Enum vs EnumSet in Java

In this post, we will learn the difference between Enum and EnumSet in Java. This is a frequently asked question in Java interviews for beginners. Let's dive into it.

Enum in Java 

Enum in Java is a data type that contains a fixed set of constants. They are used when we know all possible values at compile time, such as choices on a menu, rounding modes, command line flags, etc.

Here's an example of an Enum in Java:

public enum Days {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
}

Enums in Java are type-safe and have their own namespace. They can be used in switch statements and can have fields, methods, and constructors.

EnumSet in Java 

Java's EnumSet is one of the high-performance Java Collections for enum types. It combines the richness and safety of the Set interface with speed and compactness, as internally it's represented as a bit vector.

Here's how you create an EnumSet in Java:

EnumSet<Days> weekend = EnumSet.of(Days.SATURDAY, Days.SUNDAY);

EnumSet has all the richness of the Collection framework, like Iterator and Stream support, plus specialized methods like complementOf(), copyOf(), noneOf(), and more. 

Difference between "Enum" and "EnumSet" in Java

Feature	Enum	EnumSet
Purpose	Represents a fixed set of constants.	Specialized Set implementation for enums.
Type	Enum is a special type of class in Java.	EnumSet is a regular class in Java.
Declaration	Enums are declared using the "enum" keyword.	EnumSets are created using static factory methods in EnumSet class.
Elements	Enum can have a fixed set of constant values (enum constants).	EnumSet can contain multiple enum constants from the same enum type.
Set Operations	Enum doesn't provide built-in set operations.	EnumSet provides set operations like union, intersection, and complement.
Element Order	Enum elements follow the order of declaration.	EnumSet does not maintain any specific order for elements.
Iteration	Enum elements can be iterated using the "values()" method.	EnumSet elements can be iterated using an iterator or for-each loop.
Bit Vector Representation	Enum constants are internally represented using an integer-based index.	EnumSet internally uses a bit vector representation for efficiency.
Performance	Enum access is generally faster due to their internal representation.	EnumSet is optimized for performance when dealing with small sets of enum constants.
Custom EnumSets	It is not possible to create a custom Enum in Java.	Custom EnumSets can be created using the "of()" or "copyOf()" methods in EnumSet class.

Conclusion 

Enum and EnumSet in Java are powerful features that improve code clarity and organization. While Enum allows you to define a fixed set of constants with type safety, EnumSet offers a high-performance Set implementation for those enum types, granting all the flexibility of the Collection framework. Understanding when and how to use each will greatly enhance your Java programming toolkit.