I’m looking for the most basic solution to create multiple indexes on a Java Collection.
Required functionality:
- When a Value is removed, all index entries associated with that value must be removed.
- Index lookup must be faster than linear search (at least as fast as a TreeMap).
Side conditions:
- No dependencies on large (like Lucene) libraries. No uncommon or not well tested libraries. No database.
- A library like Apache Commons Collections etc. would be ok.
- Even better, if it works with JavaSE (6.0) alone.
- Edit: No self-implemented solution (thanks for the answers suggesting this – it’s good to have them here for completeness, but I already have a solution very similar to Jay’s) Whenever several people find out, that they implemented the same thing, this should be part of some common library.
Of course, I could write a class that manages multiple Maps myself (that’s not hard, but it feels like reinventing the wheel). So I’d like to know, if it can be done without – while still getting a simple usage similar to using a single indexed java.util.Map.
Thanks, Chris
Update
It looks very much as if we haven’t found anything. I like all your answers – the self developed versions, the links to database-like libraries.
Here’s what I really want: To have the functionality in (a) Apache Commons Collections or (b) in Google Collections/Guava. Or maybe a very good alternative.
Do other people miss this functionality in these libraries, too? They do provide all sorts of things like MultiMaps, MulitKeyMaps, BidiMaps, … I feel, it would fit in those libraries nicely – it could be called MultiIndexMap. What do you think?
Each index will basically be a separate
Map. You can (and probably should) abstract this behind a class that manages the searches, indexing, updates and removals for you. It wouldn’t be hard to do this fairly generically. But no, there’s no standard out of the box class for this although it can easily be built from the Java Collections classes.