Java 10: Collecting a Stream into an Unmodifiable Collection

Fahd ShariffJune 4th, 2018Last Updated: June 4th, 2018

0 18 1 minute read

Java 10 introduces several new methods to facilitate the creation of unmodifiable collections.

The List.copyOf, Set.copyOf, and Map.copyOf methods create new collection instances from existing instances. For example:

List<String> modifiable = Arrays.asList("foo", "bar");
List<String> unmodifiableCopy = List.copyOf(list);

// Note that since Java 9, you can also use "of" to create
// unmodifiable collections
List<String> unmodifiable = List.of("foo", "bar");

There are also new collector methods, toUnmodifiableList, toUnmodifiableSet, and toUnmodifiableMap, to allow the elements of a stream to be collected into an unmodifiable collection. For example:

// Java 10
Stream.of("foo", "bar").collect(toUnmodifiableList());

// before Java 10
Stream.of("foo", "bar").collect(
    collectingAndThen(toList(), Collections::unmodifiableList));

Published on Java Code Geeks with permission by Fahd Shariff, partner at our JCG program. See the original article here: Java 10: Collecting a Stream into an Unmodifiable Collection

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