Re: Can I compare references (in a sense of compareTo method)?

From:

Knute Johnson <nospam@rabbitbrush.frazmtn.com>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 20 Sep 2007 14:43:52 -0700

Message-ID:

<sQBIi.249$sS6.197@newsfe14.lga>

chucky wrote:

When testing two objects for equality (with == operator), the
references are compared. But it is not allowed to compare the objects
(references) with <, <=, >, >= operators.

Is it possible somehow to get the address of an object and then
compare it?

What I want to do is to have each instance of my class unique, so that
two objects are equal only if they are the same object. This is easy,
I can make equals method to compare references. But I would like to
use these objects in TreeSet/TreeMap and therefore implement the
compareTo method in a way that would be consistent with respect to
equals.

I can think of one workaround: the class having an additional integer
field id and creating the instances with a synchronized factory
method. But just want to know if it is possible without that extra
field.

Thanks for replies!

Tomas

Do you not have access to the docs? It has nothing to do with == or the
address of the object. You need to look at TreeMap and Comparator.

public class TreeMap<K,V>
extends AbstractMap<K,V>
implements NavigableMap<K,V>, Cloneable, Serializable

A Red-Black tree based NavigableMap implementation. The map is sorted
according to the natural ordering of its keys, or by a Comparator
provided at map creation time, depending on which constructor is used.

--

Knute Johnson
email s/nospam/knute/