The description for repaint(long) states:

   Repaints the component. This will result in a call to update
   within tm milliseconds.
 
   Parameters: tm - maximum time in milliseconds before update

This doesn't explain how this method actually works and how it can be used.
Furthermore, it leads to misuderstanding and erroneously written TCK tests.
Please see the eMail thread on this in the Comments section.