Why Collection Factory Methods? Before Java 9, creating a small immutable collection was tedious: // Java 8 — three lines, two classes, mutable intermediate List<String> names = Collections.unmodifiableList( Arrays.asList("Alice", "Bob", "Charlie") ); // Java 8 — even worse for Map Map<String, Integer> scores = new HashMap<>(); scores.put("Alice", 90); scores.put("Bob", 85); Map<String, Integer> immutableScores = Collections.unmodifiableMap(scores); JEP 269 (Java 9) introduced static factory methods that create truly immutable collections with a single expression: