为什么两次输入相同的数字会导致我的程序失败？

Question

I am just starting out learning Java and I am in the process of working through a much more efficient program to solve this problem, but I would like to understand why entering the same number twice causes the program to not run all the way through?

I need to write a program where the user enters three numbers and they get sorted in non-descending order.

import java.util.Scanner;

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

java.util.Scanner input = new java.util.Scanner(System.in);

int num1;
int num2;
int num3;

System.out.println("Please enter three (3) numbers");
num1 = input.nextInt();
num2 = input.nextInt();
num3 = input.nextInt();

System.out.println("Thanks. You entered " + num1 + ", " + num2 + ", " +    num3 + ".");

if (num1 > num2 && num1 > num3){
    if (num2 > num3 || num2 == num3){
        System.out.println("Your numbers in non-descending order are "  + num3 + ", " + num2 + ", " + num1 + ".");
    }
    else if (num3 > num2 || num3 == num2){
        System.out.println("Your numbers in non-descending order are " + num2 + ", " + num3 + ", " + num1 + ".");
    }
}
else if (num2 > num1 && num2 > num3){
    if (num1 > num3 || num1 == num3){
        System.out.println("Your numbers in non-descending order are "  + num3 + ", " + num1 + ", " + num2 + ".");
    }
    else if (num3 > num1 || num3 == num1){
        System.out.println("Your numbers in non-descending order are " + num1 + ", " + num3 + ", " + num2 + ".");


                }   
            }
else if (num3 > num1 && num3 > num2){
    if (num1 > num2 || num1 == num2){
        System.out.println("Your numbers in non-descending order are " + num2 + ", " + num1 + ", " + num3 + ".");
    }
    else if (num2 > num1 || num2 == num1){
        System.out.println("Your numbers in non-descending order are " + num1 + ", " + num2 + ", " + num3 + ".");

        }
      }
     }
   }

Answer 1

You have to clean the buffer, try to place a scanner.nextLine(); after each nextInt() . This method returns the rest of the current line, excluding any line separator at the end. The position is set to the beginning of the next line. Since this method continues to search through the input looking for a line separator, it may buffer all of the input searching for the line to skip if no line separators are present.

Answer 2

You can't directly take three ints without clearing the buffer in some way. This is a friendly way i like to do it

System.out.println("Please enter number one :: ");
num1 = input.nextInt();
System.out.println("Please enter number two :: ");
num2 = input.nextInt();
System.out.println("Please enter number three :: ");
num3 = input.nextInt(); 

This will give you the results you expected.

Another flaw in your program is the logic in determining which number is the smallest. You should have something similar to this :

if(num1 >= num2 && num1 >= num3){
    if(num2 >= num3)
        System.out.println(num3 +" "+ num2 + " "+ num1);
    else
        System.out.println(num2+" "+num3+" "+num1);
}else if(num2 >= num1 && num2 >= num3){
    if(num1 >= num3)
        System.out.println(num3 +" "+ num1 + " "+ num2);
    else
        System.out.println(num1 +" "+ num3 + " "+ num1);
}else{
    if(num1 >= num2)
        System.out.println(num2 +" "+ num1 + " "+ num3);
    else
        System.out.println(num2 +" "+ num1 + " "+ num3);
}

So putting this all together will allow you to take your three int inputs correctly, then sort and display them in descending order.