Enums in Treeset

[Abhi vijay]

   import java.util.*;
enum Days
{
	MONDAY(4),
		TUESDAY(2)

		,SUNDAY(3);

	Days(int d)
	{
		this.d=d;
		System.out.println("CONSTRUCTOR");
	}

	int d;
}

public class Enum_Treeset
{
	public static void main(String[] args)
	{

		TreeSet<Days> s =new TreeSet<Days>();
		s.add(Days.MONDAY);
		s.add(Days.TUESDAY);
		s.add(Days.SUNDAY);

		System.out.println(s);
	}
} 

here how is the sorting done?

[Ruben Soto]

TreeSet will use the natural ordering of the elements in this case (since you are not passing a Comparator to the TreeSet constructor.) And I think the natural ordering of enums is the order in which the enum constants are declared in the body of the enum. You could try and change the order of declaration in the enum and run it again to confirm.

[Balaji Bang]

Yes I tried this. it is getting the order in which enums are declared in the enum body.

[Abhi vijay]

Yes. same here. We shall wait for Punit or Ankit to confirm.

[James Tharakan]

Abhi vijay wrote: We shall wait for Punit or Ankit to confirm.

why?

[Rafael Angarita]

compareTo

public final int compareTo(E o)

Compares this enum with the specified object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object. Enum constants are only comparable to other enum constants of the same enum type. The natural order implemented by this method is the order in which the constants are declared.

Specified by:
compareTo in interface Comparable<E extends Enum<E>>

Parameters:
o - the object to be compared.
Returns:
a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

From: http://java.sun.com/javase/6/docs/api/java/lang/Enum.html