A DESCRIPTION OF THE REQUEST :
When setting the icon for a window there are a couple of limitations:
1) You can't set multiple sizes. So, the same icon is used in the task bar (16x16) and when the user Alt-Tabs (32x32). As a developer, you have to make a choice as to which one of these will be ugly.
2) You can't set transparent icons. Using PNG with an alpha channel results in very ugly icons.

JUSTIFICATION :
In order for Java applications to truly co-exist on a platform, they have to look nice. The current implementation makes them appear unprofessional. As a result, we have to write native code to fix these problems.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
First, icons should support transparency.

Second, perhaps a new image format that can include multiple images of different sizes should be supported.
ACTUAL -
I am forced to create opaque icons. Then, I create a 16x16 for the task bar, but when the user presses Alt-Tab, a 32x32 icon is displayed, which is just scaled up from 16x16. If, instead, I use a 32x32 icon, the task bar icon looks terrible.

---------- BEGIN SOURCE ----------
JFrame frame = new JFrame().
frame.setIconImage(/* pass a transparent PNG */);

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Native code.
Additional problems being fixed:
- Dialog don't always inherit icon from parent frame on XAWT
- Ownerless dialogs always displays an unmodifiable "coffee cup" icon 
(see description of 6317332 for details)