RFR(m): 8159404: immutable collections should throw UOE unconditionally

Stuart Marks stuart.marks at oracle.com
Fri Sep 2 01:47:31 UTC 2016

Hi all,

Please review this change to make the immutable collections (List.of, Set.of, 
Map.of) throw UnsupportedOperationException unconditionally. That is, they 
should throw UOE even if a mutator method is called with arguments that make it 
a no-op. Calling a mutator method on an immutable collection is always a 
programming error, and having it sometimes be a no-op potentially leads to errors.

Note that the existing Collections unmodifiable wrappers always throw UOE 
unconditionally. This change makes the immutable collections behave consistently 
with the unmodifiable wrappers. For example,

     List<String> unmodList = Collections.unmodifiableList(new ArrayList<>());
     unmodList.addAll(List.of()); // throws UOE
     List.of().addAll(List.of()); // currently does nothing, change to throw UOE

Unfortunately, various other specialized collections such as emptyList() etc. 
behave differently, e.g.

     Collections.emptyList().addAll(List.of()); // does nothing

However, that change will be left for another day.







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