Thanks a lot! There is another question: Is it the absolute way to create a thread  handling the game loop seperately? other words, could I make the game loop without using thread programming?

[size=10pt][size=10pt][size=10pt][size=10pt][size=10pt]Generally,the game loop is built up manually,hower, in my opioin, the game application under awt or swing doesn't need to do this ,since we can override the  defult method Update() with game logic (sprite move and collosion detect ,etc) and Paint() with code of graphic rendering ,and finally we just call Repaint()  iteratively within a dead loop while(){} .
so, what's the necessity of constructing a game loop by ourself?[/size][/size][/size][/size][/size]