问题
I stumbled upon multi_index on a lark last night while pounding my head against a collection that I need to access by 3 different key values, and also to have rebalancing array semantics. Well, I got one of my two wishes (3 different key values) in boost::multi_index.
Does anything similar exist in the Java world?
回答1:
I have just finished MultiIndexContainer in Java: http://code.google.com/p/multiindexcontainer/wiki/MainPage. I know that it is not complete equivalent of boost multi_index_container but maybe it could be sufficient for your requirement.
回答2:
Resurrecting an old question, but take a look at CQEngine as a solution.
For background also see related question How do you query object collections in Java (Criteria/SQL-like)?
回答3:
I think the short answer is no, there's no obvious equivalent.
The boost multi-index class is very heavily templated, which isn't easily translatable in Java. There are generics, but they're not at all the same. ( How are Java generics different from C++ templates? Why can't I use int as a parameter? ).
So without templating, what would the multi-index class look like?
I imagine you would have your data class, e.g. Person, containing index members like a Map implementation. At this point, you have a choices:
- Add some "indexes" directly to the Person class (like some Hashtables) and write lookup functions. Manage index synchronization within the Person class.
- Write an "IndexProvider" class that decouples the index functionality entirely from Person - it would have to be able to dynamically create different index types and I would imagine you would handle synchronization via callbacks.
- Some mix of 1) and 2) - like an abstract base class for index functionality, which doesn't properly decouple the behaviour but does provide some code reuse.
I think, in the majority of cases 1) is the easiest to write, easiest to maintain and is probably the most performant. 2) seems like over-engineering.
The other option, if you have a lot of data structures that need indexing, is to store them in a database.
回答4:
I think you can find for the answer in google guava library. Probably multimaps solve your needs.
https://code.google.com/p/guava-libraries/wiki/CollectionUtilitiesExplained
As commented in these threads:
- Java - How to separate a list based on a property of it's elements
- Multilevel map in Java
回答5:
I have no idea what boost::multi_index means, but based on the rest of your question, I think you might be talking about a multi key map
来源：https://stackoverflow.com/questions/3070598/is-there-an-equivalent-of-boostmulti-index-for-java-someplace