Java计算器错误的运算符提示

我有一个计算器类，我希望操作输入特定于这些字符串“+，-，/，*”，如果不是，我希望打印一条消息以再次输入运算符。 如果有人想减少我的代码，请做吧。谢谢

这是我的密码

import java.util.Scanner;

公共类计算器1{

public static void main(String[] args) {    
    Scanner num = new Scanner(System.in);
    String operation;
    Double fnum, lnum, answer;
    System.out.println("Enter first Number: ");
    while (!num.hasNextDouble())
    {
        num.next();
        System.out.print("Enter first Number: ");
    }
    fnum = num.nextDouble();
    System.out.println("Enter Operation: ");
    //HERE IM BEING CONFUSED
    while (!num.equals("+, -, /, *"))
    {
        num.next();
        System.out.print("Enter Operator: ");
    }
    operation = num.next();
    //End
    System.out.println("Enter Second Number: ");
    while (!num.hasNextDouble())
    {
        num.next();
        System.out.print("Enter Second Number: ");
    }
    lnum = num.nextDouble();




    switch (operation) {
    case "+":
        answer = fnum + lnum;
        System.out.print("Equals= " + answer);
        break;
    case "-":
        answer = fnum - lnum;
        System.out.print("Equals= " + answer);
        break;
    case "*":
        answer = fnum * lnum;
        System.out.println("Equals= " + answer);
        break;
    case "/":
        answer = fnum / lnum;
        System.out.println("Equals= " + answer);
        break;
    default:
        System.out.println("wrong operator");
        break;


    }
}

---

}这是一种将运算符与开关语句一起使用的方法

public static void main(String[] args) {

    Scanner num = new Scanner(System.in);
    double v1,v2;
    String v3;

    System.out.print("Enter first number: ");
    v1 = num.nextDouble();
    System.out.print("Enter second number: ");
    v2 = num.nextDouble();
    System.out.print("Enter operation [+]   [-]   [*]   [/]: ");
    v3 = num.next();

    System.out.println( ("+".equals(v3) ) ? Operators.ADD.calculate(v1, v2) : "....");

    }

public enum Operators {
    ADD;

    double calculate(double x, double y) {
        switch (this) {
            case ADD:
                return x + y;
            default:
                throw new AssertionError("Unknown operations " + this);
        }
    }

}

---

！num.equals（“+，-，/，*”）

您的问题是什么？调试并逐步完成代码时会发生什么？什么是错误？

num

是一个

扫描仪

。它永远不会等于

字符串。