java.util · java.base · since Java 1.4

LinkedHashSet

declaration
public class LinkedHashSet<E> extends HashSet<E>
        implements SequencedSet<E>, Cloneable, Serializable

HashSet plus a linked list through the entries: O(1) operations with predictable insertion-order iteration.

  • The deterministic-order upgrade when tests or users see the iteration

Key methods

LinkedHashSet(int initialCapacity)Presize like HashSet; insertion order is preserved regardless of capacity.
static <E> LinkedHashSet<E> newLinkedHashSet(int numElements)Correctly presized factory (Java 19+).