Java: while loop for user input not executing

Question

Edit: the problem turned out to be caused by my closing System.in in a previous part of the program, thereby making it unusable later on.

I'm trying to create a loop for user input but it's not functional...

Here's what I've got:

    Scanner userkey = new Scanner(System.in);

    System.out.println("Enter commands");
    while(userkey.hasNext()){

        if (userkey.next().equals("exit")){
            System.out.println("EXIT!!!!");
            break;
        }
        System.out.println("In while loop test");
    }

I guess userkey.hasNext() is return false for some reason...

Don't add a semicolon after your `if` statement. Is there any other error? — Stéphane Bruckert, Jun 09 '14 at 21:37
@StéphaneBruckert I think in that case it'd just be compiled to an empty statement — awksp, Jun 09 '14 at 21:38
@StéphaneBruckert Edited my post. That wasn't in my code I'm testing. Still having the problem. — TryingToCode, Jun 09 '14 at 21:39
It works fine for me. You don't print anything to the console asking the user for anything, so it's likely nothing's been entered. — Ryan J, Jun 09 '14 at 21:43
@SotiriosDelimanolis No, it's not accepting input. The code simply ends. I'm trying to continiously accept user input via that while loop. Obviously my code is lacking... — TryingToCode, Jun 09 '14 at 21:45
@merlin2011 I don't get the chance to type anything in. I just see "Enter commands" followed by build successful (netbeans) — TryingToCode, Jun 09 '14 at 21:48
Your code isn't lacking, something else is going on... I've tested using an IDE as well as the command line. No difference. — Ryan J, Jun 09 '14 at 21:48
@RyanJ How do you test this using IDE. Where do you enter the text? — Nu2Overflow, Jun 09 '14 at 21:50
I use IntelliJ IDEA, which has a console built in. I can type directly into that. — Ryan J, Jun 09 '14 at 21:50
@RyanJ Ok thanks. Maybe I've got a conflict with Scanner being open or something in another part of the program. — TryingToCode, Jun 09 '14 at 21:50
Ok it turns out my problem was that I was closing System.in in an earlier part of the code, making it unusable here. [I found this post, which encounters my same problem](http://stackoverflow.com/questions/21710168/issue-with-java-scanner-not-taking-nextline-on-new-instance) — TryingToCode, Jun 09 '14 at 22:00

score 0 · Answer 1 · answered Jun 09 '14 at 21:50

try this:

import java.util.Scanner;

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

         Scanner scanner = new Scanner(System.in);
            String readString = scanner.nextLine();
            while(readString!=null)
            {
                System.out.println(readString);
                if(readString.equals(""))
                    System.out.println("Read Enter Key.");
                if(scanner.hasNextLine())
                    readString = scanner.nextLine();
                else
                    readString = null;

                if(readString.equals("exit")){
                    System.out.println("EXIT");
                    break;
                }
            }

    }

}

Even your code should work, but this is a more verbose version.

score 0 · Answer 2 · answered Jun 09 '14 at 22:20

Try this code:

import java.util.Scanner;
    public static void main(String[] args) {
        // TODO code application logic here
        Scanner userkey = new Scanner(System.in);
        System.out.println("Enter commands");
        do  {
            if (userkey.next().equals("exit")) {
                System.out.println("EXIT!!!!");
                break;
            }
            System.out.println("In while loop test");
        }while(userkey.hasNext());

    }
}

Java: while loop for user input not executing

2 Answers2