What is the Collections utility class in Java?

The Collections utility class provides static methods for operating on collections. Key methods: sort(list) and sort(list, comparator) for sorting, binarySearch(list, key) for searching (requires sorted list), reverse(list), shuffle(list), min(collection) and max(collection), frequency(collection, obj), unmodifiableList(list) (returns read-only view), synchronizedList(list) (returns thread-safe view), emptyList()/singleton(obj) for immutable utility collections, nCopies(n, obj) for a list of n copies. These methods save you from reimplementing common algorithms and promote code reuse with existing collections.