getting key using value

[vk02720]

Is there any way to retrieve the key using the value from
HashMap/Properties ?
containsValue(key) just returns true/false and not the actual key or
entry.
I have pairs of one-to-one mappings that I have to use both ways. What
data structure can be used ?

 

[Purush Rudrakshala]

You can use Jakarta commons collections BidiMap or you can maintain
two HashMaps, one with key as key, and another with value as key.

For more info on commons collections, see :
http://jakarta.apache.org/commons/collections/

 

[Thomas Weidenfeller]

Is there any way to retrieve the key using the value from
HashMap/Properties ?
containsValue(key) just returns true/false and not the actual key
or
entry.

I guess you mean containsValue(value). And no, there is no such beast
which delivers all keys (note the plural) for a particular value. You
have to iterate over the set of entries and check the values of all the
entries to find the keys.

I have pairs of one-to-one mappings that I have to use both ways. What
data structure can be used ?

For a quick hack two maps. One mapping A -> B and the other on for the
reverse lookup B -> A. Both maps wrapped in a class which has to ensure
consistency (both maps have to be updated at the same time).

/Thomas