简单工厂模式-Java篇

简单工厂模式就是考虑如何实例化对象的问题，就是说到底要实例化谁，将来会不会增加实例化对象，比如计算器类中增加开根元素，应该考虑用一个单独的类来创造实例的过程，这就是工厂。下面将利用计算器类举例，解释简单工厂模式：

1.运算符类：

 1 package com.lujie;
 2
 3 public class Operation {
 4     private double _numberA=0;
 5     private double _numberB=0;
 6
 7     public void set_numberA(double _numberA) {
 8         this._numberA = _numberA;
 9     }
10     public void set_numberB(double _numberB) {
11         this._numberB = _numberB;
12     }
13     public double get_numberA() {
14         return _numberA;
15     }
16     public double get_numberB() {
17         return _numberB;
18     }
19     public  double getResult()  {
20         double result=0;
21         return result;
22     }
23 }

2.利用继承和多态实现代码松耦合：

　　2.1加法类继承自运算符类:

 1 package com.lujie;
 2
 3 public class OperationAdd extends Operation{
 4
 5     public double getResult() {
 6         double result =0;
 7         result=this.get_numberA()+this.get_numberB();
 8         return result;
 9
10     }
11 }

　　2.2减法类继承自运算符类:

 1 package com.lujie;
 2
 3 public class OperationSub extends Operation{
 4
 5     public double getResult() {
 6         double result =0;
 7         result=this.get_numberA()-this.get_numberB();
 8         return result;
 9
10     }
11 }

　　2.3乘法类继承自运算符类:

 1 package com.lujie;
 2
 3 public class OperationMul extends Operation{
 4
 5     public double getResult()  {
 6         double result =0;
 7         if(this.get_numberB()==0)
 8         result=this.get_numberA()*this.get_numberB();
 9         return result;
10
11     }
12 }

　　2.4除法类继承自运算符类:

 1 package com.lujie;
 2
 3 public class OperationDiv extends Operation{
 4
 5     public double getResult()  {
 6         double result =0;
 7         try {
 8
 9             result=this.get_numberA()/this.get_numberB();
10
11         } catch (Exception e) {
12             System.out.println("除数不能为0！");
13         }
14
15         return result;
16     }
17 }

3.简单的运算工厂类：

 1 class OperationFactory{
 2     public static Operation createOperate(String operate) {
 3
 4         Operation oper=null;
 5         switch (operate) {
 6         case "+":
 7             oper=new OperationAdd();
 8             break;
 9         case "-":
10             oper=new OperationSub();
11             break;
12         case "*":
13             oper=new OperationMul();
14             break;
15         case "/":
16             oper=new OperationDiv();
17             break;
18         }
19
20         return oper;
21     }
22 }

4.工厂模式举例：

1 public static void main(String[] args)  {
2
3         Operation oper;
4         oper=OperationFactory.createOperate("/");
5         oper.set_numberA(1);
6         oper.set_numberB(0);
7         double result=oper.getResult();
8         System.out.println("结果为："+result);
9 }