Java Hashmap: How to get key from value?

Question

If I have the value \"foo\", and a HashMap ftw for which ftw.containsValue(\"foo\") returns true, how can I

Answer 1

1. If you want to get key from value, its best to use bidimap (bi-directional maps) , you can get key from value in O(1) time.

   But, the drawback with this is you can only use unique keyset and valueset.

2. There is a data structure called Table in java, which is nothing but map of maps like

   Table< A, B , C > == map < A , map < B, C > >

   Here you can get map by querying T.row(a);, and you can also get map by querying T.column(b);

In your special case, insert C as some constant.

So, it like < a1, b1, 1 > < a2, b2 , 1 > , ...

So, if you find via T.row(a1) ---> returns map of --> get keyset this returned map.

If you need to find key value then, T.column(b2) --> returns map of --> get keyset of returned map.

Advantages over the previous case :

1. Can use multiple values.
2. More efficient when using large data sets.