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Introduction
The Java HashSet class implements the Set interface, backed by a hash table.Following are the important points about HashSet −
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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.
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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
Sr.No. | Constructor & Description |
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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
Sr.No. | Method & Description |
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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). |
9 | Spliterator<E> spliterator()
This method returns a late-binding and fail-fast Spliterator over the elements in this set. |
Methods inherited
This class inherits methods from the following classes −
- java.util.AbstractSet
- java.util.AbstractCollection
- java.util.Object
- java.util.Set
Adding element to a HashSet Example
The following example shows the usage of Java HashSet add() method to add entries to the HashSet. We”ve created a HashSet object of Integer. Then few entries are added using add() method and then set is printed.
package com.tutorialspoint; import java.util.HashSet; public class HashSetDemo { public static void main(String args[]) { // create hash set HashSet <Integer> newset = new HashSet <>(); // populate hash set newset.add(1); newset.add(2); newset.add(3); // checking elements in hash set System.out.println("Hash set values: "+ newset); } }
Output
Let us compile and run the above program, this will produce the following result.
Hash set values: [1, 2, 3]
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