The contract for compareTo is here with the Comparable interface
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Comparable.html

Essentially compareTo expresses the order of two things (anything that
declares it has an order--e.g. is Comparable) by returning a negative value
if the first precedes the second, a positive value if the second precedes
the first and 0 if they are equal. You can make up an ordering for any kind
of object you like.  I also strongly recommend that the equals method be
compatible with compareTo--I've been tripped up when they're not. There's no
requirement that the magnitude of compareTo yield the distance between the
items.

The real question here is how to define the ordering function and that
depends entirely on what's in the object.  For example, if an object has
   String lastname
   String firstname
   int age

you can write an ordering function that goes age, lastname, firstname like
this so that it compares the various fields in order of importance.  If the
fields are different, stop and return an answer.  If they're the same
(yields 0), go test the next field.

public int compareTo (Object o) {
 MyObject myObject = (MyObject)o;
 if (age < o.getAge()) return -1;
 if (age > o.getAge ()) return 1;

 int c = lastname.trim().toLowerCase().compareTo
(o.getLastName().trim().toLowerCase());
 if (c != 0) return c;

 return
firstname.trim().toLowerCase.compareTo(o.getFirstName().trim().toLowerCase());

Matt Humphrey http://www.iviz.com/