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EnumSet in Java

Last Updated : 25 Apr, 2026

In Java, the EnumSet is a specialized set implementation for use with enum types. It is a part of java.util package and provides a highly optimized set for storing enum constants. The EnumSet is one of the specialized implementations of the Set interface for use with the enumeration type.

EnumSet is highly efficient and faster for enum types
All of the elements in an EnumSet must come from a single enumeration type that is specified when the set is created either explicitly or implicitly.
It does not allow null elements and throws NullPointerException if we do so.
EnumSet uses a weakly consistent iterator, not a fail-fast one—so it doesn’t throw ConcurrentModificationException and may reflect some modifications during iteration.

Java

import java.util.EnumSet;

enum Student { Geek1, Geek2, Geek3, Geek4, Geek5 }

public class Geeks {
    public static void main(String[] args) {
        
        // Create an EnumSet containing specific elements
        EnumSet<Student> e = EnumSet.of(Student.Geek1, Student.Geek2, Student.Geek3);

        System.out.println("EnumSet: " + e);
    }
}

Output

EnumSet: [Geek1, Geek2, Geek3]

Hierarchy of EnumSet

The EnumSet class extends AbstractSet and implements the Set interface, forming part of the Java Collections Framework hierarchy designed specifically for enum types.

Declaration of EnumSet

In Java, the declaration of EnumSet can be done as:

EnumSet<Type> name = EnumSet.of(Element1, Element2, Element3);

Parameter: EnumSet.of() take one or more enum constants as arguments and specifying which enum values to include in the set.
Return Type: It returns a set containing the specified enum constants

Methods

Method	Action Performed
allOf(Class<E> elementType)	Creates an enum set containing all of the elements in the specified element type.
clone()	Returns a copy of this set.
complementOf(EnumSet<E> s)	Creates an enum set with the same element type as the specified enum set, initially containing all the elements of this type that are not contained in the specified set.
copyOf(Collection<E> c)	Creates an enum set initialized from the specified collection.
copyOf(EnumSet<E> s)	Creates an enum set with the same element type as the specified enum set, initially containing the same elements (if any).
noneOf(Class<E> elementType)	Creates an empty enum set with the specified element type.
of(E e)	Creates an enum set initially containing the specified element.
of(E e1, E e2)	Creates an enum set initially containing the specified elements.
of(E first, E… rest)	Creates an enum set initially containing the specified elements.
of(E e1, E e2, E e3)	Creates an enum set initially containing the specified elements.
of(E e1, E e2, E e3, E e4)	Creates an enum set initially containing the specified elements.
of(E e1, E e2, E e3, E e4, E e5)	Creates an enum set initially containing the specified elements.
range(E from, E to)	Creates an enum set initially containing all of the elements in the range defined by the two specified endpoints.

Example: This example demonstrates how to create and manipulate EnumSet using methods like of(), complementOf(), allOf() and range() with enum constants.

Java

import java.util.EnumSet;

// Enum
enum e { CODE, LEARN, CONTRIBUTE, QUIZ, MCQ };


public class Geeks {


    public static void main(String[] args) {

        // Creating a set
        EnumSet<e> s1, s2, s3, s4;

        // Adding elements
        s1 = EnumSet.of(e.QUIZ, e.CONTRIBUTE,
                         e.LEARN, e.CODE);
        s2 = EnumSet.complementOf(s1);
        s3 = EnumSet.allOf(e.class);
        s4 = EnumSet.range(e.CODE, e.CONTRIBUTE);

        // Printing corresponding elements in Sets
        System.out.println("Set 1: " + s1);
        System.out.println("Set 2: " + s2);
        System.out.println("Set 3: " + s3);
        System.out.println("Set 4: " + s4);
    }
}

Output

Set 1: [CODE, LEARN, CONTRIBUTE, QUIZ]
Set 2: [MCQ]
Set 3: [CODE, LEARN, CONTRIBUTE, QUIZ, MCQ]
Set 4: [CODE, LEARN, CONTRIBUTE]

Creating a EnumSet

In Java, EnumSet is an abstract class, we can not directly create an instance of it. Instead it provides static factory methods to create instances. There are two different internal implementations of EnumSet which are listed below:

RegularEnumSet: It uses a single long object to store the elements of the EnumSet. Each bit in the long value represents an enum constant. The size of a long is 64 bits, RegularEnumSet can store up to 64 enum values.
JumboEnumSet: It uses an array of long values to store the elements of the EnumSet. The key difference is that JumboEnumSet allows storing more than 64 values by using multiple long elements to represent a larger set of enum constants.

Note: These are package-private and backed by a bit vector.

Factory Method for EnumSet Creation

Methods	Description
EnumSet.allOf(Class<E> elementType)	Creates an EnumSet containing all the enum constants of the specified enum type
EnumSet.noneOf(Class<E> elementType)	Creates an empty EnumSet
EnumSet.range(E from, E to)	Creates an EnumSet containing the elements from from to to (inclusive)
EnumSet.of(E..... elements )	Creates an EnumSet containing the specified enum constants.

Implementation of Internal Logic

If the number of elements (universe.length) is less than or equal to 64, RegularEnumSet is used otherwise JumboEnumSet is used for larger enum types.

if (universe.length <= 64)
return new RegularEnumSet<>(elementType, universe);
else
return new JumboEnumSet<>(elementType, universe);

Example: This example demonstrates how to create an EnumSet using the EnumSet.allOf() method and print sites contents.

Java

import java.util.*;

class Geeks {

    // Enum
    enum Game { CRICKET, HOCKEY, TENNIS }

    public static void main(String[] args)
    {

        // Creating an EnumSet using allOf()
        EnumSet<Game> g = EnumSet.allOf(Game.class);

        // Printing EnumSet elements to the console
        System.out.println("EnumSet: " + g);
    }
}

Output

EnumSet: [CRICKET, HOCKEY, TENNIS]

Operations on EnumSet

1. Adding Elements

We can use add() and addAll() to insert elements to an EnumSet.

Java

import java.util.EnumSet;

class Geeks {

    // Enum
    enum Game { CRICKET, HOCKEY, TENNIS }

    public static void main(String[] args)
    {

        // Creating an EnumSet
        // using allOf()
        EnumSet<Game> g1 = EnumSet.allOf(Game.class);

        // Creating an EnumSet
        // using noneOf()
        EnumSet<Game> g2 = EnumSet.noneOf(Game.class);

        // Using add() method
        g2.add(Game.HOCKEY);

        // Printing the elements to the console
        System.out.println("EnumSet Using add(): " + g2);

        // Using addAll() method
        g2.addAll(g1);

        // Printing the elements to the console
        System.out.println("EnumSet Using addAll(): " + g2);
    }
}

Output

EnumSet Using add(): [HOCKEY]
EnumSet Using addAll(): [CRICKET, HOCKEY, TENNIS]

2. Accessing Elements:

We can access the EnumSet using the iterator() method.

Java

import java.util.EnumSet;
import java.util.Iterator;

class Geeks {

    // Enum
    enum Game { CRICKET, HOCKEY, TENNIS }

    public static void main(String[] args)
    {
        // Creating an EnumSet using allOf()
        EnumSet<Game> g = EnumSet.allOf(Game.class);

        // Creating an iterator on games
        Iterator<Game> i = g.iterator();

        System.out.print("EnumSet: ");

        while (i.hasNext()) {

            // Iterating and printing elements to
            // the console using next() method

            System.out.print(i.next());
            System.out.print(", ");
        }
    }
}

Output

EnumSet: CRICKET, HOCKEY, TENNIS,

3. Removing Elements

We can use the remove() and removeAll() to remove elements from an EnumSet.

Java

import java.util.EnumSet;

class Geeks {

    // Enum
    enum Game { CRICKET, HOCKEY, TENNIS }

    public static void main(String[] args)
    {
        // Creating EnumSet using allOf()
        EnumSet<Game> g = EnumSet.allOf(Game.class);

        // Printing the EnumSet
        System.out.println("EnumSet: " + g);

        // Using remove()
        boolean b = g.remove(Game.CRICKET);

        System.out.println("Is CRICKET removed? " + b);

        // Using removeAll() and storing the boolean result
        boolean b2 = g.removeAll(g);

        System.out.println("Are all elements removed? "
                           + b2);
    }
}

Output

EnumSet: [CRICKET, HOCKEY, TENNIS]
Is CRICKET removed? true
Are all elements removed? true

Some other methods of classes or interfaces are defined below that somehow helps us to get a better understanding of AbstractSet Class as follows:

Methods Declared in Class java.util.AbstractSet

Method	Description
equals(Object o)	Compares the specified object with this set for equality.
hashCode()	Returns the hash code value for this set.
removeAll(Collection<?> c)	Removes from this set all of its elements that are contained in the specified collection (optional operation).

Methods Declared in Interface java.util.Collection

Method	Description
parallelStream()	Returns a possibly parallel Stream with this collection as its source.
removeIf(Predicate<? super E> filter)	Removes all of the elements of this collection that satisfy the given predicate.
stream()	Returns a sequential Stream with this collection as its source.
toArray(IntFunction<T[]> generator)	Returns an array containing all of the elements in this collection, using the provided generator function to allocate the returned array.

Methods Declared in Interface java.lang.Iterable

Method	Description
forEach(Consumer<? super T> action)	Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.

Methods Declared in Interface java.util.Set

Method	Description
add(E e)	Adds the specified element to this set if it is not already present (optional operation).
addAll(Collection<? extends E> c)	Adds the specified element to this set if it is not already present (optional operation).
clear()	Removes all of the elements from this set (optional operation).
contains(Object o)	Returns true if this set contains the specified element.
containsAll(Collection<?> c)	Returns true if this set contains all of the elements of the specified collection.
isEmpty()	Returns true if this set contains no elements.
iterator()	Returns an iterator over the elements in this set.
remove(Object o)	Removes the specified element from this set if it is present (optional operation).
retainAll(Collection<?> c)	Retains only the elements in this set that are contained in the specified collection (optional operation).
size()	Returns the number of elements in this set (its cardinality).
spliterator()	Creates a Spliterator over the elements in this set.
toArray()	Returns an array containing all of the elements in this set.
toArray(T[] a)	Returns an array containing all of the elements in this set; the runtime type of the returned array is that of the specified array

Methods Declared in Class java.util.AbstractCollection

Method	Description
add(E e)	Ensures that this collection contains the specified element (optional operation).
addAll(Collection<? extends E> c)	Adds all of the elements in the specified collection to this collection (optional operation).
clear()	Removes all of the elements from this collection (optional operation).
contains(Object o)	Returns true if this collection contains the specified element.
containsAll(Collection<?> c)	Returns true if this collection contains all of the elements in the specified collection.
isEmpty()	Returns true if this collection contains no elements.
iterator()	Returns an iterator over the elements contained in this collection.
remove(Object o)	Removes a single instance of the specified element from this collection, if it is present (optional operation).
retainAll(Collection<?> c)	Retains only the elements in this collection that are contained in the specified collection (optional operation).
toArray()	Returns an array containing all of the elements in this collection.
toArray(T[] a)	Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
toString()	Returns a string representation of this collection.

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