HashSet in java

HashSet in java

Java HashSet is an collection class which implements Set interface. It is an    un-ordered collection means insertion order is not followed of object in which duplicate value are not allowed.

HashSet class Declaration

public class HashSet

    extends AbstractSet

    implements Set, Cloneable, java.io.Serializable { …}

Features of Hashset class

1. HashSet stores unique element only. Duplicate element not allowed if we enter then recent one get override by previous one.
2. HashSet uses hashing mechanism to store unique element.
3. HashSet does not maintain insertion order because element are stored on the basis of hashing technique.
4. HashSet allows null value.
5. Hashset class is not thread safe, It means it is non synchronized.
6. HashSet is best choice when we perform search operation.

Constructor and Description

HashSet hs = new HashSet();     

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

HashSet hs = new HashSet<>(int initialCapacity);

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

HashSet hs = new HashSet(int initialCapacity, float loadFactor)

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

HashSet hs = new HashSet(Collection<? extends E> c)

Constructs a new set containing the elements in the specified collection.

Java HashSet Example

import java.util.HashSet;

import java.util.Iterator;

public class HashSetDemo {

     public static void main(String[] args) {

    

           HashSet hs = new HashSet();

           hs.add(345);

           hs.add("abc");

           hs.add(123);

           hs.add("veer");

           hs.add(null);       

           hs.add("veer");

           hs.add("aaa");

          

           /* check element and size */

           System.out.println(hs);

           System.out.println("Size is: "+hs.size());

               

         System.out.println("--------------------------");

          

         // Iterating each element

         Iterator itr = hs.iterator();

         while(itr.hasNext()){

         Object obj = itr.next();

         System.out.println(obj);

         }

        

     }

}

Output

[null, aaa, abc, 345, 123, veer]

Size is: 6

--------------------------

null

aaa

abc

345

123

veer

From above output we can see duplicate value are not allowed and Also insertion order is not followed.