Immutable map creation
Code Comparison
Map<String, Integer> map = new HashMap<>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
map = Collections.unmodifiableMap(map);
Map<String, Integer> map =
Map.of("a", 1, "b", 2, "c", 3);
Why the modern way wins
📏
Inline creation
No temporary mutable map needed.
🔒
Immutable result
The map cannot be modified after creation.
🚫
No null keys/values
Null entries are rejected immediately.
Old Approach
Map Builder Pattern
JDK Support
Immutable map creation
Available
Widely available since JDK 9 (Sept 2017)
How it works
Map.of() accepts key-value pairs inline and returns an immutable map. For more than 10 entries, use Map.ofEntries() with Map.entry() pairs.
Related Documentation
Proof