My function with scanner crashes instead of returning input number (java)

Question

I created a function that asks user for a number. The function checks if it is a positive integer and if it is an integer at all, and should return that number.

The program crashes every time if the user puts in a positive integer. I am new to eclipse IDE and don't know where to look for a log of runtime errors.

I already tried return height.nextInt() and deleted the z variable, didn't work. (This function is for a bigger program that eventually prints out a pyramid.)

package skener;

import java.util.Scanner;

public class MyClass 
{
    public static int z = 0;
    public static int userInput()
    {
        Scanner height = new Scanner(System.in);
        System.out.println("Please choose a number: ");
        while(!height.hasNextInt() || (height.nextInt() < 0))
        {
            //height = new Scanner(System.in);
            System.out.println("Wrong number, try again: ");
            height = new Scanner(System.in);

        }
        z = height.nextInt();
        height.close();
        return z;

    }
    public static void main(String[] args)
    {
        System.out.println(userInput());
    }
}

If user input is 3, I expect to get return 3, to use in another program. Instead the program simply terminates and the terminal doesn't provide any error messages and doesn't return the input.

Answer 1

your program should be like below,

Scanner height = new Scanner(System.in);
        System.out.println("Please choose a number: ");
        z = height.nextInt();
        while((z < 0))
        {
            System.out.println("Wrong number, try again: ");
            z = height.nextInt();

        }

        return z;

here we are getting the integer value in z and we are checking the condition and returning if it's positive or we will ask user to enter again. Please use import scanner module in import java.util.Scanner;

Answer 2

I believe this is what you want.

      Scanner height = new Scanner(System.in);

      System.out.println("Please choose a number: ");
      int z = -1; // default value means no valid integer entered.
      // ensure that the next value is an int and if so. 
      // it is >= 0.

      while (height.hasNextInt() && (z = height.nextInt()) < 0) {
         System.out.println("Wrong number, try again: ");
      }
      // Display the value
      System.out.println("z = " + z);
      // and if in a method, return it.
      return z;

Your solution was very close. You should not have closed the scanner because that also closes the Console input which you would not be able to re-open and read from.

And as you specified in your original code, if you don't check for a non-numeric value, before getting an int, your code will throw an exception.