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);
}