What is EnumSet in Java and How Does It Work?

What does EnumSet really mean in Java?

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

public class SizeSet {
    public static void main(String[] args) {
        EnumSet<Size> largeSize = EnumSet.of(Size.XL, Size.XXL, Size.XXXL);
        for (Iterator<Size> it = largeSize.iterator(); it.hasNext(); ) {
            Size size = it.next();
            System.out.println(size);
        }
    }
}

enum Size {
  S, M, L, XL, XXL, XXXL;
}

EnumSet is a specialized Set implementation for use with enum types in Java. It is very efficient and provides a way to work with groups of enum constants.

// Create an EnumSet containing all sizes
EnumSet<Size> allSizes = EnumSet.allOf(Size.class);
System.out.println(allSizes); // Output: [S, M, L, XL, XXL, XXXL]

Causes

• EnumSet allows you to create a set of enum constants where you can perform set operations like union, intersection, and difference.
• EnumSet is implemented as a bit vector, making it highly space-efficient compared to other Set implementations.

Solutions

• You can create an EnumSet using the static method EnumSet.of() to include specific enum constants.
• Use EnumSet.allOf() to create a set containing all the constants of a specified enum type.

Mistake: Incorrect type parameter in EnumSet declaration (using raw type).

Solution: Always parameterize your EnumSet with the enum type, e.g., EnumSet<Size>.

Mistake: Not checking if common methods of Set like contains(), add(), or remove() apply to EnumSet incorrectly.

Solution: Refer to the EnumSet documentation for supported operations. Use add() and remove() for mutable EnumSets.