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javasetjava-streamjava-11collectors

Which Set implementation in Collectors.toSet()?

I have the following code:

Stream.of(1, 4, 5).collect(Collectors.toSet());

From Javadoc of toSet() method one can read:

There are no guarantees on the type (...) of the Set returned

I took a look at the actual implementation of toSet() method and at a first sight it looks like HashSet is always returned (at least in JDK 11).

I know that implementation can change in the future without violation of the contract but is there currently any situation when different implementation than HashSet is returned?

Solution

  • No. The JDK source code clearly shows that Collectors.toSet() always uses HashSet::new. As you say, that may of course change.