Re: Indexing by multiple keys

From:

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 02 Aug 2009 22:54:38 -0400

Message-ID:

<4a76516b$0$303$14726298@news.sunsite.dk>

Donkey Hottie wrote:

"Arne Vajh?j" <arne@vajhoej.dk> wrote in message
news:4a74495d$0$301$14726298@news.sunsite.dk

rossum wrote:

On Fri, 31 Jul 2009 14:35:56 -0700 (PDT),
"nooneinparticular314159@yahoo.com"
<nooneinparticular314159@yahoo.com> wrote:

I would like to use an object that behaves like a
hashmap (ie. put, get, with a key), but I'd like to be
able to index items in that object by more than one key.

Is there a way to do this?

Ie. if I had a name for the objects I'm adding as well
as a social security number, I'd like to be able to
return the object by either name or number depending on
need. Is there an object that does this, or do I have
to write it myself?

As an alternative you could use a database. Set up a
table with Name, SSN, etc. and build indexes for the
Name and SSN fields for fast retrieval.

In most cases apps have both a persistent and an in memory
representation.

Even with correct index a database does not exactly have
the same performance characteristics as a HashMap.

Given the HashMap contains the population of U.S. and the use case needs
one search from that popula, a HashMap that needs to be loaded before
the search does not have the performance characters of an SQL SELECT
with the key.

True.

But having then entire US population and only needing to lookup
one person is a rather unlikely scenario.

Arne