The answer is already given by Jonas (use a Swing timer), but it might be useful to explain why you are not seeing the animation, and why the timer is the best solution for this problem.
Why do I not see the different repaints
When you call JComponent#repaint
the JComponent
is not repainted. Instead, an asynchronous request to repaint a certain component is scheduled on the EDT. If you invoke many repaint
calls, Swing might decide to group those requests and repaint the component just once.
I did not immediately found an official reference for this in the Oracle documentation (the Swing painting article does not seem to mention it). The only place where I found this was in a note in this article, but I am pretty certain this is documented somewhere.
Why is using a Timer
the best solution
For an animation, you basically want to say:
my character should move x
pixels in y
milliseconds
And preferably, you want to have a smooth animation on screen so you need to repaint rather frequently. If you keep in mind that
- All interaction with the Swing components should happen on the EDT (Event Dispatch Thread, see the Concurrency in Swing article for more info)
- You should never block the EDT as this will freeze your UI, meaning you cannot 'wait' in the EDT until a repaint is done or the repaint will never happen
- Repaint requests can be grouped, so calling repaint
x
times does not guarantee you that your paint
method is called x
times as well
The solution to overcome this limitations is to use a Timer
. With the same example (moving a character on screen), you can use a Timer
to update the position of the character and schedule a repaint. Since the Timer
code is triggered on the EDT, you do not violate the Swing threading rules.
In the paintComponent
method of your component, you then paint the character at the current location. This might be the 'previous location + 1', or the 'previous location +2' (or ...) depending on how many times the Timer
has been triggered between the previous paint
call and the current paint
call. This ensures the speed at which your character moves is system-independent. Only the smoothness of the animation will depend on your system (as in: how many repaint requests get grouped).
The Swing Timer
tutorial to which Jonas already linked contains more information.
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