Java HashSet

Java HashSet:

java.lang.Object
java.util.AbstractCollection
java.util.AbstractSet
java.util.HashSet

Java HashSet class is used to create a collection that uses a hash table for storage.
Characteristics:

HashSet stores the elements by using a mechanism called hashing.
HashSet contains unique elements only.
HashSet allows null value.
HashSet class is non synchronized.
HashSet doesn't maintain the insertion order. Here, elements are inserted based on their hashcode.
HashSet is the best approach for search operations.
The initial default capacity of HashSet is 16, and the load factor is 0.75.

Note: A list can contain duplicate elements whereas Set contains unique elements only.

Constructors:

HashSet(): It is used to construct a default HashSet.
HashSet(int capacity): It is used to initialize the capacity of the hash set to the given integer value capacity. The capacity grows automatically as elements are added to the HashSet.
HashSet(int capacity, float loadFactor): It is used to initialize the capacity of the hash set to the given integer value capacity and the specified load factor.
HashSet(Collection c): It is used to initialize the hash set by using the elements of the collection c.

Methods:

boolean add(E e):It is used to add the specified element to this set if it is not already present.
Example: set.add("One");

The clone() method of Java HashSet class is used to return a shallow copy of the specified HashSet.
Syntax: public Object clone()
Returns: The clone() method returns a shallow copy of this HashSet.
Example:

HashSet clonedSet = new HashSet();
clonedSet = (HashSet)set.clone();
System.out.println("The new clone: " + clonedSet);

The contains() method of Java HashSet class is used to check if this HashSet contains the specified element or not. It returns true if an element is found otherwise, returns false.
Syntax: public boolean contains(Object o)
Note: o: It is the element whose presence in this set is to be tested.
Returns: The contains() method returns true if this set contains the specified element.
Example: System.out.println("Contains one? :- "+set.contains("one"));

The isEmpty() method of Java HashSet class is used to check whether HashSet contains an element or not. It returns true if the set contains element, otherwise returns false.
Syntax: public boolean isEmpty()
Returns: The isEmpty() method returns true if this set contains no elements.
Example: System.out.println("Is the set empty: "+set.isEmpty());

The remove() is a method of Java HashSet class which removes the specified element from this set if it is present.
Syntax: public boolean remove(Object o)
Note: o: It is the element whose presence in this set is to be tested.
Returns: The remove() method returns true if the set contained the specified element.
Example: set.remove("One");

The size() method of Java HashSet class is used to get the number of elements in this HashSet (its cardinality).
Syntax: Public int size()
Returns: The size() method returns the number of elements present in the HashSet.
Example: System.out.println("The size of the set is: " + set.size());

The iterator() method of Java HashSet class is used to return an iterator of the same elements as the HashSet.
Syntax: public Iterator iterator()
Returns: The iterator() method returns an Iterator over the elements in this set.
Example:

Iterator itr=set.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}