public interface Operation {
    //提供计算两个数字的方法
    double getResult(double num1,double num2);

}

public class Addition implements Operation { //加法

    @Override
    public double getResult(double num1, double num2) {
        return num1+num2;
    }

}

public class Minus implements Operation { //减法

    @Override
    public double getResult(double num1, double num2) {
        return num1-num2;
    }

}

public class Multiplication implements Operation {//乘法

    @Override
    public double getResult(double num1, double num2) {
        return num1*num2;
    }

}

public class Division implements Operation {//除法

    @Override
    public double getResult(double num1, double num2) {
        return num1/num2;
    }
}

public class OperationFactory {  //计算机的工厂类
    /*
     * 工厂模式 是我们最常用的实例化对象的模式！
     * 用工厂的方法替代new！
     * 虽然代码量没有减少  但是 提高了程序的扩展性！
     */
    public static  Operation  getOperation(String o){
        Operation operation=null; //多态
        switch (o) {
        case "+":
            operation=new Addition();
            break;
        case "-":
            operation=new Minus();
            break;
        case "*":
            operation=new Multiplication();
            break;
        case "/":
            operation=new Division();
            break;
        }
        return  operation;
    }
}

public class FactoryTest {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        System.out.println("请输入第一个数字：");
        double num1 = scanner.nextInt();
        System.out.println("请输入运算符：");
        String operation = scanner.next();
        System.out.println("请输入第二个数字：");
        double num2 = scanner.nextInt();
        //创建运算的实例对象
        Operation o = OperationFactory.getOperation(operation);
        //输出结果
        System.out.println(o.getResult(num1, num2));
    }
}