设计模式五：策略模式

定义算法家族

abstract class OperateStrategy {

    public abstract double operate(double num1,double num2) throws Exception;
}

加法

public class OperateAdd extends OperateStrategy {
    @Override
    public double operate(double num1, double num2) {
        return num1 + num2;
    }
}

减法

public class OperateSub extends OperateStrategy {
    @Override
    public double operate(double num1, double num2) {
        return num1 - num2;
    }
}

乘法

public class OperateMul extends OperateStrategy {
    @Override
    public double operate(double num1, double num2) {
        return num1 * num2;
    }
}

除法

public class OperateDiv extends OperateStrategy {
    @Override
    public double operate(double num1, double num2) throws Exception {
        if (num2 == 0) {
            throw new Exception("被除数不能为0！");
        }
        return num1 / num2;
    }
}

判断使用哪个算法

public class OperatorContextStrategy {

    OperateStrategy operateStrategy = null;

    public OperatorContextStrategy(String type) {
        switch (type) {
            case "+":
                operateStrategy = new OperateAdd();
                break;
            case "-":
                operateStrategy = new OperateSub();
                break;
            case "*":
                operateStrategy = new OperateMul();
                break;
            case "/":
                operateStrategy = new OperateDiv();
            default:
                break;
        }
    }

    public double getResult(double num1, double num2) throws Exception{
        return operateStrategy.operate(num1, num2);
    }
}

测试类：

public class Test {
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入第一个数值：");
        double numOne = Integer.parseInt(scanner.nextLine());
        System.out.println("请输入第二个数值：");
        double numTwo = Integer.parseInt(scanner.nextLine());
        System.out.println("请输入操作符（+、-、*、/）：");
        String oper = scanner.nextLine();
        double result = 0;

        OperatorContextStrategy operator = new OperatorContextStrategy(oper);
        try {
            result = operator.getResult(numOne, numTwo);
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println(result);

    }
}