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：

 package com.lujie;

 public class Operation {
     private double _numberA=0;
     private double _numberB=0;

     public void set_numberA(double _numberA) {
         this._numberA = _numberA;
     }
     public void set_numberB(double _numberB) {
         this._numberB = _numberB;
     }
     public double get_numberA() {
         return _numberA;
     }
     public double get_numberB() {
         return _numberB;
     }
     public  double getResult()  {
         double result=0;
         return result;
     }
 }

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:

 package com.lujie;

 public class OperationAdd extends Operation{

     public double getResult() {
         double result =0;
         result=this.get_numberA()+this.get_numberB();
         return result;

     }
 }

　　2.2减法类继承自运算符类:

 package com.lujie;

 public class OperationSub extends Operation{

     public double getResult() {
         double result =0;
         result=this.get_numberA()-this.get_numberB();
         return result;

     }
 }

　　2.3乘法类继承自运算符类:

 package com.lujie;

 public class OperationMul extends Operation{

     public double getResult()  {
         double result =0;
         if(this.get_numberB()==0)
         result=this.get_numberA()*this.get_numberB();
         return result;

     }
 }

　　2.4除法类继承自运算符类:

 package com.lujie;

 public class OperationDiv extends Operation{

     public double getResult()  {
         double result =0;
         try {

             result=this.get_numberA()/this.get_numberB();

         } catch (Exception e) {
             System.out.println("除数不能为0！");
         }

         return result;
     }
 }

3.简单的运算工厂类：

 class OperationFactory{
     public static Operation createOperate(String operate) {

         Operation oper=null;
         switch (operate) {
         case "+":
             oper=new OperationAdd();
             break;
         case "-":
             oper=new OperationSub();
             break;
         case "*":
             oper=new OperationMul();
             break;
         case "/":
             oper=new OperationDiv();
             break;
         }

         return oper;
     }
 }

4.工厂模式举例：

 public static void main(String[] args)  {

         Operation oper;
         oper=OperationFactory.createOperate("/");
         oper.set_numberA(1);
         oper.set_numberB(0);
         double result=oper.getResult();
         System.out.println("结果为："+result);
 }