java - 当用户输入非 double 值时如何打印错误消息？

Question

我正在尝试创建一个Java程序，从用户那里读取 double 值，打印这两个数字之间的差值，以便差值始终为正。如果输入数字以外的任何内容，我需要显示错误消息。请帮忙，谢谢!!

当我运行程序并输入第二个 double 值时，没有任何反应。我也尝试添加 try 和 catch 但出现错误，指出 num1 无法解析为变量:(

import java.util.Scanner;
public class Positive {

    public static void main(String[] args) {

        //Reads input
        Scanner sc = new Scanner(System.in);  

        System.out.println ("Please enter a double vaule: ");

            double num1 = Math.abs(sc.nextDouble());
            System.out.println("Please enter a second double vaule: " );
            double num2 = Math.abs(sc.nextDouble());
            double total  = 0;
            double total2 = 0;      

        if (sc.hasNextDouble()) {
        num1 = sc.nextDouble();

        if (num1>num2) {
            total = ((num1 - num2)); 
            System.out.println("The difference is " + total);
        }   

        if ((num1 < num2)); {
            total2 = ((num2 - num1));
            System.out.println("The difference is "+ total2);
        }

        }else {
            System.out.println("Wrong vaule entered");
        }

    }
}

Answer 1

你的想法是对的。您只需删除最后一个 if 后面的分号 (;) 并正确嵌套您的条件:

if (sc.hasNextDouble()) {
    num1 = sc.nextDouble();

    if (num1 > num2) {
        total = (num1 - num2); 
        System.out.println("The difference is " + total);
    }   
    else if (num1 < num2) {
        total2 = (num2 - num1);
        System.out.println("The difference is "+ total2);
    }
} else {
    System.out.println("Wrong vaule entered");
}