为什么我的计时器不工作？

Question

public class TimerProgram extends JFrame {
    public TimerProgram(){

       int  DELAY=1000;
       Timer t = new Timer(DELAY,new TimerListener());
          t.start();

    }
      class TimerListener implements ActionListener{
        public void actionPerformed(ActionEvent e) {
            System.out.println("Hello");

          }
        }     

      public static void main(String[]args){
          new TimerProgram();
      }
}

I am trying to make a timer that outputs every second the word hello, but it seems that when I type as the DELAY value 1000 , it outputs hello once and then it terminates. What am I doing wrong ? All help appreciated!

Answer 1

The JVM exited before the Timer fired.

Try:

t.setInitialDelay(0);
t.start();

to see the difference.

Or a better approach is to execute the code on the Event Dispatch Thread (EDT). All GUI code should execute on the EDT. By using SwingUtitities.invokeLater() you ensure the EDT has been created when your code executes:

EventQueue.invokeLater(new Runnable()
{
    public void run()
    {
          new TimerProgram();
    }
});

Read the section from the Swing tutorial on Concurrency for more information about the EDT.