Java.util.HashSet Class


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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
1

HashSet()

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

2

HashSet(Collection<? extends E> c)

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

3

HashSet(int initialCapacity)

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

4

HashSet(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
1

boolean add(E e)

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

2

void clear()

This method removes all of the elements from this set.

3

Object clone()

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

4

boolean contains(Object o)

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

5

boolean isEmpty()

This method returns true if this set contains no elements.

6

Iterator<E> iterator()

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

7

boolean remove(Object o)

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

8

int 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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