Java array of Hashtables

Question

I need an array of Hashtables in a program that is storing all words from a given set of documents.

Index 1 of the array holds a hashtable of String -> Double which stores a word, and its count for document 1 (array index 100 = document number 100's hashtable).

I dont need help using this data structure, just in creating it. I declare the Hashtable Array as follows:

Hashtable<String,Double>[] h1 = new Hashtable<String,Double>[];

... but this does not compile.

(NOTE: The Double is necessary rather than an Integer in the above declaration for later usage.)

QUESTION: How do you create an array of hashtables which stores String->Double ???

Any suggestions appreciated guys....

Answer 1

... but this does not compile.

That's because the array has no name, new expects a number of elements and you can't just allocate an array of generics. Prefer a List instead:

List<Hashtable<String,Double>> wordCountPerDoc
  = new ArrayList<Hashtable<String,Double>>();

Answer 2

just use

    @SuppressWarnings("unchecked")
    Hashtable<String,Double>[] h = (Hashtable<String,Double>[])new Hashtable<?,?>[10];
    h[0] = new Hashtable<String, Double>();

Answer 3

why don't you use a Map<Integer, Map<String, Double> > ? this way you don't waste space for non-existing documents, and still get O(1) retrieval.