Type of hashtable...

Question

I want to create a hash table having following schema:
for a given tableSize, it creates array of Object class of length tableSize. Every Object in array is actually Vector, to implement binary tree.
here is sample code:
public static class Room extends Object{
        Vector _node = new Vector(); //every room contains a vector, for binary tree implementation
        public Room(){
        public int insert(int element){
        int index=0;
        //code here
        return index;
        //gets and sets here...
}Here how i create this array:
int tableSize = 7;
Room[] hashTable= new Room[tableSize];
int nodeNumber = hashTable[integerToInsert%tableSize].insert(integerToInsert);Problem is, the last line gives NullPointerException :(
What am I doing wrong? I feel a stupid mistake...

Answer 1

I am not reinventing hash table, but creating some "mutant" on purpose. I need to stay Vector and Room class. However, Room class can inherit whatever, but it must support
Room[] hashTable= new Room[tableSize];Moreover, I don't want to use any ready classes like java.util.Map, because with all types of key-value problems, collusions want to deal for myself.