设计模式之简单工厂模式

　　　　今天学习了简单工厂模式，总结一下。

　　　　简单工厂模式的核心思想是：由一个工厂实体决定创建出哪一种产品的实例。

　　　　比较简单，因此直接上代码：

    这个例子我们实现一个简单的计算器。我们先定义一个计算行为接口，行为比较简单就是计算。

package com.java.simpleFactory;

public interface CalcOperation {
    public float doCalc();
}

接着我们分别用加减乘除不同的运算去实现这个接口。

package com.java.simpleFactory;

public class AddOperation extends DefaultOperation implements CalcOperation{
    
    public AddOperation(float a,float b){
        this.setA(a);
        this.setB(b);
    }
    
    @Override
    public float doCalc() {
        return this.getA()+this.getB();
    }

}


package com.java.simpleFactory;

public class MinusOperation extends DefaultOperation implements CalcOperation {
    
    public MinusOperation(float a,float b) {
        this.setA(a);
        this.setB(b);
    }
    
    
    @Override
    public float doCalc() {
        return this.getA()-this.getB();
    }

}

package com.java.simpleFactory;

public class MultOperation extends DefaultOperation implements CalcOperation {

    public MultOperation(float a,float b) {
        this.setA(a);
        this.setB(b);
    }

    @Override
    public float doCalc() {
        return this.getA()*this.getB();
    }

}

package com.java.simpleFactory;

public class DvdOperation extends DefaultOperation implements CalcOperation {

    public DvdOperation(float a,float b) {
        this.setA(a);
        this.setB(b);
    }

    @Override
    public float doCalc() {
        if(this.getB()==0)
            return 0;
        return this.getA()/this.getB();
    }

}

最后就是我们的工厂类了

package com.java.simpleFactory;

public class OperationFactory {

    public CalcOperation CreateOpreation(String sign,float a,float b){
        CalcOperation calcOperation = null;
        switch(sign){
            case "+":
                calcOperation = new AddOperation(a, b);
                break;
            case "-":
                calcOperation = new MinusOperation(a, b);
                break;
            case "*":
                calcOperation = new MultOperation(a, b);
                break;
            case "/":
                calcOperation = new DvdOperation(a, b);
                break;
        }
        return calcOperation;
    }

}

测试一下

package com.java.simpleFactory;

public class Test {

    public static void main(String[] args) {
        OperationFactory factory=new OperationFactory();
        CalcOperation operation = factory.CreateOpreation("/", 2, 3);
        System.out.println(operation.doCalc());

    }

}

简单工厂模式看着很简单，但是作用很大。推荐大佬的一片文章：http://www.cnblogs.com/zuoxiaolong/p/pattern4.html