一、概述

       简单工厂模式又称静态工厂模式。属于创建型模式，但不属于23中GOF设计模式之一。

       简单工厂模式，即通过专门定义一个工厂类来负责创建其他类的实例，被创建的实例通常都具有共同的父类。 

二、编程实现

       该程序主要通过模拟计算器的功能实现。

1、创建共同父类

public class Operation {
    private int numberA;
    private int numberB;

    public int getNumberA() {
        return numberA;
    }

    public void setNumberA(int numberA) {
        this.numberA = numberA;
    }

    public int getNumberB() {
        return numberB;
    }

    public void setNumberB(int numberB) {
        this.numberB = numberB;
    }
    public int getResult(){
        int result = 0;
        return result;
    }
}

2、创建基于父类的子类

     2.1 加法类

public class OperationAdd extends Operation {

    @Override
    public int getResult() {
        int result = 0;
        result = super.getNumberA() +super.getNumberB();
        return result;
    }
}

 2.2 减法类

public class OperationSub extends Operation {

    @Override
    public int getResult() {
        int result = 0;
        result = super.getNumberA() - super.getNumberB();
        return result;
    }
}

2.3 乘法类

public class OperationMult extends Operation {

    @Override
    public int getResult() {
        int result = 0;
        result = super.getNumberA() * super.getNumberB();
        return result;
    }
}

2.4 除法类

public class OperationDiv extends Operation {

    @Override
    public int getResult() {
        int result = 0;
        try {
            result = super.getNumberA() / super.getNumberB();
        }catch (Exception e){
            System.out.println("除数不能为0.");
        }
        return result;
    }
}

3、创建工厂类

public class OperationFactory {

    public static Operation createOperate(String operateType){
        Operation operation = null;
        switch (operateType){
            case "+":
                operation = new OperationAdd();
                break;
            case "-":
                operation = new OperationSub();
                break;
            case "*":
                operation = new OperationMult();
                break;
            case "/":
                operation = new OperationDiv();
                break;
        }
        return operation;
    }
}

4、测试

public class Test {
    public static void main(String[] args) {
        Operation oper = OperationFactory.createOperate("+");
        oper.setNumberA(50);
        oper.setNumberB(10);
        System.out.println(oper.getResult());
    }
}

注：参考文献《大话设计模式》程杰著。