Clear Scanner(in)

Question

on my code, I've a long loop of sequential operation. I make a thread to stop this loop manually. Basically

private static void sendAndCheck() throws InterruptedException {

        stop = false;

        StopChecker r = new StopChecker();
        Thread t = new Thread( r );

        if ( vettore != null ) {
            t.start();
            for ( int i = 0; i < vettore.length; i++ ) {

                do {
                    if ( stop == true ) {
                        break;
                    }

                    //Do something for a lot of time.. (code deleted)

                } while ( !status.equalsIgnoreCase( "PROCESSED" ) ); //<- normal exit 
            }

            //Stop the thread
            stop = true;
        }

    }

and the thread basically is waiting on the standard input for stop character

public class StopChecker implements Runnable {

    public void run() {
        Scanner scanner = new Scanner( System.in );
        System.out.println( "1 - to stop" );
        while ( !Risottometti.stop ) {
            String command = scanner.next();
            if ( command.equalsIgnoreCase( "1" ) ) {
                Risottometti.stop = true;
            }   
            }
        }

    }
}

The problem is that, if the loop exit normally, the thread is locked on the scanner.next, so, the next input is lose inside the still dead thread. How to release the scanner.next from main class? I've tried with scan.close() but doesn't work...

There's another way to stop the loop, without kill the application? i try with keyListener, but i've got a null pointer

Maybe this issue with sincronizity may help you: http://stackoverflow.com/questions/15958228/scannersystem-in-how-to-cancel-skip-input-waiting — Jaime Rey, Aug 26 '15 at 10:36
Looks like a duplicate of http://stackoverflow.com/questions/4983065/how-to-interrupt-java-util-scanner-nextline-call — Simon Kraemer, Aug 26 '15 at 10:37
thanks to @JaimeRey !! I edit the code adding ConsoleInputReadTask and interrupt the thread, and all work fine! Thanks! — Lele, Aug 26 '15 at 11:14
`command.equalsIgnoreCase( "1" )` what is the uppercase version of "1" and what is the lowercase version? :P — Tom, Aug 26 '15 at 11:37
@Tom 1 it's only temporaneous paramether XD after became exit XD XD — Lele, Aug 26 '15 at 12:43

geek-tech · Answer 1 · 2015-08-26T11:29:38.777

0

Have you tried with scan.close() or scanner.close()?

edited Aug 26 '15 at 11:29

answered Aug 26 '15 at 11:03

geek-tech

95
1
9

Yes, I've tryend, but it still waiting. I solve with comment of @jaime Rey – Lele Aug 26 '15 at 11:15
@Lele You shouldn't close that scanner if you intend to read more user input later. – Tom Aug 26 '15 at 11:38

score 0 · Answer 2 · answered Aug 26 '15 at 11:03

This seems to be a case where using Thread.interrupt is a valid occasion. Once the processing is successful, do a stopChecker.interrupt - that should fail the Scanner.next with a ClosedByInterruptException exception. Note that according to javadoc System.in might be closed because of this operation.

If that is not an option, the only solution is to not to use Scanner and do your option read in a non-blocking way.

score 0 · Answer 3 · answered Aug 26 '15 at 11:31

0

Please change the code as follows.

1) Replace while loop with do - while block

2) Change Scanner code as follows

 do{
    while ( scanner.hasNext() ) {
         String command = scanner.nextLine();
         System.out.println("line:"+command);
    }
 } while ( conditionFlag)

When the condition is false, call

scanner.close();

answered Aug 26 '15 at 11:31

Ravindra babu

42,401
8
208
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`scanner.hasNext()` is always true of the scanner reads from `System.in` and that stream isn't closed. – Tom Aug 26 '15 at 11:37
But I am closing the stream outside of while loop once the thread has been stopped – Ravindra babu Aug 26 '15 at 11:46
1

"once the thread has be stopped" and when should that happen if the thread stays in the `while` lopp? And since you're closing the scanner you also make it impossible to read more user data later. – Tom Aug 26 '15 at 11:50

Clear Scanner(in)

3 Answers3