Immutable set creation

Code Comparison

Set<String> set =
    Collections.unmodifiableSet(
        new HashSet<>(
            Arrays.asList("a", "b", "c")
        )
    );

Set<String> set =
    Set.of("a", "b", "c");

Why the modern way wins

📏

One line instead of three nested calls.

🚫

Throws if you accidentally pass duplicate elements.

🔒

No add/remove possible after creation.

Old Approach

Verbose Wrapping

JDK Support

Immutable set creation

Available

Widely available since JDK 9 (Sept 2017)

How it works

Set.of() creates a truly immutable set that rejects nulls and duplicate elements at creation time. No more wrapping mutable sets.