Java 计算器切换问题

Question

我结合了我在这里看到的几种不同的方法。有谁知道如何解决我遇到的这个问题？当您使用此代码时，它要求您输入数学运算符，但是当我输入 +9 或 -% 时，它仍然可以工作并使用第一个符号。如果有人输入 */ 而不是 *.我什至尝试将 case 切换为数字（即 case 1:)，如果我将加法设置为 1，它会做同样的事情，如果我输入 15，它会读取一个并做加法。有什么想法吗？

import java.util.Scanner;

public class javacalculator {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        Scanner operation = new Scanner(System.in);

        double num1, num2, answer;
        char userOperation;
    

        System.out.print("Enter your full name: ");
        String userName = input.nextLine();

        System.out.println("+ Addition");
        System.out.println("- Subtraction");
        System.out.println("* Multiplication");
        System.out.println("/ Division");
        System.out.println("% Modulus");
        System.out.println("\n");


        System.out.print("Enter mathematical operator e.g. + for Addition: ");
        userOperation = operation.next().charAt(0);

        boolean invalidOperator = false;

        switch (userOperation) {
        case '+':
            System.out.print("Enter first number: ");
            num1 = input.nextInt();

            System.out.print("Enter the second number: ");
            num2 = input.nextInt();

            answer = num1 + num2;

            System.out.print(num1 + " + " + num2 + " = " + answer);


            break;
        case '-':
            System.out.print("Enter first number: ");
            num1 = input.nextInt();

            System.out.print("Enter the second number: ");
            num2 = input.nextInt();

            answer = num1 - num2;

            System.out.print(num1 + " - " + num2 + " = " + answer);

            break;
        case '*':
            System.out.print("Enter first number: ");
            num1 = input.nextInt();

            System.out.print("Enter the second number: ");
            num2 = input.nextInt();

            answer = num1 * num2;

            System.out.print(num1 + " * " + num2 + " = " + answer);


            break;
        case '/':
            System.out.print("Enter first number: ");
            num1 = input.nextInt();

            System.out.print("Enter the second number: ");
            num2 = input.nextInt();

            answer = num1 / num2;

            System.out.print(num1 + " / " + num2 + " = " + answer);


            break;

        case '%':
            System.out.print("Enter first number: ");
            num1 = input.nextInt();

            System.out.print("Enter the second number: ");
            num2 = input.nextInt();

            answer = num1 % num2;

            System.out.print(num1 + " % " + num2 + " = " + answer);


            break;
        default:
            System.out.println("Invalid operator!");
            break;
    }


}

}

Answer 1

让我们分解一下：operation.next().charAt(0);

operation.next() -> 给你完整的输入字符串

.charAt(0); -> 返回完整输入字符串的第一个字符

所以我们输入 +9 或 */ -> 它返回第一个元素。

现在让我们处理这个案例：

String o = operation.next(); // here is complete input
if(o.length()!=1){
userOperation = 0;     //if length of input is not 1 we set custom value
}else{
userOperation = o.charAt(0); //get and set the first and only element 
}

希望对您有所帮助！