Eugene :
How do you create an Unmodifiable List/Set/Map with Collectors.toList/toSet/toMap, since toList (and the like) are document as :
There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned
Before java-10 you have to provide a Function with Collectors.collectingAndThen, for example:
List<Integer> result = Arrays.asList(1, 2, 3, 4)
.stream()
.collect(Collectors.collectingAndThen(
Collectors.toList(),
x -> Collections.unmodifiableList(x)));
Eugene :
With Java 10, this is much easier and a lot more readable:
List<Integer> result = Arrays.asList(1, 2, 3, 4)
.stream()
.collect(Collectors.toUnmodifiableList());
Internally, it's the same thing as Collectors.collectingAndThen, but returns an instance of unmodifiable List that was added in Java 9.
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