[amorgang],
I don't quite understand what you are asking. The isDoubleBuffered() method of javax.microedition.lcdui.Canvas class is stated in the API documentation clearly. isDoubleBuffered() returns true is the Graphics is double buffered by the implementation and false otherwise.
I'll be glad to help if you can provide more information of the issue you are encountering or even better if you can attach the source code to this posting.
HTH.
Allen Lai
Developer Technical Support
SUN Microsystems
http://www.sun.com/developers/support/