Seems like automatically generated class name. You shouldn't ever see that as a Java developer unless you work for Sun, since this is internal package. The name, though long, seems pretty consistent with the rest of the names in the package [1].

If you look at it once more I guess that it is used as a Painter for MaximizeButton located in InternalFrameTitlePane of InternalFrameTitlePane of InternalFrame.

How would you name such thing?

[1] http://javadoc.bugaco.com/com/sun/java/swing/plaf/nimbus/pac...