java - 我的 'else' 语句有什么问题？

Question

运行程序时，出现以下错误:

输入一个数字: 5 你原来的号码是5.0 错误输入的不是数字。

我尝试了所有我能想到的方法，但我被难住了。以下是代码片段，

import java.util.Scanner;

public class NegativeNumberConversion {

    public static void main(String[] args) {
        // Convert negative numbers to positive and display back to user

        // Create a console object for Scanner class
        Scanner input = new Scanner (System.in);

        // Declare variable
        double numberOne = 0;

        // Prompt user to enter number
        System.out.println("Enter a number: ");

        // Read in the number
        numberOne = input.nextDouble();

        // If the number is positive - display it
        if (numberOne > 0){

        // Display it - Explain that it is the original number
        System.out.println("Your original number is " + numberOne);

        }else  {

        // Report the error
        System.out.println("***ERROR*** The input is not a number.");

        // Terminate the error
        System.exit(1);

    }

        // If the number negative - convert it to positive - 
        if(numberOne < 0){


        // Display it - Explain that it was converted
        System.out.println("Your number was converted to " + (-1*numberOne) + " because it was negative.");

        }else{
        // Report the error
        System.out.println("***ERROR*** The input is not a number.");

        // Terminate the error
        System.exit(1);
    }

        // Close input
        input.close();
    }
}

Answer 1

问题在于 if 语句的设置方式

要解决此问题，请将第二种情况包含在 else if 中。

if (numberOne > 0) {
    System.out.println("Your original number is " + numberOne);
}
else if (numberOne < 0) {
    System.out.println("Your number was converted to " + (-1 * numberOne) + " because it was negative.");
}
else {
    // Report the error
    System.out.println("***ERROR*** The input is not a number.");
    // Terminate the error
    System.exit(1);
}

编辑:帮助您理解为什么它不起作用(而不是仅仅显示解决方案)。当有人输入一个输入时，无论它是正数还是负数，两个 if 语句都会进行比较，并且由于数字不能同时存在，因此始终会运行 else 语句之一。