Package edu.stanford.nlp.util

Class IdentityHashSet<E>

  • All Implemented Interfaces:
    Serializable, Cloneable, Iterable<E>, Collection<E>, Set<E>
    public class IdentityHashSet<E>
extends AbstractSet<E>
implements Cloneable, Serializable
    This class provides a IdentityHashMap-backed implementation of the Set interface. This means that whether an object is an element of the set depends on whether it is == (rather than equals()) to an element of the set. This is different from a normal HashSet, where set membership depends on equals(), rather than ==. Each element in the set is a key in the backing IdentityHashMap; each key maps to a static token, denoting that the key does, in fact, exist. Most operations are O(1), assuming no hash collisions. In the worst case (where all hashes collide), operations are O(n).
    Author:
    Bill MacCartney
    See Also:
    Serialized Form

    • Constructor Detail

      • IdentityHashSet

        public IdentityHashSet()
        Construct a new, empty IdentityHashSet whose backing IdentityHashMap has the default expected maximum size (21);

      • IdentityHashSet

        public IdentityHashSet​(int expectedMaxSize)
        Construct a new, empty IdentityHashSet whose backing IdentityHashMap has the specified expected maximum size. Putting more than the expected number of elements into the set may cause the internal data structure to grow, which may be somewhat time-consuming.
        Parameters:
        expectedMaxSize - the expected maximum size of the set.

      • IdentityHashSet

        public IdentityHashSet​(Collection<? extends E> c)
        Construct a new IdentityHashSet with the same elements as the supplied Collection (eliminating any duplicates, of course); the backing IdentityHashMap will have the default expected maximum size (21).
        Parameters:
        c - a Collection containing the elements with which this set will be initialized.

    • Method Detail

      • add

        public boolean add​(E o)
        Adds the specified element to this set if it is not already present. Remember that this set implementation uses == (not equals()) to test whether an element is present in the set.
        Specified by:
        add in interface Collection<E>
        Specified by:
        add in interface Set<E>
        Overrides:
        add in class AbstractCollection<E>
        Parameters:
        o - element to add to this set
        Returns:
        true if the element was added, false otherwise

      • clone

        public Object clone()
        Returns a shallow copy of this IdentityHashSet instance: the elements themselves are not cloned.
        Overrides:
        clone in class Object
        Returns:
        a shallow copy of this set.

      • contains

        public boolean contains​(Object o)
        Returns true if this set contains the specified element. Remember that this set implementation uses == (not equals()) to test whether an element is present in the set.
        Specified by:
        contains in interface Collection<E>
        Specified by:
        contains in interface Set<E>
        Overrides:
        contains in class AbstractCollection<E>
        Parameters:
        o - Element whose presence in this set is to be tested.
        Returns:
        true if this set contains the specified element.

      • isEmpty

        public boolean isEmpty()
        Returns true if this set contains no elements.
        Specified by:
        isEmpty in interface Collection<E>
        Specified by:
        isEmpty in interface Set<E>
        Overrides:
        isEmpty in class AbstractCollection<E>
        Returns:
        true if this set contains no elements.

      • remove

        public boolean remove​(Object o)
        Removes the specified element from this set if it is present. Remember that this set implementation uses == (not equals()) to test whether an element is present in the set.
        Specified by:
        remove in interface Collection<E>
        Specified by:
        remove in interface Set<E>
        Overrides:
        remove in class AbstractCollection<E>
        Parameters:
        o - Object to be removed from this set, if present.
        Returns:
        true if the set contained the specified element.

      • size

        public int size()
        Returns the number of elements in this set (its cardinality).
        Specified by:
        size in interface Collection<E>
        Specified by:
        size in interface Set<E>
        Specified by:
        size in class AbstractCollection<E>
        Returns:
        the number of elements in this set (its cardinality).

      • main

        public static void main​(String[] args)
        Just for testing.