Re: retrieve the key from a map

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 07 Sep 2006 13:21:15 GMT

Message-ID:

<f1VLg.7642$bM.6304@newsread4.news.pas.earthlink.net>

ralf@rw7.de wrote:

Hi everyone,

I want to retrieve a key from a map, and I don't find a way to do this.
For instance there is the following code:

HashMap m = new HashMap();
String key = new String("k");
m.put(key, "v");

Later I don't have any reference to "key" anymore, other than the
reference in the map. But I know, the string is "k". I want to retrieve
the instance that is the key in the map.

If you know the String is "k", you can find the specific key instance by
getting the keySet, and iterating over it checking for .equals equality
to "k".

If you do this frequently, keep a separate hash map that contains each
key in m as both key and value:

m_keys.put(key,key)

When you want to do the retrieval:

m_keys.get("k")

However, I have my doubts about a design that depends on overriding
..equals in a class, but does not treat instances that equal each other
as being equivalent. Note that two .equals equal instances cannot both
be keys in the map at the same time.

What are you really trying to achieve?

Patricia