初学《大话设计模式》——简单工厂模式

一、简单工厂模式:

实质是由一个工厂类根据传入的参数，动态决定应该创建哪一个产品类（这些产品类继承自一个父类或接口）的实例。简单工厂模式的创建目标，所有创建的对象都是充当这个角色的某个具体类的实例。

二、场景

使用Java面向对象语言实现一个计算机控制台程序，要求输入两个数和运算符号，得到结果。
为了使程序达到易扩展，易维护，易复用且灵活的目的，本程序将使用到面向对象编程思想的三大特性：封装、继承和多态，以及简单工厂模式

三、程序代码

程序共有七个类：

MyOperation.java

public class MyOperation {

    private double numberA;
    private double numberB;
    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() throws Exception {
        double result=0;
        return result;
    }
}

OperaAdd.java

public class OperaAdd extends MyOperation {

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

OperaSub.java

public class OperaSub extends MyOperation {

    @Override
    public double getResult() {

        return this.getNumberA()-this.getNumberB();
    }
}

OperaMul.java

public class OperaMul extends MyOperation {

    @Override
    public double getResult() {

        return this.getNumberA()*this.getNumberB();
    }
}

OperaDiv.java

public class OperaDiv extends MyOperation{

    @Override
    public double getResult() throws Exception {
        if(this.getNumberB()==0){
            throw new Exception("除数不能为0");
        }
        return this.getNumberA()/this.getNumberB();
    }
}

OperationFactory.java

public class OperationFactory {

    public static MyOperation createOperation(String operate){
        MyOperation operation=null;
        switch (operate) {
        case "+":
            operation=new OperaAdd();
            break;

        case "-":
            operation=new OperaSub();
            break;

        case "*":
            operation=new OperaMul();
            break;

        case "/":
            operation=new OperaDiv();
            break;
        default:
            operation=new MyOperation();
            break;
        }
        return operation;
    }
}

Calculator.java

import java.util.Scanner;

public class Calculator {

    /**
     * @Title: main
     * @Description: 计算器
     * @param args   
     * @return void    返回类型
     * @throws
     */
    public static void main(String[] args) {
        MyOperation operation=null;
        try {
            System.out.println("请输入数字A:");
            double numberA=Double.valueOf(new Scanner(System.in).nextLine());
            System.out.println("请输入运算符:");
            String operaString=new Scanner(System.in).nextLine();
            System.out.println("请输入数字B:");
            double numberB=Double.valueOf(new Scanner(System.in).nextLine());
            operation=OperationFactory.createOperation(operaString);
            operation.setNumberA(numberA);
            operation.setNumberB(numberB);
            System.out.println("结果是："+operation.getResult());

        } catch (NumberFormatException e) {
            System.out.println("只能输入数字");
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }


    }

}