displayable.setFullScreenMode(true);
Device: Motorola V525 (May affect other Motorola handsets).
Problem: Only paints in area not used by softbuttons, even if no softbuttons are used, so you get a white non-repainted area along the bottom of the screen.
Solution: Override displayable.getHeight() and +10 to the result of the normal method. This should then give you proper fullscreen.
Sorry, I can't think of anything else to choose offhand. Someone else can choose another method.
Surely that is a problem with getHeight() not accounting for the screensize change

Incidentally, the more durable way of handling this issue on the Motorolas, is to listen for the sizeChanged(...) callback method. (as not all motorolas have a softkey bar height of 10 pixels)
It receives the correct canvas dimensions in its parameters.
Going back to the original method :-
displayable.setFullScreenMode(true);
Device: LGC2200
Problem: throws a NullPointerException if called within the Canvas constructor.
Solution: call it after the Canvas has been constructed & made the current displayable.
Next method :-
javax.microedition.lcdui.Graphics.drawRect(int, int, int, int)