Trouble using two Scanners for different input

Question

When using Scanner to read from standard input, the newline one enters apart from what's intended to be read is not consumed, causing trouble with subsequent inputs. This can be fixed using something like exampleScanner.nextLine(). However I'm trying to use two different scanners as below and am not able to fix the problem. I know there are a ton of questions and answers related to this type of problem with Scanner but I still can't seem to find an answer to my particular problem. Is my problem fixable or do I have to make do with one Scanner? Here's some code:

import java.util.Scanner;
import java.util.NoSuchElementException;

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

    char sym = ' ';
    int x = 0;

    /* scan for char (string) */
    Scanner scanForSym = new Scanner(System.in);
    System.out.print("Enter a symbol: ");
    try {
      sym = scanForSym.next().charAt(0);
    } catch (NoSuchElementException e) {
      System.err.println("Failed to read sym: "+e.getMessage());
    }
    scanForSym.nextLine(); // makes no diff when using different Scanner
    scanForSym.close();

    /* scan for int with different scanner */
    Scanner scanForX = new Scanner(System.in);
    System.out.print("\nEnter an integer: ");
    try {
      x = scanForX.nextInt();
      //x = scanForSym.next(); // this works fine (comment out the close above)
    } catch (NoSuchElementException e) {
      System.err.println("Failed to read x: "+e.getMessage());
    }
    scanForX.close();

    System.out.println("sym: "+sym);
    System.out.println("x: "+x);
  }
}

Try `nextLine()` instead of `next()`. The same Scanner can be used to get the int. — Andrew S, Sep 19 '17 at 18:26
I'm aware of that, as I indicated. The question is whether the above can be resolved using two scanners, not if the above could be done with a single scanner. — Erik Vesterlund, Sep 19 '17 at 18:56

score 1 · Answer 1 · answered Sep 19 '17 at 19:13

Error is associated with this line:

scanForSym.close();

which closes the System.in InputStream. So then this call

x = scanForX.nextInt();

throws an IOException since scanForX is trying to read from an already closed InputStream.

Try moving

scanForSym.close();

somewhere below

x = scanForX.nextInt();

Although (restating from the comments) it's not clear why you want to use multiple Scanner instances when they're both associated with System.in.

Trouble using two Scanners for different input

1 Answers1