The current spec for Frame.setExtendedState() states:

   Note that if the state is not supported on a given platform, nothing will
   happen. The application may determine if a specific state is available via
   the java.awt.Toolkit#isFrameStateSupported(int state) method.

It's unclear what "nothing will happen" mean - in particular, whether
the value of the state property (as returned by getExtendedState()) will
also not change if the particular state is unsupported.

Also, it seems that the @see link to that Toolkit method is incorrect.

###@###.### 2005-03-01 18:13:29 GMT

Additionally, according to Denis, only the negative result of the Toolkit check
is 100% correct; if isFrameStateSupported() returns true, the window management
system may still not support the requested state. This should also be made clear
in the spec.