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Merge pull request #1371 from zfergus2/master
[java/en] Added additional definitions and edited comments
This commit is contained in:
Levi Bostian
commit
89c63424f3
@ -5,6 +5,7 @@ contributors:
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- ["Jakukyo Friel", "http://weakish.github.io"]
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- ["Madison Dickson", "http://github.com/mix3d"]
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- ["Simon Morgan", "http://sjm.io/"]
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- ["Zachary Ferguson", "http://github.com/zfergus2"]
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filename: LearnJava.java
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---
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@ -31,7 +32,7 @@ import java.security.*;
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// the file.
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public class LearnJava {
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// A program must have a main method as an entry point.
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// In order to run a java program, it must have a main method as an entry point.
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public static void main (String[] args) {
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// Use System.out.println() to print lines.
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@ -45,6 +46,8 @@ public class LearnJava {
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System.out.print("Hello ");
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System.out.print("World");
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// Use System.out.printf() for easy formatted printing.
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System.out.printf("pi = %.5f", Math.PI); // => pi = 3.14159
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///////////////////////////////////////
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// Variables
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@ -93,7 +96,7 @@ public class LearnJava {
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// Float - Single-precision 32-bit IEEE 754 Floating Point
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float fooFloat = 234.5f;
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// f is used to denote that this variable value is of type float;
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// f or F is used to denote that this variable value is of type float;
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// otherwise it is treated as double.
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// Double - Double-precision 64-bit IEEE 754 Floating Point
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@ -106,9 +109,12 @@ public class LearnJava {
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// Char - A single 16-bit Unicode character
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char fooChar = 'A';
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// final variables can't be reassigned to another object.
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// final variables can't be reassigned to another object,
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final int HOURS_I_WORK_PER_WEEK = 9001;
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// but they can be initialized later.
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final double E;
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E = 2.71828;
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// Strings
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String fooString = "My String Is Here!";
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@ -166,6 +172,7 @@ public class LearnJava {
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System.out.println("2-1 = " + (i2 - i1)); // => 1
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System.out.println("2*1 = " + (i2 * i1)); // => 2
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System.out.println("1/2 = " + (i1 / i2)); // => 0 (0.5 truncated down)
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System.out.println("1/2 = " + (i1 / (i2*1.0))); // => 0.5
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// Modulo
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System.out.println("11%3 = "+(11 % 3)); // => 2
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@ -178,12 +185,17 @@ public class LearnJava {
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System.out.println("2 <= 2? " + (2 <= 2)); // => true
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System.out.println("2 >= 2? " + (2 >= 2)); // => true
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// Boolean operators
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System.out.println("3 > 2 && 2 > 3? " + ((3 > 2) && (2 > 3))); // => false
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System.out.println("3 > 2 || 2 > 3? " + ((3 > 2) || (2 > 3))); // => true
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System.out.println("!(3 == 2)? " + (!(3 == 2))); // => true
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// Bitwise operators!
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/*
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~ Unary bitwise complement
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<< Signed left shift
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>> Signed right shift
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>>> Unsigned right shift
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>> Signed/Arithmetic right shift
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>>> Unsigned/Logical right shift
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& Bitwise AND
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^ Bitwise exclusive OR
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| Bitwise inclusive OR
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@ -236,9 +248,8 @@ public class LearnJava {
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System.out.println("fooDoWhile Value: " + fooDoWhile);
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// For Loop
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int fooFor;
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// for loop structure => for(<start_statement>; <conditional>; <step>)
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for (fooFor = 0; fooFor < 10; fooFor++) {
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for (int fooFor = 0; fooFor < 10; fooFor++) {
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System.out.println(fooFor);
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// Iterated 10 times, fooFor 0->9
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}
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@ -332,9 +343,9 @@ public class LearnJava {
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private static final Set<String> COUNTRIES = new HashSet<String>();
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static {
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validCodes.add("DENMARK");
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validCodes.add("SWEDEN");
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validCodes.add("FINLAND");
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validCodes.add("DENMARK");
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validCodes.add("SWEDEN");
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validCodes.add("FINLAND");
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}
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// But there's a nifty way to achive the same thing in an
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@ -357,7 +368,8 @@ public class LearnJava {
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} // End LearnJava class
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// You can include other, non-public outer-level classes in a .java file
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// You can include other, non-public outer-level classes in a .java file,
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// but it is good practice. Instead split classes into separate files.
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// Class Declaration Syntax:
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@ -377,6 +389,8 @@ class Bicycle {
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// Constructors are a way of creating classes
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// This is a constructor
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public Bicycle() {
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// You can also call another constructor:
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// this(1, 50, 5, "Bontrager");
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gear = 1;
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cadence = 50;
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speed = 5;
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@ -392,13 +406,13 @@ class Bicycle {
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this.name = name;
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}
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// Function Syntax:
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// Method Syntax:
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// <public/private/protected> <return type> <function name>(<args>)
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// Java classes often implement getters and setters for their fields
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// Method declaration syntax:
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// <scope> <return type> <method name>(<args>)
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// <access modifier> <return type> <method name>(<args>)
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public int getCadence() {
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return cadence;
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}
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@ -429,7 +443,7 @@ class Bicycle {
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}
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//Method to display the attribute values of this Object.
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@Override
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@Override // Inherited from the Object class.
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public String toString() {
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return "gear: " + gear + " cadence: " + cadence + " speed: " + speed +
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" name: " + name;
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@ -464,26 +478,26 @@ class PennyFarthing extends Bicycle {
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// Example - Food:
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public interface Edible {
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public void eat(); // Any class that implements this interface, must
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public void eat(); // Any class that implements this interface, must
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// implement this method.
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}
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public interface Digestible {
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public void digest();
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public void digest();
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}
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// We can now create a class that implements both of these interfaces.
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public class Fruit implements Edible, Digestible {
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@Override
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public void eat() {
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// ...
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}
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public void eat() {
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// ...
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}
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@Override
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public void digest() {
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// ...
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}
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public void digest() {
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// ...
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}
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}
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// In Java, you can extend only one class, but you can implement many
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@ -491,81 +505,120 @@ public class Fruit implements Edible, Digestible {
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public class ExampleClass extends ExampleClassParent implements InterfaceOne,
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InterfaceTwo {
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@Override
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public void InterfaceOneMethod() {
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}
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public void InterfaceOneMethod() {
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}
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@Override
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public void InterfaceTwoMethod() {
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}
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public void InterfaceTwoMethod() {
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}
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}
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// Abstract Classes
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// Abstract Class declaration syntax
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// <access-level> abstract <abstract-class-name> extends <super-abstract-classes> {
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// // Constants and variables
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// // Method declarations
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// }
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// Methods can't have bodies in an interface, unless the method is
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// static. Also variables are NOT final by default, unlike an interface.
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// Also abstract classes CAN have the "main" method.
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// Abstract classes solve these problems.
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// Marking a class as abstract means that it contains abstract methods that must
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// be defined in a child class. Similar to interfaces, abstract classes cannot
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// be instantiated, but instead must be extended and the abstract methods
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// defined. Different from interfaces, abstract classes can contain a mixture of
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// concrete and abstract methods. Methods in an interface cannot have a body,
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// unless the method is static, and variables are final by default, unlike an
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// abstract class. Also abstract classes CAN have the "main" method.
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public abstract class Animal
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{
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public abstract void makeSound();
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public abstract void makeSound();
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// Method can have a body
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public void eat()
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{
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System.out.println("I am an animal and I am Eating.");
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// Note: We can access private variable here.
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age = 30;
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}
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// Method can have a body
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public void eat()
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{
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System.out.println("I am an animal and I am Eating.");
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// Note: We can access private variable here.
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age = 30;
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}
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// No need to initialize, however in an interface
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// a variable is implicitly final and hence has
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// to be initialized.
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private int age;
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// No need to initialize, however in an interface
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// a variable is implicitly final and hence has
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// to be initialized.
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protected int age;
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public void printAge()
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{
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System.out.println(age);
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}
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public void printAge()
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{
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System.out.println(age);
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}
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// Abstract classes can have main function.
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public static void main(String[] args)
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{
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System.out.println("I am abstract");
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}
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// Abstract classes can have main function.
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public static void main(String[] args)
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{
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System.out.println("I am abstract");
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}
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}
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class Dog extends Animal
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{
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// Note still have to override the abstract methods in the
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// abstract class.
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@Override
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public void makeSound()
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{
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System.out.println("Bark");
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// age = 30; ==> ERROR! age is private to Animal
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}
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// Note still have to override the abstract methods in the
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// abstract class.
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@Override
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public void makeSound()
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{
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System.out.println("Bark");
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// age = 30; ==> ERROR! age is private to Animal
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}
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// NOTE: You will get an error if you used the
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// @Override annotation here, since java doesn't allow
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// overriding of static methods.
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// What is happening here is called METHOD HIDING.
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// Check out this awesome SO post: http://stackoverflow.com/questions/16313649/
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public static void main(String[] args)
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{
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Dog pluto = new Dog();
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pluto.makeSound();
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pluto.eat();
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pluto.printAge();
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}
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// NOTE: You will get an error if you used the
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// @Override annotation here, since java doesn't allow
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// overriding of static methods.
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// What is happening here is called METHOD HIDING.
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// Check out this awesome SO post: http://stackoverflow.com/questions/16313649/
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public static void main(String[] args)
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{
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Dog pluto = new Dog();
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pluto.makeSound();
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pluto.eat();
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pluto.printAge();
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}
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}
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// Final Classes
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// Final Class declaration syntax
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// <access-level> final <final-class-name> {
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// // Constants and variables
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// // Method declarations
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// }
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// Final classes are classes that cannot be inherited from and are therefore a
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// final child. In a way, final classes are the opposite of abstract classes
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// because abstract classes must be extended, but final classes cannot be
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// extended.
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public final class SaberToothedCat extends Animal
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{
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// Note still have to override the abstract methods in the
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// abstract class.
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@Override
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public void makeSound()
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{
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System.out.println("Roar");
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}
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}
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// Final Methods
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public abstract class Mammal()
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{
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// Final Method Syntax:
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// <access modifier> final <return type> <function name>(<args>)
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// Final methods, like, final classes cannot be overridden by a child class,
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// and are therefore the final implementation of the method.
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public final boolean isWarmBlooded()
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{
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return true;
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}
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}
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```
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## Further Reading
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