Java.util.HashSet Class

Java.util.HashSet Class

Introduction

The java.util.HashSet class implements the Set interface, backed by a hash table.Following are the important points about HashSet:

  • This class makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time.
  • This class permits the null element.

Class declaration

Following is the declaration for java.util.HashSet class:

public class HashSet<E>
   extends AbstractSet<E>
   implements Set<E>, Cloneable, Serializable

Parameters

Following is the parameter for java.util.HashSet class:

  • E — This is the type of elements maintained by this set.

Class constructors

S.N.Constructor & Description
1HashSet()

This constructs a new, empty set; the backing HashMap instance has default initial capacity (16) and load factor (0.75).

2HashSet(Collection<? extends E> c)

This constructs a new set containing the elements in the specified collection.

3HashSet(int initialCapacity)

This constructs a new, empty set; the backing HashMap instance has the specified initial capacity and default load factor (0.75).

4HashSet(int initialCapacity, float loadFactor)

This constructs a new, empty set; the backing HashMap instance has the specified initial capacity and the specified load factor.

Class methods

S.N.Method & Description
1boolean add(E e)

This method adds the specified element to this set if it is not already present.

2void clear()

This method removes all of the elements from this set.

3Object clone()

This method returns a shallow copy of this HashSet instance, the elements themselves are not cloned.

4boolean contains(Object o)

This method returns true if this set contains the specified element.

5boolean isEmpty()

This method returns true if this set contains no elements.

6Iterator<E> iterator()

This method returns an iterator over the elements in this set.

7boolean remove(Object o)

This method removes the specified element from this set if it is present.

8int size()

This method returns returns the number of elements in this set(its cardinality).

Methods inherited

This class inherits methods from the following classes:

  • java.util.AbstractSet
  • java.util.AbstractCollection
  • java.util.Object
  • java.util.Set

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