Hashtable

[Ronald Pruitt]

Can anyone show me how to build a hashtable to test for some string values to see how they would hash into a table. It's late and I may not be to asking this just right.I want to make a test hashtable, insert some words and see where they are put in the table. would like the size of the table to be 101, but everytime I try to call what I've done I get an error saying I can't use [] to find the position. I can give you what I have for code but it's far from finished I fear.

import java.util.*;
class Testit implements Elem
{
Elem R;
int next = 0;
Hashtable T;
int M;
public Testit(int initialCapacity)throws IllegalArgumentException
{
int M = 101;
}
public Testit()
{}
public void hashInsert(Elem R)
{ // Insert record R into table T
int home; // Home position for R
int pos = home = h(R.key()); // Initial position
for (int i = 1; T[pos] != null; i++)
{
pos = (home + p(R.key(), i)) % M;// Next probe slot
Assert.notFalse(T[pos].key() != R.key(), "Duplicates not allowed: ");
}
T[pos] = R; // insert R
}

public Elem hashSearch(int K) // Search for the record with key K
{
int home; // Home position K
int pos = home = h(K); // initial position
for (int i = 1; (T[pos] != null) && (T[pos].key() != K); i++)
pos = (home + p(K, i)) % M;// Next probe position
if (T[pos] == null) return null;// K not in has table
else return T[pos]; // Found it
}

  static long ELFhash(String key, int M)
{
long h = 0;
for (int i = 0; i < key.length(); i++)
{
h = (h << 4) + (int) key.charAt(i);
long g = h & 0xF0000000L;
if (g != 0) h ^= g >>> 24;
h &= ~g;
}
return h % M;
}

}

If you can be of any help I thank you.
Ron

[Frank Carver]

I guess you are more used to C++/STL than Java, as the program above has a lot of other conversion issues too. In Java, a variable is just a reference, so you always need to initialize them before use. T is declared as a reference to a Hashtable, for example, but nowhere does it say T = new Hashtable(), so T is always null. Likewise for M which is never initialized and so remains at 0 (it may look as if it is initialized in one of the constructors, but that actually just assigns a value to a local variable which is then discarded).

[Ronald Pruitt]

I want to thank you both, I am just getting started at this and I know there are a lot of problems with the code. Is there a way to write a hashtable without using Java's Hashtable class to solve the problem above?