Re: TreeMap question

From:

"Mike Schilling" <mscottschilling@hotmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 22 Dec 2010 19:19:28 -0800

Message-ID:

<ieuf3o$sno$1@news.eternal-september.org>

"Lew" <noone@lewscanon.com> wrote in message
news:ieu9mf$pmt$1@news.albasani.net...

laredotornado wrote:

I'm using Java 1.6. I have a TreeMap that maps Integer to objects.
Given an integer that is given to be a key in this map, how can I
figure out what the key is immediately before the given one? Let me
know if this question doesn't make sense, - Dave

Patricia Shanahan wrote:

Use your TreeMap's lowerKey(K) method.

More generally, use the API documentation for Java 1.6. If you use an
older version of the documentation, you will miss out on some handy
java.util features.

Corollary point: This is a use case for a more specific type declaration
than 'Map'.

And demonstrates an interesting feature of Java class evolution.
lowerKey(K) is in all existing concrete implementations of SortedMap, and
(it seems to me) would be useful and straightforward to implement in any
reasonable implementation. But because it's not possible to add a method to
an interface while keeping compatibility, lowerKey(K) was not added to
SortedMap itself.