Set

(Set don't allow duplicate values)

The set interface is present in java.util package and extends the Collection interface is an unordered collection of objects in which duplicate values cannot be stored. It is an interface that implements the mathematical set. This interface contains the methods inherited from the Collection interface and adds a feature that restricts the insertion of the duplicate elements. There are two interfaces that extend the set implementation namely SortedSet and NavigableSet.

Instantiate

Set<datatype> set = new HashSet <datatype, datatype> ();

Set<datatype> set = new TreeSet <datatype, datatype> (); //(sorted Set) - all the elements are sorted in ascending order

Set<datatype> set = new LinkedHashSet <datatype, datatype> (); //ordered collection of set, data is stored and retrieved in the same order

Methods (map)

• add() - to insert value in set

  set.add(element);

  //This method is used to append all of the elements from the mentioned collection

  to the existing set. The elements are added randomly without following any specific order.

  set.addAll(collection);

• clear() - This method is used to remove all the elements from the set but not delete the set. The reference for the set still exists.

  set.clear(key);

• contains() - This method is used to check whether a specific element is present in the Set or not.

  set.contains(element);

• isEmpty() - This method is used to check whether the set is empty or not.

  set.isEmpty();

• containsKey() - returns true if key is present in the map

  boolean map.containsKey(key);

• remove() - This method is used to remove the given element from the set. This method returns True if the specified element is present in the Set otherwise it returns False.

  set.remove(element);

• size() - This method is used to get the size of the set. This returns an integer value which signifies the number of elements.

  int n = set.size();

• toArray() - This method is used to form an array of the same elements as that of the Set.

  Object[] arr = set.toArray();

• retainAll() - This method is used to remove all the elements from the collection which are present in the set.

  set.retainAll(collection);