Question

Attempting to better understand chaining on a hashtable. Seeking a simple table that hashes a value and only associates one integer to the value hashed. Here is sample code of the problem in question…

      /* hash string value return int */
      public int hashFunction(String D) {
          char[] Thing = D.toCharArray();
          for(int i=0; i < Thing.length; i++){
             index += Thing[i]; }
          return index % TABLE_SIZE;          
      }

      /* hash string value return void */
      public void hashFunction(String D) {
        char[] Thing = D.toCharArray();
        for(int i=0; i < Thing.length; i++){
         index += Thing[i];}
        int hash = index % TABLE_SIZE;
        if(table[hash] == null){
          table[hash] = new HashEntry( Level,  Value );
        }        
        else{
          table[hash].setNext(nd);
        }
      }

      /* miscellaneous code snippet */
      if(table[hash] == null){
        table[hash] = new HashEntry();
      }

      else if (Data.compareTo("VAR") == 0) {
          Data = inFile.next();   
            char[] Thing = Data.toCharArray();
            for(int i=0; i < Thing.length; i++){
            hash += Thing[i];}
            hash = hash % TABLE_SIZE;           
            hm.setIntoHashTable(hash);      
                Data = inFile.next();
                    if(Data.compareTo("=") == 0) {
                    Data = inFile.next();
                    int value = Integer.parseInt(Data);
                    hm.getIntoHashTable(he.setValue(value));
                }
      }

Answer 1

Well the chaining occurs when you have collision in the indexes.

Lets assume you have a TABLE_SIZE=10

Now you have to store string abc, so you get hash as 4

Now when you gonna store string cba, you end up with same hash 4

So now to store cba at the same index, you will create and store a List at index 4.

The List will contain both abc and bca. This List is called chain and this process of storing multiple values at the same hash is called Chaining.

Pseudo code look like:

if(table[hash] == null)
  table[hash] = new ArrayList<HashEntry>();//APPEND ON TO THE LOCATION ALREADY THERE!
table[hash].add(new HashEntry());

The table will be declared as:

@SuppressWarnings("unchecked")
List<HashEntry>[] table = new List[TABLE_SIZE];

You might have to suppress warning as arrays and generics dont go smoothly.