Re: Set and .equals() semantics

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 09 May 2008 06:24:35 -0700

Message-ID:

<Bu6dnaMAE5EIzbnVnZ2dnUVZ_jCdnZ2d@earthlink.com>

Rex Mottram wrote:

Lew wrote:

I don't see how canonicalized objects in a Set would help anything.
AIUI, the OP wants to avoid some sort of overhead with retrieval of
"heavyweight" objects. But with a Set.find(), one would need to
create the second heavyweight object to find() the first - what is the
benefit? You create the same number of heavyweight objects anyway.

For the record, the benefit is in the area of storage (disk space), not
creation. Yes, I still have to create just as many H objects but most of
them end up being temporary and never reach any form of persistent storage.

RM

In the car model world, I think the distinction that may be missing is
between model identification and model details. I don't carry a shop
manual around in my car. When it needs fixing, I go to a service
station, tell them "1999 Nissan Quest" and they use that model
identification data to retrieve the detailed data.

I think I would model that by having a ModelId class that has small,
relatively simple objects, and each Car instance has a reference to its
own ModelId. Two ModelId objects are equal if they identify the same
model. There would also be a Map<ModelId,ModelDetails>.

Patricia