This is a 3 part tutorial on the HashTable available in .NET 2.0. Part one is here and soon you will get access of  other two part might be some brain storming sessions in the last one. Please download the attached code to see the working sample. 

First of all Why HashTable? Answer is very simple. Suppose you have some data, which needs to be stored in two dimensional array and have a link format of Key and Value. For example, a person name and his social security number and we can access there data using a key.

A close friend of Hashtable is Array (came from C/C++), it is an instance of System.Array class, but to access data from array you must have an index and that is of int Type. And second you must specify the size of the Array at the time of instantiations.

Family contains

1. ArrayList
2. Collection
3. Dictionary ( Hashtable or Maps ).

Dictionaries or Hashtable

Are very sophisticated data structures that allows us to access an element based on some key, which can be of any type.

Hashtable in .net

1. Is member of System.Collections namespace.
2. Contains15 constructors ( wow, try them all) but you will mostly use.    

        Hashtable _table2 = new Hashtable(10); // capacity or size.
        Hashtable _table3 = new Hashtable(10, 06); //capacity , loadfactor

Loadfactor this factor helps a lot if you looking for performance, The smaller the load size (fracton of the tashtable full .6 measn 60% full) , the more efficiently our hash table works and the more memory it occupy.           

Now have some code

1. Create a Hashtable 
         

   Hashtable _simpleTable = new Hashtable();
   

2. Add some data in it.
       

        _simpleTable.Add("Key1", "Value1");
   

   _simpleTable.Add("Key2", "Value2");
   
3. Get the size.
   
   

   _simpleTable.Count; // an int value.
   

4.  Now to fetch data

• Create an object of IDictonaryEnumerator , this is an interface that creates an enumerator and customized for    Dictonary  objects.
      
  IDictionaryEnumerator _enumerator = _simpleTable.GetEnumerator();
  
• while (_enumerator.MoveNext())
  {
     _string += _enumerator.Key + " ";
     _string += _enumerator.Value + "\n";
  }
  
• and that all you fetched the Data !!!
  
• clear hash table.. 
  
  _simpleTable.Clear();
  
• Search for a specific key : remember its value type when used 
  
  

  if (_simpleTable.ContainsKey("Key1"))
  {
       Console.WriteLine("Key1 is present");
  }

• Search for a specific key : remember its value type when used
  
  

  if (_simpleTable.ContainsValue("Value1"))
  {
       Console.WriteLine("Value1 is present");
  }

•  Have all this done and you will get more stuff in the next post.
  

•  Try this and Cheers!!!!!