Question

How can I call a method every n seconds?

I want to do a slideshow with Swing and CardLayout and every n seconds
it must show a different image calling a different method

Answer 1

import java.util.*;

class MyTimer extends TimerTask
{
  public void run()
  {
    //change image
  }
}

then in your main you can schedule the task:

Timer t = new Timer();
t.schedule(new MyTimer(), 0, 5000);

first number is initial delay, second is the time between calls to run() of your TimerTask: 5000 is 5 seconds.

As BalusC noted usually you dispatch swing changes on AWT event thread. In this simple cause it shouldn’t create problems when changing background from an outside thread, in any case you should use

public static void SwingUtilities.invokeLater(Runnable whatToExecute)

to dispatch your change on the right thread.

If you prefer BalusC approach just use an ActionListener:

public void BackgroundChange implements ActionListener
{
  public void actionPerformed(ActionEvent e)
  {
    //change bg
  }
}

javax.swing.Timer t = new javax.swing.Timer(5000, new BackgroundChange());

They both provide same functionality, but this later one is already prepared to work out together with Swing threads mantaining compatibility and avoiding strange synchronizations issues.