1 這里是一個計算器,運算規則為 加減乘除,輸出相應的結果

2?UML圖

3 ?java類

Counter.java ?(抽象接口)

package DesignPattern.calculator;public interface Counter {public double getResult(); }

AddCounter.java (加法類)

package DesignPattern.calculator;public class AddCounter implements Counter {private double x;private double y;public AddCounter(double x,double y){this.x = x;this.y = y;}@Overridepublic double getResult() {return this.x + this.y;}}
DivCounter.java (減法類)

package DesignPattern.calculator;public class DivCounter implements Counter {private double x;private double y;public DivCounter(double x,double y){this.x = x;this.y = y;}@Overridepublic double getResult() {return this.x - this.y;}}

MulCounter.java (乘法類)

package DesignPattern.calculator;public class MulCounter implements Counter {private double x;private double y;public MulCounter(double x,double y){this.x = x;this.y = y;}@Overridepublic double getResult() {return this.x * this.y;}}
SubCounter.java (除法類)
package DesignPattern.calculator;public class SubCounter implements Counter {private double x;private double y;public SubCounter(double x,double y){this.x = x;this.y = y;}@Overridepublic double getResult() {double result = 0;if(this.y == 0){try {throw new MyException("被除數為0");} catch (MyException e) {// TODO Auto-generated catch blocke.printStackTrace();}}else{result = this.x/this.y;}return result;}}
ErrorCounter.java (未知規則,如果客戶端傳錯了類型,則調用該類)

package DesignPattern.calculator;public class ErrorCounter implements Counter {private double x;private double y;public ErrorCounter(double x,double y){this.x = x;this.y = y;}@Overridepublic double getResult() {try {throw new MyException("異常:錯誤的計算類");} catch (MyException e) {// TODO Auto-generated catch blocke.printStackTrace();}return 0;}}

MyException.java (自定義異常類,處理異常)
package DesignPattern.calculator;public class MyException extends Exception {public MyException(String str){System.out.println(str);} }

Client.java (客戶端)

package DesignPattern.calculator;public class Client {public static void main(String[] args) {double x = 10,y =20;Counter Counter;// 加法Counter = Factory.createCounter('+', x, y);System.out.println("加法結果為 : " + Counter.getResult());//減法Counter = Factory.createCounter('-', x, y);System.out.println("減法的結果為 : " + Counter.getResult());//乘法Counter = Factory.createCounter('*', x, y);System.out.println("乘法的結果為 : " + Counter.getResult());//除法Counter = Factory.createCounter('/', x, y);System.out.println("除法的結果為 : " + Counter.getResult());//除法 ,被除數為0Counter = Factory.createCounter('/', x, 0);System.out.println("除法的結果為 : " + Counter.getResult());//未知Counter = Factory.createCounter('?', x, y);System.out.println("未知規則的結果 : " + Counter.getResult());}}

4 輸出結果

總結

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