What does EnumSet really mean?

java object enums enumset
Adam picture Adam · Aug 6, 2012 · Viewed 61.8k times · Source

I have the following example:

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

public class SizeSet {

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


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

}

In this code I can understand that the Enum creates an Enum type of Sizes.

My question is: is largeSize an object of EnumSet type? What does it really mean? I really want to understand it better.

Answer

JB Nizet picture JB Nizet · Aug 6, 2012

As for any variable, its type is found in its declaration:

EnumSet largeSize

So yes, largeSize (which should be named largeSizes since it's a collection) is of type EnumSet. It should also be generified, and thus be declared as 

EnumSet<Size> largeSizes

What it means, is that largeSizes is of type EnumSet. An EnumSet is a Set which contains enum instance of a specific enum type, in a more efficient way than other Set implementations (like HashSet, TreeSet, etc.). To know what an EnumSet is, read its API.

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