Question

I’m trying to update the tab being displayed, however it seems to wait until the end of the method and then update. Is there a way to make the tab being displayed update immediately?

Here is an example of the code where I’m having this issue:

private static void someButtonMethod() 
{
    Button = new JButton("My Button");
    Button(new ActionListener() {
        public void actionPerformed(ActionEvent e) 
        {
            tabs.setSelectedIndex(1);

            // Do some other things (In my case run a program that takes several seconds to run).
            runProgram();
        }
    });
}

Answer 1

The reason for this is that the method is being executed in the Event Dispatch thread, and any repaint operations will also occur in this thread. One “solution” is to update the tab index and then schedule the remaining work to be invoked later on the EDT; this should cause the tab state to be updated immediately; e.g.

public void actionPerformed(ActionEvent evt) {
  tab.setSelectedIndex(1);

  SwingUtilities.invokeLater(new Runnable() {
    public void run() {
      // Do remaining work.
    }
  });
}

EDIT

Per your comment below an example of how to invoke a SwingWorker in order to call your runProgram method would look something like this:

// Typed using Void because runProgram() has no return value.
new SwingWorker<Void, Void>() {
  protectedVoid doInBackground() {
    runProgram();
    return null; // runProgram() doesn't return anything so return null.
  }

  protected void done() {
    // Called on the EDT when the background computation has completed.
    // Could insert code to update UI here.
  }  
}.execute()

However, I sense a bigger problem here: The fact that you are seeing a significant delay in updating the tab makes me think you are performing long running calculations on the EDT. If this is the case you should consider performing this work on a background thread. Take a look at the SwingWorker class.