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[java/fa] delete (#4967)
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parent
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@ -1,901 +0,0 @@
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---
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language: java
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lang: fa-ir
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contributors:
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- ["Jake Prather", "https://github.com/JakeHP"]
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- ["Jakukyo Friel", "https://weakish.github.io"]
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- ["Madison Dickson", "https://github.com/mix3d"]
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- ["Simon Morgan", "https://sjm.io/"]
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- ["Zachary Ferguson", "https://github.com/zfergus2"]
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- ["Cameron Schermerhorn", "https://github.com/cschermerhorn"]
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- ["Rachel Stiyer", "https://github.com/rstiyer"]
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- ["Michael Dähnert", "https://github.com/JaXt0r"]
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- ["Rob Rose", "https://github.com/RobRoseKnows"]
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- ["Sean Nam", "https://github.com/seannam"]
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translators:
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- ["ghaseminya", "https://github.com/ghaseminya"]
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filename: LearnJava-fa.java
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---
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جاوا یک زبان برنامه نویسی کامپیوتری چند منظوره، با قابلیت همزمانی، برپایه کلاس و شی گرایی می باشد.
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[مطالعه بیشتر.](https://docs.oracle.com/javase/tutorial/java/)
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```java
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// Single-line comments start with //
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/*
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Multi-line comments look like this.
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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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* attributes of a Class.
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* Main attributes:
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*
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* @author @ghaseminya
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* @version v1.0
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*/
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// Import ArrayList class inside of the java.util package
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import java.util.ArrayList;
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// Import all classes inside of java.security package
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import java.security.*;
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// Each .java file contains one outer-level public class, with the same name
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// as the file.
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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
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// point.
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public static void main (String[] args) {
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///////////////////////////////////////
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// Input/Output
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///////////////////////////////////////
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/*
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* Output
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*/
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// Use System.out.println() to print lines.
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System.out.println("Hello World!");
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System.out.println(
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"Integer: " + 10 +
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" Double: " + 3.14 +
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" Boolean: " + true);
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// To print without a newline, use System.out.print().
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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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* Input
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*/
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// use Scanner to read input
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// must import java.util.Scanner;
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Scanner scanner = new Scanner(System.in);
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// read string input
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String name = scanner.next();
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// read byte input
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byte numByte = scanner.nextByte();
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// read int input
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int numInt = scanner.nextInt();
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// read long input
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float numFloat - scanner.nextFloat();
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// read double input
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double numDouble = scanner.nextDouble();
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// read boolean input
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boolean bool = scanner.nextBoolean();
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///////////////////////////////////////
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// Variables
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///////////////////////////////////////
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/*
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* Variable Declaration
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*/
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// Declare a variable using <type> <name>
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int fooInt;
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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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/*
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* Variable Initialization
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*/
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// Initialize a variable using <type> <name> = <val>
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int barInt = 1;
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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 barInt1, barInt2, barInt3;
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barInt1 = barInt2 = barInt3 = 1;
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/*
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* Variable types
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*/
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// Byte - 8-bit signed two's complement integer
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// (-128 <= byte <= 127)
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byte fooByte = 100;
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// If you would like to interpret a byte as an unsigned integer
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// then this simple operation can help
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int unsignedIntLessThan256 = 0xff & fooByte;
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// this contrasts a cast which can be negative.
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int signedInt = (int) fooByte;
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// Short - 16-bit signed two's complement integer
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// (-32,768 <= short <= 32,767)
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short fooShort = 10000;
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// Integer - 32-bit signed two's complement integer
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// (-2,147,483,648 <= int <= 2,147,483,647)
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int bazInt = 1;
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// Long - 64-bit signed two's complement integer
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// (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807)
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long fooLong = 100000L;
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// L is used to denote that this variable value is of type Long;
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// anything without is treated as integer by default.
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// Note: byte, short, int and long are signed. They can have positive and negative values.
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// There are no unsigned variants.
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// char, however, is 16-bit unsigned.
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// Float - Single-precision 32-bit IEEE 754 Floating Point
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// 2^-149 <= float <= (2-2^-23) * 2^127
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float fooFloat = 234.5f;
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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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// 2^-1074 <= x <= (2-2^-52) * 2^1023
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double fooDouble = 123.4;
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// Boolean - true & false
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boolean fooBoolean = true;
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boolean barBoolean = false;
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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 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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// BigInteger - Immutable arbitrary-precision integers
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//
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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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// of bytes and are manipulated using functions built into BigInteger
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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 fooBigInteger = new BigInteger(fooByteArray);
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// BigDecimal - Immutable, arbitrary-precision signed decimal number
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//
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// A BigDecimal takes two parts: an arbitrary precision integer
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// unscaled value and a 32-bit integer scale
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//
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// BigDecimal allows the programmer complete control over decimal
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// rounding. It is recommended to use BigDecimal with currency values
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// and where exact decimal precision is required.
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//
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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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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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// 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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BigDecimal tenCents = new BigDecimal("0.1");
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// Strings
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String fooString = "My String Is Here!";
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// \n is an escaped character that starts a new line
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String barString = "Printing on a new line?\nNo Problem!";
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// \t is an escaped character that adds a tab character
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String bazString = "Do you want to add a tab?\tNo Problem!";
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System.out.println(fooString);
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System.out.println(barString);
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System.out.println(bazString);
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// String Building
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// #1 - with plus operator
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// That's the basic way to do it (optimized under the hood)
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String plusConcatenated = "Strings can " + "be concatenated " + "via + operator.";
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System.out.println(plusConcatenated);
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// Output: Strings can be concatenated via + operator.
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// #2 - with StringBuilder
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// This way doesn't create any intermediate strings. It just stores the string pieces, and ties them together
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// when toString() is called.
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// Hint: This class is not thread safe. A thread-safe alternative (with some impact on performance) is StringBuffer.
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StringBuilder builderConcatenated = new StringBuilder();
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builderConcatenated.append("You ");
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builderConcatenated.append("can use ");
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builderConcatenated.append("the StringBuilder class.");
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System.out.println(builderConcatenated.toString()); // only now is the string built
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// Output: You can use the StringBuilder class.
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// StringBuilder is efficient when the fully constructed String is not required until the end of some processing.
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StringBuilder stringBuilder = new StringBuilder();
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String inefficientString = "";
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for(int i = 0 ; i < 10; i++){
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stringBuilder.append(i).append(" ");
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inefficientString += i + " ";
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}
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System.out.println(inefficientString);
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System.out.println(stringBuilder.toString());
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// inefficientString requires a lot more work to produce, as it generates a String on every loop iteration.
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// Simple concatenation with + is compiled to a StringBuilder and toString()
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// Avoid string concatenation in loops.
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// #3 - with String formatter
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// Another alternative way to create strings. Fast and readable.
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String.format("%s may prefer %s.", "Or you", "String.format()");
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// Output: Or you may prefer String.format().
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// Arrays
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// The array size must be decided upon instantiation
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// The following formats work for declaring an array
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// <datatype>[] <var name> = new <datatype>[<array size>];
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// <datatype> <var name>[] = new <datatype>[<array size>];
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int[] intArray = new int[10];
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String[] stringArray = new String[1];
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boolean boolArray[] = new boolean[100];
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// Another way to declare & initialize an array
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int[] y = {9000, 1000, 1337};
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String names[] = {"Bob", "John", "Fred", "Juan Pedro"};
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boolean bools[] = {true, false, false};
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// Indexing an array - Accessing an element
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System.out.println("intArray @ 0: " + intArray[0]);
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// Arrays are zero-indexed and mutable.
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intArray[1] = 1;
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System.out.println("intArray @ 1: " + intArray[1]); // => 1
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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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// the size is mutable.
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// LinkedLists - Implementation of doubly-linked list. All of the
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// operations perform as could be expected for a
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// doubly-linked list.
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// Maps - A set of objects that map keys to values. Map is
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// an interface and therefore cannot be instantiated.
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// The type of keys and values contained in a Map must
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// be specified upon instantiation of the implementing
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// class. Each key may map to only one corresponding value,
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// and each key may appear only once (no duplicates).
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// HashMaps - This class uses a hashtable to implement the Map
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// interface. This allows the execution time of basic
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// operations, such as get and insert element, to remain
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// constant even for large sets.
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// TreeMap - This class is a sorted tree structure. It implements a red
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// black tree and sorts the entries based on the key value or
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// the comparator provided while creating the object
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///////////////////////////////////////
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// Operators
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///////////////////////////////////////
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System.out.println("\n->Operators");
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int i1 = 1, i2 = 2; // Shorthand for multiple declarations
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// Arithmetic is straightforward
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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)); // => 2
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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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// Modulo
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System.out.println("11%3 = "+(11 % 3)); // => 2
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// Comparison operators
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System.out.println("3 == 2? " + (3 == 2)); // => false
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System.out.println("3 != 2? " + (3 != 2)); // => true
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System.out.println("3 > 2? " + (3 > 2)); // => true
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System.out.println("3 < 2? " + (3 < 2)); // => false
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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/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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*/
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// Increment operators
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int i = 0;
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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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// If they are placed before the variable, they increment then return;
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// after the variable they return then increment.
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System.out.println(i++); // i = 1, prints 0 (post-increment)
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System.out.println(++i); // i = 2, prints 2 (pre-increment)
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System.out.println(i--); // i = 1, prints 2 (post-decrement)
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System.out.println(--i); // i = 0, prints 0 (pre-decrement)
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///////////////////////////////////////
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// Control Structures
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///////////////////////////////////////
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System.out.println("\n->Control Structures");
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// If statements are c-like
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int j = 10;
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if (j == 10) {
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System.out.println("I get printed");
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} else if (j > 10) {
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System.out.println("I don't");
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} else {
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System.out.println("I also don't");
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}
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// While loop
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int fooWhile = 0;
|
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while(fooWhile < 100) {
|
||||
System.out.println(fooWhile);
|
||||
// Increment the counter
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||||
// Iterated 100 times, fooWhile 0,1,2...99
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fooWhile++;
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}
|
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System.out.println("fooWhile Value: " + fooWhile);
|
||||
|
||||
// Do While Loop
|
||||
int fooDoWhile = 0;
|
||||
do {
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System.out.println(fooDoWhile);
|
||||
// Increment the counter
|
||||
// Iterated 99 times, fooDoWhile 0->99
|
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fooDoWhile++;
|
||||
} while(fooDoWhile < 100);
|
||||
System.out.println("fooDoWhile Value: " + fooDoWhile);
|
||||
|
||||
// For Loop
|
||||
// for loop structure => for(<start_statement>; <conditional>; <step>)
|
||||
for (int fooFor = 0; fooFor < 10; fooFor++) {
|
||||
System.out.println(fooFor);
|
||||
// Iterated 10 times, fooFor 0->9
|
||||
}
|
||||
System.out.println("fooFor Value: " + fooFor);
|
||||
|
||||
// Nested For Loop Exit with Label
|
||||
outer:
|
||||
for (int i = 0; i < 10; i++) {
|
||||
for (int j = 0; j < 10; j++) {
|
||||
if (i == 5 && j ==5) {
|
||||
break outer;
|
||||
// breaks out of outer loop instead of only the inner one
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// For Each Loop
|
||||
// The for loop is also able to iterate over arrays as well as objects
|
||||
// that implement the Iterable interface.
|
||||
int[] fooList = {1, 2, 3, 4, 5, 6, 7, 8, 9};
|
||||
// for each loop structure => for (<object> : <iterable>)
|
||||
// reads as: for each element in the iterable
|
||||
// note: the object type must match the element type of the iterable.
|
||||
for (int bar : fooList) {
|
||||
System.out.println(bar);
|
||||
//Iterates 9 times and prints 1-9 on new lines
|
||||
}
|
||||
|
||||
// Switch Case
|
||||
// A switch works with the byte, short, char, and int data types.
|
||||
// It also works with enumerated types (discussed in Enum Types), the
|
||||
// String class, and a few special classes that wrap primitive types:
|
||||
// Character, Byte, Short, and Integer.
|
||||
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);
|
||||
|
||||
// Starting in Java 7 and above, switching Strings works like this:
|
||||
String myAnswer = "maybe";
|
||||
switch(myAnswer) {
|
||||
case "yes":
|
||||
System.out.println("You answered yes.");
|
||||
break;
|
||||
case "no":
|
||||
System.out.println("You answered no.");
|
||||
break;
|
||||
case "maybe":
|
||||
System.out.println("You answered maybe.");
|
||||
break;
|
||||
default:
|
||||
System.out.println("You answered " + myAnswer);
|
||||
break;
|
||||
}
|
||||
|
||||
|
||||
// Try-with-resources (Java 7+)
|
||||
// Try-catch-finally statements work as expected in Java but in Java 7+
|
||||
// the try-with-resources statement is also available. Try-with-resources
|
||||
// simplifies try-catch-finally statements be closing resources
|
||||
// automatically.
|
||||
|
||||
// In order to use a try-with-resources, include a an instance of a class
|
||||
// in the try statement. The class must implement java.lang.AutoCloseable.
|
||||
try(BufferedReader br = new BufferedReader(new FileReader("foo.txt"))) {
|
||||
// You can attempt to do something that could throw an exception.
|
||||
System.out.println(br.readLine());
|
||||
// In Java 7, the resource will always be closed, even if it throws
|
||||
// an Exception.
|
||||
} catch (Exception ex) {
|
||||
//The resource will be closed before the catch statement executes.
|
||||
System.out.println("readLine() failed.");
|
||||
}
|
||||
// No need for a finally statement in this case, the BufferedReader is
|
||||
// already closed. This can be used to avoid certain edge cases where
|
||||
// a finally statement might not be called.
|
||||
// To learn more:
|
||||
// https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html
|
||||
|
||||
|
||||
// Conditional Shorthand
|
||||
// You can use the '?' operator for quick assignments or logic forks.
|
||||
// Reads as "If (statement) is true, use <first value>, otherwise, use
|
||||
// <second value>"
|
||||
int foo = 5;
|
||||
String bar = (foo < 10) ? "A" : "B";
|
||||
System.out.println(bar); // Prints A, because the statement is true
|
||||
|
||||
////////////////////////////////////////
|
||||
// Converting Data Types And Typecasting
|
||||
////////////////////////////////////////
|
||||
|
||||
// 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:
|
||||
// https://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); // You should always use setter and getter methods
|
||||
trek.setCadence(100);
|
||||
|
||||
// toString returns this Object's string representation.
|
||||
System.out.println("trek info: " + trek.toString());
|
||||
|
||||
// Double Brace Initialization
|
||||
// The Java Language has no syntax for how to create static Collections
|
||||
// in an easy way. Usually you end up in the following way:
|
||||
private static final Set<String> COUNTRIES = new HashSet<String>();
|
||||
static {
|
||||
COUNTRIES.add("DENMARK");
|
||||
COUNTRIES.add("SWEDEN");
|
||||
COUNTRIES.add("FINLAND");
|
||||
}
|
||||
|
||||
// But there's a nifty way to achieve the same thing in an
|
||||
// easier way, by using something that is called Double Brace
|
||||
// Initialization.
|
||||
private static final Set<String> COUNTRIES = new HashSet<String>() {{
|
||||
add("DENMARK");
|
||||
add("SWEDEN");
|
||||
add("FINLAND");
|
||||
}}
|
||||
|
||||
// The first brace is creating a new AnonymousInnerClass and the
|
||||
// second one declares an instance initializer block. This block
|
||||
// is called when the anonymous inner class is created.
|
||||
// This does not only work for Collections, it works for all
|
||||
// non-final classes.
|
||||
|
||||
} // End main method
|
||||
} // End LearnJava class
|
||||
|
||||
// You can include other, non-public outer-level classes in a .java file,
|
||||
// but it is not good practice. Instead split classes into separate files.
|
||||
|
||||
// Class Declaration Syntax:
|
||||
// <public/private/protected> class <class name> {
|
||||
// // data fields, constructors, functions all inside.
|
||||
// // functions are called as methods in Java.
|
||||
// }
|
||||
|
||||
class Bicycle {
|
||||
|
||||
// Bicycle's Fields/Variables
|
||||
public int cadence; // Public: Can be accessed from anywhere
|
||||
private int speed; // Private: Only accessible from within the class
|
||||
protected int gear; // Protected: Accessible from the class and subclasses
|
||||
String name; // default: Only accessible from within this package
|
||||
static String className; // Static class variable
|
||||
|
||||
// Static block
|
||||
// Java has no implementation of static constructors, but
|
||||
// has a static block that can be used to initialize class variables
|
||||
// (static variables).
|
||||
// This block will be called when the class is loaded.
|
||||
static {
|
||||
className = "Bicycle";
|
||||
}
|
||||
|
||||
// Constructors are a way of creating classes
|
||||
// This is a constructor
|
||||
public Bicycle() {
|
||||
// You can also call another constructor:
|
||||
// this(1, 50, 5, "Bontrager");
|
||||
gear = 1;
|
||||
cadence = 50;
|
||||
speed = 5;
|
||||
name = "Bontrager";
|
||||
}
|
||||
// This is a constructor that takes arguments
|
||||
public Bicycle(int startCadence, int startSpeed, int startGear,
|
||||
String name) {
|
||||
this.gear = startGear;
|
||||
this.cadence = startCadence;
|
||||
this.speed = startSpeed;
|
||||
this.name = name;
|
||||
}
|
||||
|
||||
// Method Syntax:
|
||||
// <public/private/protected> <return type> <function name>(<args>)
|
||||
|
||||
// Java classes often implement getters and setters for their fields
|
||||
|
||||
// Method declaration syntax:
|
||||
// <access modifier> <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 void setName(String newName) {
|
||||
name = newName;
|
||||
}
|
||||
public String getName() {
|
||||
return name;
|
||||
}
|
||||
|
||||
//Method to display the attribute values of this Object.
|
||||
@Override // Inherited from the Object class.
|
||||
public String toString() {
|
||||
return "gear: " + gear + " cadence: " + cadence + " speed: " + speed +
|
||||
" name: " + name;
|
||||
}
|
||||
} // 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, "PennyFarthing");
|
||||
}
|
||||
|
||||
// You should mark a method you're overriding with an @annotation.
|
||||
// To learn more about what annotations are and their purpose check this
|
||||
// out: http://docs.oracle.com/javase/tutorial/java/annotations/
|
||||
@Override
|
||||
public void setGear(int gear) {
|
||||
this.gear = 0;
|
||||
}
|
||||
}
|
||||
|
||||
// Interfaces
|
||||
// Interface declaration syntax
|
||||
// <access-level> interface <interface-name> extends <super-interfaces> {
|
||||
// // Constants
|
||||
// // Method declarations
|
||||
// }
|
||||
|
||||
// Example - Food:
|
||||
public interface Edible {
|
||||
public void eat(); // Any class that implements this interface, must
|
||||
// implement this method.
|
||||
}
|
||||
|
||||
public interface Digestible {
|
||||
public void digest();
|
||||
// In Java 8, interfaces can have default method.
|
||||
// public void digest() {
|
||||
// System.out.println("digesting ...");
|
||||
// }
|
||||
}
|
||||
|
||||
// We can now create a class that implements both of these interfaces.
|
||||
public class Fruit implements Edible, Digestible {
|
||||
@Override
|
||||
public void eat() {
|
||||
// ...
|
||||
}
|
||||
|
||||
@Override
|
||||
public void digest() {
|
||||
// ...
|
||||
}
|
||||
}
|
||||
|
||||
// In Java, you can extend only one class, but you can implement many
|
||||
// interfaces. For example:
|
||||
public class ExampleClass extends ExampleClassParent implements InterfaceOne,
|
||||
InterfaceTwo {
|
||||
@Override
|
||||
public void InterfaceOneMethod() {
|
||||
}
|
||||
|
||||
@Override
|
||||
public void InterfaceTwoMethod() {
|
||||
}
|
||||
|
||||
}
|
||||
|
||||
// Abstract Classes
|
||||
|
||||
// Abstract Class declaration syntax
|
||||
// <access-level> abstract <abstract-class-name> extends <super-abstract-classes> {
|
||||
// // Constants and variables
|
||||
// // Method declarations
|
||||
// }
|
||||
|
||||
// Marking a class as abstract means that it contains abstract methods that
|
||||
// must be defined in a child class. Similar to interfaces, abstract classes
|
||||
// cannot be instantiated, but instead must be extended and the abstract
|
||||
// methods defined. Different from interfaces, abstract classes can contain a
|
||||
// concrete and abstract methods. Methods in an interface cannot have a body,
|
||||
// mixture of unless the method is static, and variables are final by default,
|
||||
// unlike an abstract class. Also abstract classes CAN have the "main" method.
|
||||
public abstract class Animal
|
||||
{
|
||||
public abstract void makeSound();
|
||||
|
||||
// Method can have a body
|
||||
public void eat()
|
||||
{
|
||||
System.out.println("I am an animal and I am Eating.");
|
||||
// Note: We can access private variable here.
|
||||
age = 30;
|
||||
}
|
||||
|
||||
// No need to initialize, however in an interface
|
||||
// a variable is implicitly final and hence has
|
||||
// to be initialized.
|
||||
protected int age;
|
||||
|
||||
public void printAge()
|
||||
{
|
||||
System.out.println(age);
|
||||
}
|
||||
|
||||
// Abstract classes can have main function.
|
||||
public static void main(String[] args)
|
||||
{
|
||||
System.out.println("I am abstract");
|
||||
}
|
||||
}
|
||||
|
||||
class Dog extends Animal
|
||||
{
|
||||
// Note still have to override the abstract methods in the
|
||||
// abstract class.
|
||||
@Override
|
||||
public void makeSound()
|
||||
{
|
||||
System.out.println("Bark");
|
||||
// age = 30; ==> ERROR! age is private to Animal
|
||||
}
|
||||
|
||||
// NOTE: You will get an error if you used the
|
||||
// @Override annotation here, since java doesn't allow
|
||||
// overriding of static methods.
|
||||
// What is happening here is called METHOD HIDING.
|
||||
// Check out this SO post: http://stackoverflow.com/questions/16313649/
|
||||
public static void main(String[] args)
|
||||
{
|
||||
Dog pluto = new Dog();
|
||||
pluto.makeSound();
|
||||
pluto.eat();
|
||||
pluto.printAge();
|
||||
}
|
||||
}
|
||||
|
||||
// Final Classes
|
||||
|
||||
// Final Class declaration syntax
|
||||
// <access-level> final <final-class-name> {
|
||||
// // Constants and variables
|
||||
// // Method declarations
|
||||
// }
|
||||
|
||||
// Final classes are classes that cannot be inherited from and are therefore a
|
||||
// final child. In a way, final classes are the opposite of abstract classes
|
||||
// because abstract classes must be extended, but final classes cannot be
|
||||
// extended.
|
||||
public final class SaberToothedCat extends Animal
|
||||
{
|
||||
// Note still have to override the abstract methods in the
|
||||
// abstract class.
|
||||
@Override
|
||||
public void makeSound()
|
||||
{
|
||||
System.out.println("Roar");
|
||||
}
|
||||
}
|
||||
|
||||
// Final Methods
|
||||
public abstract class Mammal()
|
||||
{
|
||||
// Final Method Syntax:
|
||||
// <access modifier> final <return type> <function name>(<args>)
|
||||
|
||||
// Final methods, like, final classes cannot be overridden by a child
|
||||
// class, and are therefore the final implementation of the method.
|
||||
public final boolean isWarmBlooded()
|
||||
{
|
||||
return true;
|
||||
}
|
||||
}
|
||||
|
||||
// Enum Type
|
||||
//
|
||||
// An enum type is a special data type that enables for a variable to be a set
|
||||
// of predefined constants. The variable must be equal to one of the values
|
||||
// that have been predefined for it. Because they are constants, the names of
|
||||
// an enum type's fields are in uppercase letters. In the Java programming
|
||||
// language, you define an enum type by using the enum keyword. For example,
|
||||
// you would specify a days-of-the-week enum type as:
|
||||
public enum Day {
|
||||
SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
|
||||
THURSDAY, FRIDAY, SATURDAY
|
||||
}
|
||||
|
||||
// We can use our enum Day like that:
|
||||
public class EnumTest {
|
||||
// Variable Enum
|
||||
Day day;
|
||||
|
||||
public EnumTest(Day day) {
|
||||
this.day = day;
|
||||
}
|
||||
|
||||
public void tellItLikeItIs() {
|
||||
switch (day) {
|
||||
case MONDAY:
|
||||
System.out.println("Mondays are bad.");
|
||||
break;
|
||||
case FRIDAY:
|
||||
System.out.println("Fridays are better.");
|
||||
break;
|
||||
case SATURDAY:
|
||||
case SUNDAY:
|
||||
System.out.println("Weekends are best.");
|
||||
break;
|
||||
default:
|
||||
System.out.println("Midweek days are so-so.");
|
||||
break;
|
||||
}
|
||||
}
|
||||
|
||||
public static void main(String[] args) {
|
||||
EnumTest firstDay = new EnumTest(Day.MONDAY);
|
||||
firstDay.tellItLikeItIs(); // => Mondays are bad.
|
||||
EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
|
||||
thirdDay.tellItLikeItIs(); // => Midweek days are so-so.
|
||||
}
|
||||
}
|
||||
|
||||
// Enum types are much more powerful than we show above.
|
||||
// The enum body can include methods and other fields.
|
||||
// You can see more at https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
|
||||
```
|
||||
|
||||
## مطالب بیشتر
|
||||
|
||||
لینکهای زیر را می توانید برای پیگیرهای بیشتر استفاده کنید.
|
||||
البته همیشه گوگل را در کنار دستتان داشته باشید!
|
||||
|
||||
**سایت های راهنمای اصلی**:
|
||||
|
||||
* [Java Tutorial Trail from Sun / Oracle](https://docs.oracle.com/javase/tutorial/index.html)
|
||||
|
||||
* [Java Access level modifiers](https://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html)
|
||||
|
||||
* [Object-Oriented Programming Concepts](https://docs.oracle.com/javase/tutorial/java/concepts/index.html):
|
||||
* [Inheritance](https://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html)
|
||||
* [Polymorphism](https://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html)
|
||||
* [Abstraction](https://docs.oracle.com/javase/tutorial/java/IandI/abstract.html)
|
||||
|
||||
* [Exceptions](https://docs.oracle.com/javase/tutorial/essential/exceptions/index.html)
|
||||
|
||||
* [Interfaces](https://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html)
|
||||
|
||||
* [Generics](https://docs.oracle.com/javase/tutorial/java/generics/index.html)
|
||||
|
||||
* [Java Code Conventions](https://www.oracle.com/technetwork/java/codeconvtoc-136057.html)
|
||||
|
||||
* New features in Java 8:
|
||||
* [Lambda expressions (functional programming)](https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html)
|
||||
* [Date and time API (java.time package)](http://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html)
|
||||
|
||||
**راهنما و سایت های آموزشی**
|
||||
|
||||
* [Learneroo.com - Learn Java](http://www.learneroo.com)
|
||||
|
||||
* [Codingbat.com](http://codingbat.com/java)
|
||||
|
||||
**کتابها**:
|
||||
|
||||
* [Head First Java](http://www.headfirstlabs.com/books/hfjava/)
|
||||
|
||||
* [Thinking in Java](https://www.amazon.com/Thinking-Java-4th-Bruce-Eckel/dp/0131872486/)
|
||||
|
||||
* [Objects First with Java](https://www.amazon.com/Objects-First-Java-Practical-Introduction/dp/0132492660)
|
||||
|
||||
* [Java The Complete Reference](https://www.amazon.com/gp/product/0071606300)
|
Loading…
Reference in New Issue
Block a user