MouseListener MouseDragged无法按预期工作

I have a grid where the boxes become red (I basically want to paint the grid) when I left click, hold and move the cursor on them (i.e: drag mouse). I have the code below. When I do the mouse dragging. The MouseDragged method is called properly however only one box becomes red and nothing happens while I drag after that (although the method is still called). Any ideas ? Hope I was clear. ThanksI have a grid where the boxes become red (I bas