Question

I want to create a table with String keyvalues and integer data. Right now I am leaning towards creating a two-dimensional HashMap:

HashMap<String, HashMap<String, Integer>>

Is that going to be my fastest and most flexible option? I am using it to create a language model so there will be a lot of changes and frequent lookups. Also, is that the correct syntax? And how would I initialize it?

new HashMap<String, new HashMap<String, Integer>> 

seems wrong to me for some reason but I can’t place why.

Answer 1

You could also define your map like this:

map = new HashMap<Pair<String>,Integer>();

Where Pair has a reasonable definition (don’t forget equals and hashCode!).

This is simpler (insert doesn’t have to check whether the sub-map is created or not) and probably faster (only 1 hash lookup instead of 2).

If you know of some character that can’t be in either of your strings, then you could just use String instead of Pair<String> where the key is the concatenation of the two keys with that character as a separator.