Java Language Basics of Set


What is a Set?

A set is a data structure which contains a set of elements with an important property that no two elements in the set are equal.

Types of Set:

  1. HashSet: A set backed by a hash table (actually a HashMap instance)
  2. Linked HashSet: A Set backed by Hash table and linked list, with predictable iteration order
  3. TreeSet: A NavigableSet implementation based on a TreeMap.

Creating a set

Set<Integer> set = new HashSet<Integer>(); // Creates an empty Set of Integers

Set<Integer> linkedHashSet = new LinkedHashSet<Integer>(); //Creates a empty Set of Integers, with predictable iteration order

Adding elements to a Set

Elements can be added to a set using the add() method

 set.add(12); //  - Adds element 12 to the set
 set.add(13); //  - Adds element 13 to the set

Our set after executing this method:

set = [12,13]

Delete all the elements of a Set

set.clear();  //Removes all objects from the collection.

After this set will be:

set = []

Check whether an element is part of the Set

Existence of an element in the set can be checked using the contains() method

set.contains(0);  //Returns true if a specified object is an element within the set.

Output: False

Check whether a Set is empty

isEmpty() method can be used to check whether a Set is empty.

set.isEmpty();  //Returns true if the set has no elements

Output: True

Remove an element from the Set

 set.remove(0); // Removes first occurrence of a specified object from the collection

Check the Size of the Set

set.size(); //Returns the number of elements in the collection

Output: 0