简单工厂模式-实现简易计算器

今天遇到一个面试题，题目为“C++、Java、或VB.NET任意一种面向对象语言实现一个计算器控制台程序，要求输入两个数和运算符号，得到结果”。

通常面对这样的问题，会心有成竹、下笔有神，心想写一个简易的计算机控制程序还不简单吗？不就是输入数字，在输入符号，最后得出结果。但是这个题目真的只是考验这个逻辑吗？所有的编程初学者都会有这样的问题，就是碰到问题就直觉地用计算机能够理解的逻辑来描述和表达待解决的问题及具体的求解过程。这其实是用计算机的方式去思考，比如计算器这个程序，先要求输入两个数和符号，然后根据运算符号判断选择如何运算，得到结果，这个本身没有错误，但是这样的思维却使我们的程序只为满足实现当前的需求，程序不容易维护，不容易扩展，更不容易复用。从而达不到高质量代码的要求。为了达到可维护、可扩展、可复用的目的我们选用简单工厂模式。

运算类中包含两个数字及一个方法。

package com.qqkj.design.demo1.entity;


public class Operation {

    private double numberA = 0;

    private double numberB = 0;

    public double getNumberA() {
        return numberA;
    }

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

    public double getNumberB() {
        return numberB;
    }

    public void setNumberB(double numberB) {
        this.numberB = numberB;
    }

    public double getResult(){
        double result = 0;
        return result;
    }
}

package com.qqkj.design.demo1.entity;


public class OperationAdd extends Operation{

    @Override
    public double getResult() {
        double numberA = super.getNumberA();
        double numberB = super.getNumberB();
        return numberA + numberB;
    }
}

package com.qqkj.design.demo1.entity;


public class OperationSub extends Operation{
    @Override
    public double getResult() {
        double numberA = super.getNumberA();
        double numberB = super.getNumberB();
        return numberA - numberB;
    }
}

package com.qqkj.design.demo1.entity;


public class OperationMul extends Operation{
    @Override
    public double getResult() {
        return super.getNumberA()*super.getNumberB();
    }
}

package com.qqkj.design.demo1.entity;


public class OperationDiv extends Operation{
    @Override
    public double getResult() {
        double result = 0;
        double numberA = super.getNumberA();
        double numberB = super.getNumberB();
        if(numberB == 0){
            throw new RuntimeException("除数不能为0");
        }else {
            result = numberA / numberB;
        }
        return result;
    }
}

package com.qqkj.design.demo1.entity;


public class OperationFactory {

    public static Operation createOperation(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;
    }
}

package com.qqkj.design.demo1.controller;

import com.qqkj.design.demo1.entity.Operation;
import com.qqkj.design.demo1.entity.OperationFactory;

public class OperationTest {
    public static void main(String[] args) {
        Operation operation = OperationFactory.createOperation("+");
        operation.setNumberA(10);
        operation.setNumberB(11);
        double result = operation.getResult();
        System.out.println("结果为："+result);
    }
}

还没想好。。。。。。。