EnumSet in Java

Pre-requisite: Enum in Java
EnumSet is one of the specialized implementation of Set interface for use with the enumeration type. Few important features of EnumSet are as follows:

• It extends AbstractSet and implements Set Interface in Java.
• EnumSet class is a member of the Java Collections Framework & is not synchronized.
• It’s a high performance set implementation, much faster than HashSet.
• All of the elements in an enum set must come from a single enumeration type that is specified when the set is created either explicitly or implicitly.

Declaration:

public abstract class EnumSet<E extends Enum<E>> 

Here, E specifies the elements. E must extend Enum, which enforces the requirement that the elements must be of specified enum type.

Below program illustrates a few basic functions of EnumSet:

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

Methods in EnumSet:

• EnumSet of(E e1): Creates an enum set initially containing the specified elements.
• EnumSet of(E e11, E el2): Creates an enum set initially containing the specified elements.
• EnumSet of(E e11, E el2, Eel3): Creates an enum set initially containing the specified elements.
• EnumSet of(E e11, E el2, Eel3,E el4….): Creates an enum set initially containing the specified elements.
• EnumSet of(E e1, E rest…): Creates an enum set initially containing the specified elements.
• EnumSet complementOf(EnumSet 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.
• EnumSet allOf(Class elementType): Creates an enum set containing all of the elements in the specified element type.
• EnumSet range(E from, E to): Creates an enum set initially containing all of the elements in the range defined by the two specified endpoints.
• EnumSet copyof(): The method is used to copy all of the contents from a collection to a new enum set.
• EnumSet copyof(EnumSet s): The method is used to copy all of the contents from an existing EnumSet to a new enum set.
• EnumSet clone(): The method is used to return a shallow copy of the existing or this set.
• EnumSet noneOf(): The method is used to create a null set.

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