CODEWITHSUNDEEP
javamultithreadingswingawtevent-dispatch-thread
MC Emperor
MC Emperor

Reputation: 23027

Why is the painting of a component delayed?

I want to paint a panel blue, then wait five seconds, then do other stuff.
Now I have the following piece of code, which I expect to do what I want. Here it is:

JPanel somePanel = getSomePanel();
somePanel.setBackground(Color.BLUE);
Object lock = new Object();
synchronized (lock) {
    try {
        lock.wait(5000);
    }
    catch (InterruptedException exc) { }
}
// Do other stuff

But instead, it waits five seconds and then paints the component blue.

Upvotes: 0

Views: 89

Answers (3)

lbalazscs
lbalazscs

Reputation: 17794

The others are right, if you are waiting on the event dispatch thread, then this thread will not do any painting in the meantime.

There is a trick however, that should help you without starting a new thread: call paintImmediately after setting the background color.

somePanel.paintImmediately(0, 0, somePanel.getWidth(), somePanel.getHeight());

Upvotes: 3

Hovercraft Full Of Eels
Hovercraft Full Of Eels

Reputation: 285405

Don't do the synchronized code with locking on the Swing event thread as all you're doing is locking Swing itself and freezing the GUI. Google "Concurrency in Swing" for the details. Myself I'd use a Swing Timer for this. Note that your post uses the tag, but you don't actually do multithreading anywhere.

Upvotes: 4

Martin James
Martin James

Reputation: 24897

Do not wait in a GUI event handler - it prevents the processing of messages, eg. repaint requests.

Nothing GUI gets done while you are waiting on the lock.

Upvotes: 4

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