Why does this code keep looping? ( concept of ActionListener)

Question

I'm a bit lost on this. So here's some code for an ActionListener:

public static void main(String[] args)
  {

    ActionListener listener = new ActionListener(){

      public void actionPerformed(ActionEvent event){
        System.out.println("hello");

      }
    };
    Timer displayTimer = new Timer(5000, listener);
    displayTimer.start();


  }

And it prints hello over and over... I don't quite understand. why doesn't it just print once?

thanks

What do you intend to do? Is ActionListener your custom class? — SSC, Oct 13 '13 at 00:13
@Mr.777 - Nothing, actually , othe than learning about ActionListener and Timer. — Caffeinated, Oct 13 '13 at 00:15
@Adel Well, the code is working as it's written. timer is auto being called after 5 ms and the listener activates which in turn prints hello. That's why it keeps printing after ever 5 ms because you are forcing it to do that. — SSC, Oct 13 '13 at 00:19
@Mr.777 - I think it's getting clearer now. thanks very much! — Caffeinated, Oct 13 '13 at 00:26

score 2 · Accepted Answer · edited May 23 '17 at 11:57

2

Because you are using a Timer and haven't called displayTimer.setRepeats(false);

However, I recommend using a ExecutorService instead of Timer. See this question. There are a few things that a Timer in Java is lacking, see this question which will also help you setup an ExecutorService that will behave just like a Timer that you are used to.

edited May 23 '17 at 11:57

Community

1
1

answered Oct 13 '13 at 00:16

Simon Forsberg

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Agree, unless you want to be sure that the repeated code is called on the Swing event thread. – Hovercraft Full Of Eels Oct 13 '13 at 00:17
3

@HovercraftFullOfEels Even for that, it's possible to call SwingUtilities.invokeLater, isn't it? (Even though *only* calling that might reduce the usefulness of a ExecutorService) – Simon Forsberg Oct 13 '13 at 00:22

score 1 · Answer 2 · answered Oct 13 '13 at 00:15

As the documentation to (Timer)[http://docs.oracle.com/javase/7/docs/api/javax/swing/Timer.html] says, your constructor initializes the timer with both an initial delay and a between-event delay of five seconds. The timer thus executes your ActionListener every five seconds.

Why does this code keep looping? ( concept of ActionListener)

2 Answers2