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removed whitespaces, fixed content extending beyond 80 chars
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@ -8,6 +8,7 @@ contributors:
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- ["Zachary Ferguson", "http://github.com/zfergus2"]
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- ["Zachary Ferguson", "http://github.com/zfergus2"]
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- ["Cameron Schermerhorn", "http://github.com/cschermerhorn"]
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- ["Cameron Schermerhorn", "http://github.com/cschermerhorn"]
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- ["Rachel Stiyer", "https://github.com/rstiyer"]
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- ["Rachel Stiyer", "https://github.com/rstiyer"]
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- ["Divay Prakash", "http://github.com/divayprakash"]
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filename: LearnJava.java
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filename: LearnJava.java
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---
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---
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@ -17,9 +18,11 @@ programming language.
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```java
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```java
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// Single-line comments start with //
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// Single-line comments start with //
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/*
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/*
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Multi-line comments look like this.
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Multi-line comments look like this.
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*/
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*/
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/**
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/**
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JavaDoc comments look like this. Used to describe the Class or various
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JavaDoc comments look like this. Used to describe the Class or various
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attributes of a Class.
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attributes of a Class.
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@ -30,11 +33,12 @@ import java.util.ArrayList;
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// Import all classes inside of java.security package
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// Import all classes inside of java.security package
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import java.security.*;
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import java.security.*;
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// Each .java file contains one outer-level public class, with the same name as
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// Each .java file contains one outer-level public class, with the same name
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// the file.
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// as the file.
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public class LearnJava {
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public class LearnJava {
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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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// In order to run a java program, it must have a main method as an entry
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// point.
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public static void main (String[] args) {
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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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// Use System.out.println() to print lines.
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@ -60,7 +64,8 @@ public class LearnJava {
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*/
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*/
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// Declare a variable using <type> <name>
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// Declare a variable using <type> <name>
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int fooInt;
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int fooInt;
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// Declare multiple variables of the same type <type> <name1>, <name2>, <name3>
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// Declare multiple variables of the same
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// type <type> <name1>, <name2>, <name3>
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int fooInt1, fooInt2, fooInt3;
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int fooInt1, fooInt2, fooInt3;
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/*
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/*
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@ -69,7 +74,8 @@ public class LearnJava {
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// Initialize a variable using <type> <name> = <val>
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// Initialize a variable using <type> <name> = <val>
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int fooInt = 1;
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int fooInt = 1;
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// Initialize multiple variables of same type with same value <type> <name1>, <name2>, <name3> = <val>
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// Initialize multiple variables of same type with same
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// value <type> <name1>, <name2>, <name3> = <val>
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int fooInt1, fooInt2, fooInt3;
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int fooInt1, fooInt2, fooInt3;
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fooInt1 = fooInt2 = fooInt3 = 1;
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fooInt1 = fooInt2 = fooInt3 = 1;
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@ -119,18 +125,15 @@ public class LearnJava {
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final double E;
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final double E;
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E = 2.71828;
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E = 2.71828;
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// BigInteger - Immutable arbitrary-precision integers
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// BigInteger - Immutable arbitrary-precision integers
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//
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//
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// BigInteger is a data type that allows programmers to manipulate
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// BigInteger is a data type that allows programmers to manipulate
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// integers longer than 64-bits. Integers are stored as an array of
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// integers longer than 64-bits. Integers are stored as an array of
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// of bytes and are manipulated using functions built into BigInteger
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// of bytes and are manipulated using functions built into BigInteger
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//
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//
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// BigInteger can be initialized using an array of bytes or a string.
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// BigInteger can be initialized using an array of bytes or a string.
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BigInteger fooBigInteger = new BigInteger(fooByteArray);
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BigInteger fooBigInteger = new BigInteger(fooByteArray);
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// BigDecimal - Immutable, arbitrary-precision signed decimal number
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// BigDecimal - Immutable, arbitrary-precision signed decimal number
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//
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//
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// A BigDecimal takes two parts: an arbitrary precision integer
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// A BigDecimal takes two parts: an arbitrary precision integer
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@ -142,16 +145,13 @@ public class LearnJava {
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//
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//
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// BigDecimal can be initialized with an int, long, double or String
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// BigDecimal can be initialized with an int, long, double or String
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// or by initializing the unscaled value (BigInteger) and scale (int).
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// or by initializing the unscaled value (BigInteger) and scale (int).
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BigDecimal fooBigDecimal = new BigDecimal(fooBigInteger, fooInt);
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BigDecimal fooBigDecimal = new BigDecimal(fooBigInteger, fooInt);
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// Be wary of the constructor that takes a float or double as
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// Be wary of the constructor that takes a float or double as
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// the inaccuracy of the float/double will be copied in BigDecimal.
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// the inaccuracy of the float/double will be copied in BigDecimal.
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// Prefer the String constructor when you need an exact value.
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// Prefer the String constructor when you need an exact value.
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BigDecimal tenCents = new BigDecimal("0.1");
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BigDecimal tenCents = new BigDecimal("0.1");
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// Strings
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// Strings
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String fooString = "My String Is Here!";
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String fooString = "My String Is Here!";
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@ -184,7 +184,7 @@ public class LearnJava {
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intArray[1] = 1;
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intArray[1] = 1;
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System.out.println("intArray @ 1: " + intArray[1]); // => 1
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System.out.println("intArray @ 1: " + intArray[1]); // => 1
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// Others to check out
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// Other data types worth checking out
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// ArrayLists - Like arrays except more functionality is offered, and
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// ArrayLists - Like arrays except more functionality is offered, and
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// the size is mutable.
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// the size is mutable.
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// LinkedLists - Implementation of doubly-linked list. All of the
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// LinkedLists - Implementation of doubly-linked list. All of the
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@ -212,7 +212,7 @@ public class LearnJava {
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System.out.println("1+2 = " + (i1 + i2)); // => 3
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System.out.println("1+2 = " + (i1 + i2)); // => 3
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System.out.println("2-1 = " + (i2 - i1)); // => 1
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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("2*1 = " + (i2 * i1)); // => 2
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System.out.println("1/2 = " + (i1 / i2)); // => 0 (int/int returns an int)
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System.out.println("1/2 = " + (i1 / i2)); // => 0 (int/int returns int)
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System.out.println("1/2 = " + (i1 / (double)i2)); // => 0.5
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System.out.println("1/2 = " + (i1 / (double)i2)); // => 0.5
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// Modulo
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// Modulo
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@ -242,7 +242,7 @@ public class LearnJava {
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| Bitwise inclusive OR
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| Bitwise inclusive OR
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*/
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*/
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// Incrementations
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// Increment operators
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int i = 0;
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int i = 0;
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System.out.println("\n->Inc/Dec-rementation");
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System.out.println("\n->Inc/Dec-rementation");
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// The ++ and -- operators increment and decrement by 1 respectively.
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// The ++ and -- operators increment and decrement by 1 respectively.
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@ -314,7 +314,6 @@ public class LearnJava {
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// for each loop structure => for (<object> : <iterable>)
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// for each loop structure => for (<object> : <iterable>)
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// reads as: for each element in the iterable
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// reads as: for each element in the iterable
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// note: the object type must match the element type of the iterable.
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// note: the object type must match the element type of the iterable.
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for (int bar : fooList) {
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for (int bar : fooList) {
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System.out.println(bar);
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System.out.println(bar);
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//Iterates 9 times and prints 1-9 on new lines
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//Iterates 9 times and prints 1-9 on new lines
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@ -364,7 +363,6 @@ public class LearnJava {
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String bar = (foo < 10) ? "A" : "B";
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String bar = (foo < 10) ? "A" : "B";
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System.out.println(bar); // Prints A, because the statement is true
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System.out.println(bar); // Prints A, because the statement is true
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////////////////////////////////////////
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////////////////////////////////////////
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// Converting Data Types And Typecasting
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// Converting Data Types And Typecasting
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////////////////////////////////////////
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////////////////////////////////////////
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@ -387,7 +385,6 @@ public class LearnJava {
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// with some more intermediate concepts. Feel free to check it out here:
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// with some more intermediate concepts. Feel free to check it out here:
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// http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
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// http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
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///////////////////////////////////////
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///////////////////////////////////////
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// Classes And Functions
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// Classes And Functions
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///////////////////////////////////////
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///////////////////////////////////////
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@ -409,7 +406,6 @@ public class LearnJava {
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// Double Brace Initialization
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// Double Brace Initialization
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// The Java Language has no syntax for how to create static Collections
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// The Java Language has no syntax for how to create static Collections
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// in an easy way. Usually you end up in the following way:
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// in an easy way. Usually you end up in the following way:
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private static final Set<String> COUNTRIES = new HashSet<String>();
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private static final Set<String> COUNTRIES = new HashSet<String>();
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static {
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static {
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validCodes.add("DENMARK");
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validCodes.add("DENMARK");
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@ -420,7 +416,6 @@ public class LearnJava {
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// But there's a nifty way to achieve the same thing in an
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// But there's a nifty way to achieve the same thing in an
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// easier way, by using something that is called Double Brace
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// easier way, by using something that is called Double Brace
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// Initialization.
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// Initialization.
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private static final Set<String> COUNTRIES = new HashSet<String>() {{
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private static final Set<String> COUNTRIES = new HashSet<String>() {{
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add("DENMARK");
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add("DENMARK");
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add("SWEDEN");
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add("SWEDEN");
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@ -436,11 +431,9 @@ public class LearnJava {
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} // End main method
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} // End main method
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} // End LearnJava class
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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 not good practice. Instead split classes into separate files.
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// but it is not good practice. Instead split classes into separate files.
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// Class Declaration Syntax:
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// Class Declaration Syntax:
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// <public/private/protected> class <class name> {
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// <public/private/protected> class <class name> {
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// // data fields, constructors, functions all inside.
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// // data fields, constructors, functions all inside.
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@ -454,7 +447,6 @@ class Bicycle {
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private int speed; // Private: Only accessible from within the class
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private int speed; // Private: Only accessible from within the class
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protected int gear; // Protected: Accessible from the class and subclasses
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protected int gear; // Protected: Accessible from the class and subclasses
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String name; // default: Only accessible from within this package
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String name; // default: Only accessible from within this package
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static String className; // Static class variable
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static String className; // Static class variable
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// Static block
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// Static block
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@ -476,7 +468,6 @@ class Bicycle {
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speed = 5;
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speed = 5;
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name = "Bontrager";
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name = "Bontrager";
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}
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}
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// This is a constructor that takes arguments
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// This is a constructor that takes arguments
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public Bicycle(int startCadence, int startSpeed, int startGear,
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public Bicycle(int startCadence, int startSpeed, int startGear,
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String name) {
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String name) {
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@ -501,23 +492,18 @@ class Bicycle {
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public void setCadence(int newValue) {
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public void setCadence(int newValue) {
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cadence = newValue;
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cadence = newValue;
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}
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}
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public void setGear(int newValue) {
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public void setGear(int newValue) {
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gear = newValue;
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gear = newValue;
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}
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}
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public void speedUp(int increment) {
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public void speedUp(int increment) {
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speed += increment;
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speed += increment;
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}
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}
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public void slowDown(int decrement) {
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public void slowDown(int decrement) {
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speed -= decrement;
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speed -= decrement;
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}
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}
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public void setName(String newName) {
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public void setName(String newName) {
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name = newName;
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name = newName;
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}
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}
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public String getName() {
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public String getName() {
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return name;
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return name;
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}
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}
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@ -566,10 +552,8 @@ 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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}
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// We can now create a class that implements both of these interfaces.
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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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public class Fruit implements Edible, Digestible {
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@Override
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@Override
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public void eat() {
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public void eat() {
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// ...
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// ...
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@ -585,7 +569,6 @@ public class Fruit implements Edible, Digestible {
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// interfaces. For example:
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// interfaces. For example:
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public class ExampleClass extends ExampleClassParent implements InterfaceOne,
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public class ExampleClass extends ExampleClassParent implements InterfaceOne,
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InterfaceTwo {
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InterfaceTwo {
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|
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@Override
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@Override
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public void InterfaceOneMethod() {
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public void InterfaceOneMethod() {
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}
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}
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@ -604,14 +587,13 @@ public class ExampleClass extends ExampleClassParent implements InterfaceOne,
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// // Method declarations
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// // Method declarations
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// }
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// }
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// Marking a class as abstract means that it contains abstract methods that must
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// Marking a class as abstract means that it contains abstract methods that
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// be defined in a child class. Similar to interfaces, abstract classes cannot
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// must be defined in a child class. Similar to interfaces, abstract classes
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// be instantiated, but instead must be extended and the abstract methods
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// cannot be instantiated, but instead must be extended and the abstract
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// defined. Different from interfaces, abstract classes can contain a mixture of
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// methods defined. Different from interfaces, abstract classes can contain a
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// concrete and abstract methods. Methods in an interface cannot have a body,
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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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// mixture of unless the method is static, and variables are final by default,
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// abstract class. Also abstract classes CAN have the "main" method.
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// unlike an abstract class. Also abstract classes CAN have the "main" method.
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public abstract class Animal
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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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@ -656,7 +638,7 @@ class Dog extends Animal
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// @Override annotation here, since java doesn't allow
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// @Override annotation here, since java doesn't allow
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// overriding of static methods.
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// overriding of static methods.
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// What is happening here is called METHOD HIDING.
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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/
|
// Check out this SO post: http://stackoverflow.com/questions/16313649/
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public static void main(String[] args)
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public static void main(String[] args)
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{
|
{
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Dog pluto = new Dog();
|
Dog pluto = new Dog();
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@ -695,33 +677,29 @@ public abstract class Mammal()
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// Final Method Syntax:
|
// Final Method Syntax:
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// <access modifier> final <return type> <function name>(<args>)
|
// <access modifier> final <return type> <function name>(<args>)
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|
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// Final methods, like, final classes cannot be overridden by a child class,
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// Final methods, like, final classes cannot be overridden by a child
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// and are therefore the final implementation of the method.
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// class, and are therefore the final implementation of the method.
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public final boolean isWarmBlooded()
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public final boolean isWarmBlooded()
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{
|
{
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return true;
|
return true;
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}
|
}
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}
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}
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|
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|
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// Enum Type
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// Enum Type
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//
|
//
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// An enum type is a special data type that enables for a variable to be a set
|
// An enum type is a special data type that enables for a variable to be a set
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// of predefined constants. The variable must be equal to one of the values that
|
// of predefined constants. The variable must be equal to one of the values
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// have been predefined for it. Because they are constants, the names of an enum
|
// that have been predefined for it. Because they are constants, the names of
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// type's fields are in uppercase letters. In the Java programming language, you
|
// an enum type's fields are in uppercase letters. In the Java programming
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// define an enum type by using the enum keyword. For example, you would specify
|
// language, you define an enum type by using the enum keyword. For example,
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// a days-of-the-week enum type as:
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// you would specify a days-of-the-week enum type as:
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|
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public enum Day {
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public enum Day {
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SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
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SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
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THURSDAY, FRIDAY, SATURDAY
|
THURSDAY, FRIDAY, SATURDAY
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}
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}
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|
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// We can use our enum Day like that:
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// We can use our enum Day like that:
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|
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public class EnumTest {
|
public class EnumTest {
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|
|
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// Variable Enum
|
// Variable Enum
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Day day;
|
Day day;
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|
|
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@ -734,16 +712,13 @@ public class EnumTest {
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case MONDAY:
|
case MONDAY:
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System.out.println("Mondays are bad.");
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System.out.println("Mondays are bad.");
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break;
|
break;
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|
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case FRIDAY:
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case FRIDAY:
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System.out.println("Fridays are better.");
|
System.out.println("Fridays are better.");
|
||||||
break;
|
break;
|
||||||
|
|
||||||
case SATURDAY:
|
case SATURDAY:
|
||||||
case SUNDAY:
|
case SUNDAY:
|
||||||
System.out.println("Weekends are best.");
|
System.out.println("Weekends are best.");
|
||||||
break;
|
break;
|
||||||
|
|
||||||
default:
|
default:
|
||||||
System.out.println("Midweek days are so-so.");
|
System.out.println("Midweek days are so-so.");
|
||||||
break;
|
break;
|
||||||
@ -793,7 +768,6 @@ The links provided here below are just to get an understanding of the topic, fee
|
|||||||
|
|
||||||
* [Codingbat.com](http://codingbat.com/java)
|
* [Codingbat.com](http://codingbat.com/java)
|
||||||
|
|
||||||
|
|
||||||
**Books**:
|
**Books**:
|
||||||
|
|
||||||
* [Head First Java](http://www.headfirstlabs.com/books/hfjava/)
|
* [Head First Java](http://www.headfirstlabs.com/books/hfjava/)
|
||||||
@ -802,4 +776,4 @@ The links provided here below are just to get an understanding of the topic, fee
|
|||||||
|
|
||||||
* [Objects First with Java](http://www.amazon.com/Objects-First-Java-Practical-Introduction/dp/0132492660)
|
* [Objects First with Java](http://www.amazon.com/Objects-First-Java-Practical-Introduction/dp/0132492660)
|
||||||
|
|
||||||
* [Java The Complete Reference](http://www.amazon.com/gp/product/0071606300)
|
* [Java The Complete Reference](http://www.amazon.com/gp/product/0071606300)
|
Loading…
Reference in New Issue
Block a user