面向对象程序设计之封装性、继承性、多态性

面向控制台的计算器一

package com.test.java.features1; import java.util.Scanner; /** * 计算器类 */
public class ComputingCounter { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); System.out.println("输入 stop 关闭计算器"); while (true) { System.out.println("请输入一个数"); String number = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("请输入一个运算符号"); String symbol = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("请输入一个数"); 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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代码都写在了一个main方法里，这是面向过程编程。

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面向控制台的计算器二

假如之后需求发生变化，须要写一个面向windows的计算器，计算器一的代码复用性不高；
因此，咱们把计算器一的代码封装为两部分——Client和Opration；Client只负责输入输出，Opration负责后台计算。
这样，若是真的需求变化，要求写一个面向windows的计算器，Opration部分的代码彻底是能够被复用的。

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("输入 stop 关闭计算器"); while (true) { System.out.println("请输入一个数"); String number = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("请输入一个运算符号"); String symbol = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("请输入一个数"); 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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面向控制台的计算器三

如今咱们只支持加、减、乘、除，可是之后可能须要扩展其它的运算，好比x的y次方。
因此把可能发生变化的部分再次封装，分别封装为加法类、减法类、乘法类、除法类，并让它们共同继承Opration类，也就是定义了一个算法族；并使用简单工厂模式建立具体的类而返回抽象类型（多态）

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("输入 stop 关闭计算器"); while (true) { System.out.println("请输入一个数"); String number = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("请输入一个运算符号"); String symbol = scanner.nextLine(); if (number.equals("stop")) { break;} System.out.println("请输入一个数"); 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

总结：面向对象三大特征，封装性、继承性、多态性。有利于程序的复用性、可扩展性、维护性。