How to get number of possible items of an Enum?

Question

Is there a builtin way to get the number of items of an Enum with something like Myenum.length,

Or do I have to implement myself a function int size() hardcording the number of element?

Solution 1

Yes you can use the Enum.values() method to get an array of Enum values then use the length property.

public class Main {
    enum WORKDAYS { Monday, Tuesday, Wednesday, Thursday, Friday; }

    public static void main(String[] args) {
        System.out.println(WORKDAYS.values().length);
        // prints 5
    }
}

http://ideone.com/zMB6pG

Solution 2

You can get the length by using Myenum.values().length

The Enum.values() returns an array of all the enum constants. You can use the length variable of this array to get the number of enum constants.

Assuming you have the following enum:

public enum Color
{
    BLACK,WHITE,BLUE,GREEN,RED
}

The following statement will assign 5 to size:

int size = Color.values().length;

Solution 3

The enum.values() method is added by the Java complier and is not mentioned in the APIs.

Where is the documentation for the values() method of Enum?

Solution 4

To avoid calling values() method each time:

public class EnumTest {

    enum WORKDAYS {
       Monday,
       Tuesday,
       Wednesday,
       Thursday,
       Friday;

       public static final int size;
       static {
          size = values().length;
       }
   }


   public static void main(String[] args) {
      System.out.println(WORKDAYS.size); // 5
   }
}

Solution 5

MyEnum.values() returns the enum constants as an array.

So you can use:

int size = MyEnum.values().length

View more solutions

Comments

[Cyrille Ka]

length is not a method of an array, it is a property field, so you'd use it without parentheses.

[Rahul Bobhate]

@CyrilleKa: Thanks for notifying. Corrected it. :)

[Mark Jeronimus]

Enum.values() allocates a new array every time so it's not recommended for high call rate (i.e. for-loop condition). Cache the value if you need to call it very often.

[Hatefiend]

@MarkJeronimus Even without calling it often, this is still bad practice. Allocating an array just for the length property is silly, even if only done once.

[Bouh]

@Hatefiend so what do you suggest?

[Mahozad]

See this Kotlin issue aiming to replace Enum.values() with a more modern and performant alternative.