Java: Immutable copy with List.copyOf

List.copyOf snapshots a collection into an unmodifiable list.

Code

List<Integer> src = new ArrayList<>(List.of(1, 2, 3));
List<Integer> copy = List.copyOf(src);
src.add(4);
System.out.println("src=" + src + " copy=" + copy);

Output

src=[1, 2, 3, 4] copy=[1, 2, 3]

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Published 2026-07-26