What does EnumSet really mean?

Question

I have the following example:

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

public class SizeSet {

    public static void main(String[] args) {
             


        

Answer 1

Simplifying your code

EnumSet largeSize = EnumSet.of(Size.XXXL, Size.XXL, Size.XL, Size.L);
for(Size size: largeSize)
    System.out.print(size+" ");

You can see that largeSize is a regular Set except its designed to store Enums. How is that different? Firstly the JVM knows all the possible values of the set which means instead of storing all the objects it can use a bitmap where 1 means the item is present and 0 means it is not. This also means the order of the set is the order of the ordinal values i.e. the order they were defined. This is why this prints

L XL XXL XXXL

If you want to know more detail I suggest you read the source for this class.