InvokeLater() and invokeAndWait()

Question

I'm somewhat confused about when to use these.
from http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html - it says "you must take extreme care that Swing components and models are created, modified, and queried only from the event-dispatching thread"
I also understand that these two methods are basically the same though invokeAndWait only returns once the run() has completed while invokeLater will return immediately.
So, when should I use these? and which one should I use?
If I'm creating the GUI initially, use the invokeAndWait()
If I'm updating/quering the GUI components, use invokeLater()
is this the correct way of thinking?

Answer 1

You only need to use these methods if you are updating your GUI from a Thread you have spawned. These methods insure the GUI udpate is performed from the event dispatcher thread as those methods put the GUI update in the event queue.
If you are already updating the GUI from the event dispatcher thread (i.e. from an ActionListener, MouseListener, etc) you don't need to use them.
For instance lets say you do an expensive database query (takes a noticeable amount of time to return results) when you press a button. If you just do the database query in the main thread the rest of your application will block while the db query is performed. So you would spawn a new thread with your db query in it. However, now lets say when the db query is over you want to update some status label to notify the user. You would put the label update in a Runnable object and pass that to invokeLater() which would put your runnable oject in the event queue which would eventually get executed by the event dispatcher thread.
Now the rest of your application is responsive while the db query is occuring. And the label will be updated in a thread safe way when the db query is done.
Generally invokeLater() is used, as invokeAndWait() blocks until the runnable object you add to the event queue is executed. This isn't generally desireable. More or less you can safely ignore invokeAndWait(), although keep it in mind for those rare occasions where its usage would be desireable.
Here a very generic example:
public void actionPerformed(ActionEvent e) {
      //Button has been pressed lets query the db in a thread
      new Thread() {
            public void run() {
                //Hit the DB
                Runnable changeLabel = new Runnable() {
                    public void run() {
                        label.setText("tell user db query is done");
                //Put the changing of the label in the event queue
                EventQueue.invokeLater(changeLabel);
        }.start();
}