A DESCRIPTION OF THE REQUEST :
I'm not sure if this is against the spec, but it's certainly annoying...

The following code snippet returns HashMap$KeySet, which is a subclass of AbstractSet, and thus not Serializable.The parent HashMap object is Serializable though.

{
    Set set = map.keySet();
}

JUSTIFICATION :
Main use case for this is if one wants to store a keySet in a J2EE HttpSession - I could store the HashMap, so why can't I store it's keySet()?

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
HashMap$KeySet implements Serializable
ACTUAL -
HashMap$KeySet extends AbstractSet
(and doesn't implement Serializable)

---------- BEGIN SOURCE ----------
See above - no other need for code example
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
new HashSet( map.keySet() );

Obviously this isn't a good example for performance / efficiency.