Path: csiph.com!usenet.pasdenom.info!news.albasani.net!eternal-september.org!feeder.eternal-september.org!mx04.eternal-september.org!.POSTED!not-for-mail From: Jim Janney Newsgroups: comp.lang.java.programmer Subject: Re: Glitch in Java Collections (No descendingMap in LinkedHashMap) Date: Wed, 10 Oct 2012 10:28:29 -0600 Organization: nose and toes the same way goes Lines: 23 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: mx04.eternal-september.org; posting-host="75975abe3fe3503ca7350803ab98e478"; logging-data="3709"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/L8drGROVMwyFkvXVZKOyK" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux) Cancel-Lock: sha1:phPvKhVH/tVEnZ7lwR613QcnJDU= sha1:BM7HfNejC09vZ3zK9inrBApWAto= Xref: csiph.com comp.lang.java.programmer:19227 Eric Sosman writes: > On 10/10/2012 11:00 AM, Jim Janney wrote: >> Jim Janney writes: >> >>> Jan Burse writes: >>> [...] >>> If I really needed that functionality I'd probably try maintaining my >>> own access-order list in parallel to the map. >> >> Oops, stupid me. The other way is to define a comparator based on >> insertion order, and then use a SortedMap. > > Defining the comparator might be something of a struggle, > especially if the same object instance could be referred to by > two different LinkedHashMaps. The trick is finding a way to link the ordering information (probably a counter assocated with the map) with the keys themselves. This is the kind of problem where IdentityHashMap comes in handy. -- Jim Janney