面向對象程序設計之封裝性、繼承性、多態性

面向控制檯的計算器一

package com.test.java.features1; import java.util.Scanner; /** * 計算器類 */
public class ComputingCounter { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); System.out.println("輸入 stop 關閉計算器"); while (true) { System.out.println("請輸入一個數"); String number = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("請輸入一個運算符號"); String symbol = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("請輸入一個數"); String number2 = scanner.nextLine(); if (number.equals("stop")) { break;} compute(Double.parseDouble(number), Double.parseDouble(number2), symbol); } scanner.close(); } private static void compute(double number, double number2, String symbol) { switch (symbol) { case "+": System.out.println((number + number2)); break; case "-": System.out.println((number - number2)); break; case "*": System.out.println((number * number2)); break; case "/": System.out.println((number / number2)); break; } } }

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代碼都寫在了一個main方法裏，這是面向過程編程。

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面向控制檯的計算器二

假如之後需求發生變化，須要寫一個面向windows的計算器，計算器一的代碼複用性不高；
因此，咱們把計算器一的代碼封裝爲兩部分——Client和Opration；Client只負責輸入輸出，Opration負責後臺計算。
這樣，若是真的需求變化，要求寫一個面向windows的計算器，Opration部分的代碼徹底是能夠被複用的。

package com.test.java.features2; import com.test.java.features2.Opration; import java.util.Scanner; public class Client { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); System.out.println("輸入 stop 關閉計算器"); while (true) { System.out.println("請輸入一個數"); String number = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("請輸入一個運算符號"); String symbol = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("請輸入一個數"); String number2 = scanner.nextLine(); if (number.equals("stop")) { break;} Opration.compute(Double.parseDouble(number), Double.parseDouble(number2), symbol); } scanner.close(); } }

Client.java

package com.test.java.features2; public class Opration { public static void compute(double number, double number2, String symbol) { switch (symbol) { case "+": System.out.println((number + number2)); break; case "-": System.out.println((number - number2)); break; case "*": System.out.println((number * number2)); break; case "/": System.out.println((number / number2)); } } }

Opration.java

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面向控制檯的計算器三

如今咱們只支持加、減、乘、除，可是之後可能須要擴展其它的運算，好比x的y次方。
因此把可能發生變化的部分再次封裝，分別封裝爲加法類、減法類、乘法類、除法類，並讓它們共同繼承Opration類，也就是定義了一個算法族；並使用簡單工廠模式建立具體的類而返回抽象類型（多態）

package com.test.java.features3; import java.util.Scanner; public class Client { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); System.out.println("輸入 stop 關閉計算器"); while (true) { System.out.println("請輸入一個數"); String number = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("請輸入一個運算符號"); String symbol = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("請輸入一個數"); String number2 = scanner.nextLine(); if (number.equals("stop")) { break;} Opration.passOn(Double.parseDouble(number), Double.parseDouble(number2), symbol); } scanner.close(); } }

Client.java

package com.test.java.features3; public abstract class Opration { public static void passOn(double number, double number2, String symbol) { Opration opratoin = OprationFactory.getOpratoin(symbol); opratoin.compute(number, number2); } public abstract void compute(double number, double number2); }

Opration.java

package com.test.java.features3; public class Add extends Opration { @Override public void compute(double number, double number2) { System.out.println((number + number2)); } }

Add.java

package com.test.java.features3; public class Sub extends Opration{ @Override public void compute(double number, double number2) { System.out.println((number - number2)); } }

Sub.java

package com.test.java.features3; public class Multiply extends Opration { @Override public void compute(double number, double number2) { System.out.println((number * number2)); } }

Multiply.java

package com.test.java.features3; public class Divide extends Opration { @Override public void compute(double number, double number2) { System.out.println((number / number2)); } }

Divide.java

package com.test.java.features3; public class OprationFactory { public static Opration getOpratoin(String symbol) { switch (symbol) { case "+": return new Add(); case "-": return new Sub(); case "*": return new Multiply(); case "/": return new Divide(); } return null; } }

OprationFactory.java

總結：面向對象三大特徵，封裝性、繼承性、多態性。有利於程序的複用性、可擴展性、維護性。