Collections Helper Class

List<Integer> nums = new ArrayList<>(List.of(3, 1, 4, 1, 5, 9));

// 1. Reordering & In-Place Sorting
Collections.sort(nums); // [1, 1, 3, 4, 5, 9]
Collections.sort(nums, Comparator.reverseOrder());
Collections.reverse(nums);
Collections.shuffle(nums);
Collections.swap(nums, 0, 1);

// 2. Metrics & Binary Search
int max = Collections.max(nums); // 9
int min = Collections.min(nums); // 1
int freq = Collections.frequency(nums, 1); // 2
int idx = Collections.binarySearch(nums, 4); // Must be sorted first

// 3. Disjoint Verification
boolean noOverlap = Collections.disjoint(nums, List.of(99, 100)); // true

// 4. Convenience Factories
List<String> empty = Collections.emptyList();
List<String> single = Collections.singletonList("only_one");
List<Integer> zeroes = Collections.nCopies(5, 0); // [0, 0, 0, 0, 0]

List<Integer> list = new ArrayList<>(List.of(30, 10, 20));

// 1. Natural ascending order
Collections.sort(list); // [10, 20, 30]
list.sort(Comparator.naturalOrder());

// 2. Reverse order
Collections.sort(list, Comparator.reverseOrder()); // [30, 20, 10]
list.sort(Comparator.reverseOrder());

// 3. Object field comparator via method reference
List<Student> students = new ArrayList<>(...);
students.sort(Comparator.comparing(Student::getMarks));

// 4. Reversed object comparison
students.sort(Comparator.comparing(Student::getMarks).reversed());

// 5. Multi-level comparator chaining (sort by marks, then tiebreak by name)
students.sort(
    Comparator.comparing(Student::getMarks)
              .thenComparing(Student::getName)
);

List<String> mutable = new ArrayList<>(List.of("alpha", "beta"));

// Read-only view wrapper
List<String> unmodifiable = Collections.unmodifiableList(mutable);
// unmodifiable.add("gamma"); // Throws UnsupportedOperationException!

// Thread-safe synchronized wrapper (coarse-grained lock)
List<String> synchronizedList = Collections.synchronizedList(mutable);

List<Integer> list = List.of(1, 2, 3);
Set<String> set = Set.of("A", "B", "C");
Map<Integer, String> map = Map.of(
    1, "Alice",
    2, "Bob"
);