TreeSet of enum not sorted

[Mark Lund]

This seems pretty basic but can't figure out why the enums appear to be unsorted in the second TreeSet. Am studying SCJP and don't feel real strong here so please give me some pointers. I can't override compareTo or equals and hashCode for that matter. This is not from any book. Mark

import java.util.*;

class TestCollect{

enum Children{
Michelle,
Lisa,
Sarina,
Brenda;
}

public static void main(String [] argv){
Set <String> set= new TreeSet<String>();
set.add(Children.Michelle.toString());
set.add(Children.Lisa.toString());
set.add(Children.Sarina.toString());
set.add(Children.Brenda.toString());
for (String i:set)
System.out.println(""+i);

Set <Children> set2= new TreeSet<Children>();
set2.add(Children.Michelle);
set2.add(Children.Lisa);
set2.add(Children.Sarina);
set2.add(Children.Brenda);
for (Children i:set2)
System.out.println(i.name());
}
}

[Keith Lynn]

Note that Enum<E> implements Comparable<E>, and the compareTo method is final so you can't override it.

The output of the program implies that the natural ordering of an enum type is the order in which you declare the constants.

[Jim Yingst]

Adding to Keith's post: the API for Enum's compareTo() method states explicitly the same thing the output implies. If you want a different ordering (alphabetical perhaps?), you need to create a Comparator and use one of the TreeSet constructors which accepts a Comparator.

[Mark Lund]

Thanks guys. You've been very helpful! Mark