+
+ // Constructors are a way of creating classes
+ // This is a default constructor
+ public Bicycle() {
+ gear = 1;
+ cadence = 50;
+ speed = 5;
+ }
+
+ // This is a specified constructor (it contains arguments)
+ public Bicycle(int startCadence, int startSpeed, int startGear) {
+ gear = startGear;
+ cadence = startCadence;
+ speed = startSpeed;
+ }
+
+ // Function Syntax:
+ // <public/private/protected> <return type> <function name>(<args>)
+
+ // Java classes often implement getters and setters for their fields
+
+ // Method declaration syntax:
+ // <scope> <return type> <method name>(<args>)
+ public int getCadence() {
+ return cadence;
+ }
+
+ // void methods require no return statement
+ public void setCadence(int newValue) {
+ cadence = newValue;
+ }
+
+ public void setGear(int newValue) {
+ gear = newValue;
+ }
+
+ public void speedUp(int increment) {
+ speed += increment;
+ }
+
+ public void slowDown(int decrement) {
+ speed -= decrement;
+ }
+
+ public String toString() {
+ return "gear: "+Integer.toString(gear)+
+ " cadence: "+Integer.toString(cadence)+
+ " speed: "+Integer.toString(speed);
+ }
+} // end class Bicycle
+
+// PennyFarthing is a subclass of Bicycle
+class PennyFarthing extends Bicycle {
+ // (Penny Farthings are those bicycles with the big front wheel.
+ // They have no gears.)
+
+ public PennyFarthing(int startCadence, int startSpeed){
+ // Call the parent constructor with super
+ super(startCadence, startSpeed, 0);
+ }
+
+ // You should mark a method you're overriding with an @annotation
+ @Override
+ public void setGear(int gear) {
+ gear = 0;
+ }
+
+}
+
+```
+
+## Further Reading
+
+Other Topics To Research:
+
+* [Inheritance](http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html)
+
+* [Polymorphism](http://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html)
+
+* [Abstraction](http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html)
+
+* [Exceptions](http://docs.oracle.com/javase/tutorial/essential/exceptions/index.html)
+
+* [Interfaces](http://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html)
+
+* [Generics](http://docs.oracle.com/javase/tutorial/java/generics/index.html)
+
+* [Java Code Conventions](http://www.oracle.com/technetwork/java/codeconv-138413.html)
+
+* The links provided are just to get an understanding of the topic, feel free to google and find specific examples