𝕓𝕣𝕒𝕚𝕟. 𝕜𝕒𝕞𝕚𝕝𝕝𝕠𝕓𝕚𝕟𝕤𝕜𝕚.𝕕𝕖𝕧

Collections Utility Class

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java.util.Collections is a utility class that provides static methods to operate on collections like List, Set, Map.

Methods

List<Integer> nums = Arrays.asList(3, 2, 1);
 
Collections.sort(nums);       // [1, 2, 3]
Collections.shuffle(nums);    // Random order
Collections.reverse(nums);    // Reverses the list
Collections.swap(nums, 0, 2); // Swaps values at index 0 and 2
Collection.max(nums);
Collection.min(nums);
UnmodifiableList
List<String> readOnly = Collections.unmodifiableList(myList);
readOnly.add("X"); // Throws UnsupportedOperationException
SynchronizedList
List<String> syncLIst = Collections.synchronizedList(new ArrayList<>());

Use Cases

  • Sorting leaderboard scores.
  • Shuffling quiz questions.
  • Creating read-only collections (public APIs).
  • Wrapping collections in thread-safe mode (legacy apps).

Tip

Be ready to:

  • use sort(), reverse(), max() in coding rounds,
  • explain the difference between Collections (utility) vs Collection (interface),
  • mention unmodifiableList() when discussing immutability.

Parent: _Collections

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