What are the various changes that the Collection Framework underwent recently?

Recent Changes in Java Collection Framework (Java 8 to Java 21)

The Java Collection Framework has undergone several improvements in recent versions (Java 8 onward) to enhance performance, usability, and convenience. Here’s a summary of major updates:

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1. Java 8 – Lambda & Streams (2014)

Introduced functional programming features.

Key Additions:

• forEach() method in Iterable
  Example: list.forEach(item -> System.out.println(item));
• Streams API
  Allows filtering, mapping, and reducing collections easily. list.stream().filter(x -> x.startsWith("A")).forEach(System.out::println);
• Default methods in interfaces like List, Set, Map.

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2. Java 9 – Convenience Factory Methods (2017)

Key Additions:

• Immutable collections using List.of(), Set.of(), Map.of() List<String> list = List.of("a", "b", "c");
• Stream.iterate() enhancements with a predicate.
• Improved Optional methods like ifPresentOrElse().

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3. Java 10 – var Keyword (2018)

Though not a Collection feature directly, var simplified collection declarations:

var list = List.of("x", "y");

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4. Java 11 to Java 14

• Small improvements and performance optimizations.
• New toArray(IntFunction) method: String[] arr = list.toArray(String[]::new);

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5. Java 16 – Collectors.toUnmodifiableList()

Used with streams to collect elements into an unmodifiable list:

List<String> unmodList = list.stream()
                             .collect(Collectors.toUnmodifiableList());

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6. Java 17 to Java 21

Mostly internal improvements and pattern matching support:

• Performance updates for concurrent collections.
• Preview features for pattern matching on instanceof (useful in filtering).
• Sequenced collections and Map.entry() enhancements.

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Summary of Major Enhancements:

Version	Changes
Java 8	Lambda expressions, Streams, forEach()
Java 9	Factory methods: List.of(), Set.of(), Map.of()
Java 10	var keyword for type inference
Java 11+	Better toArray(), new Collectors methods
Java 16+	toUnmodifiableList(), internal performance boosts
Java 17+	Pattern matching, sequenced collections (in progress)