instanceof UnmodifiableList<?>

[bigBA]

Hi,

i have a method which gets some kind of output from a data call and in case that output is a List<?> turns it into an UnmodifiableList.


if (callOutput instanceof List<?>)
{
callOutput = Collections.unmodifiableList((List<? extends Object>) callOutput);
}


now i would like add the check if callOutput isn't already an instance of UnmodifiableList<?>.

Has anyone an idea how to it?

instanceof UnmodifiableList does not work because UnmodifiableList is declared as inner class of java.util.Collections without any visibility modifier and therefor not public.

[dlorde]

Interesting question...

The class of the unmodifiable list is accessible via getClass(), but there are two kinds of unmodifiable list (random access or non-random access) that may be returned by Collections, so my best guess would be:if (!callOutput.getClass().getName().contains("Unmodifiable")) {
callOutput = Collections.unmodifiableList(callOutput);
}It might be best to stick this into a utility method somewhere, e.g. ensureReadOnly(..), or something.

It's a bit of a hack, but I've seen worse ;-)

Any programming problem can be solved by adding a level of indirection...
Anon.

[bigBA]

Yeah.. hm. I'll have to check if this has too much impact in the performance.

In the mean time i had to adjust the existing instanceof into
callOutput.getClass() == ArrayList.class
because we also have cusomt lists which extend ArrayList and which would loose added methods if stored inside an unmodifiable list...

Well, and here we go.. implementing a custom UnmodifiableList (extend it) isn't possible *thumbsup* :)