Java 11: Collectors.toUnmodifiableList

Collect a stream straight into an immutable list.

Code

List<Integer> doubled = Stream.of(1, 2, 3)
        .map(n -> n * 2)
        .collect(Collectors.toUnmodifiableList());
System.out.println(doubled);
try { doubled.add(99); } catch (UnsupportedOperationException e) {
    System.out.println("unmodifiable");
}

Output

[2, 4, 6]
unmodifiable

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Published 2026-07-26