Can I have a key-key map (as opposed to key-value) in Java?

Question

What if I need to quickly search not only by the key but also by value. In other words, is there a construction like key-key as opposed to key-value?

Answer 1

Sounds like you want a bimap - I'd use the implementations in Guava if I were you; there's a BiMap interface, and various implementations such as HashBiMap and ImmutableBiMap.

Note that you generally view a BiMap from one "side" (K1 to K2), and just call inverse() to get the opposite view of things (K2 to K1).

Answer 2

Several libraries have something like that. For example, Google Guava has a BiMap (bidirectional map). Unfortunately there's no bidirectional map in the standard Java library.