Question

I just want to know if it is possible to create a hashtable in java of the form <key, hash table>.

Essentially the first key leads me to a new hash table; then I search that table using another key.

Answer 1

Sure it is:

Map<K1, Map<K2, V>> themap = new HashMap<K1, Map<K2, V>>();

where K1 is the key of the “hash table”, and K2 and V are the key and value type of the inner “hash table”.

edit: as @AndreiBodnarescu rightly points out, you must also choose your Map implementation carefully (Map is an interface). Ask yourself the following questions:

• is multithreading access required on the outer/inner map? If yes, consider Hashtable or Collections.synchronizedMap(...);
• does insertion order matter? If yes, consider LinkedHashMap;
• do you want keys to be sorted? If yes, consider TreeMap.

Choose your implementation carefully!