From MSDN site ,best example of HashTable

public static void Main()
        {
            // Create a new hash table.
            //
            Hashtable openWith = new Hashtable();

            // Add some elements to the hash table. There are no
            // duplicate keys, but some of the values are duplicates.
            openWith.Add("txt", "notepad.exe");
            openWith.Add("bmp", "paint.exe");
            openWith.Add("dib", "paint.exe");
            openWith.Add("rtf", "wordpad.exe");
            openWith["giri"] = "giriword.exe";

            IDictionaryEnumerator ide = openWith.GetEnumerator();
            while (ide.MoveNext())
                Console.WriteLine(ide.Key + " is related with " + ide.Value);

            ICollection ic = openWith.Keys;
            foreach (string item in ic)
            {
                Console.WriteLine(openWith[item]);
            }

            //// The Add method throws an exception if the new key is
            //// already in the hash table.
            //try
            //{
            //    openWith.Add("txt", "winword.exe");
            //}
            //catch
            //{
            //    Console.WriteLine("An element with Key = \"txt\" already exists.");
            //}

            //// The Item property is the default property, so you
            //// can omit its name when accessing elements.
            //Console.WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]);

            //// The default Item property can be used to change the value
            //// associated with a key.
            //openWith["rtf"] = "winword.exe";
            //Console.WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]);

            //// If a key does not exist, setting the default Item property
            //// for that key adds a new key/value pair.
            //openWith["doc"] = "winword.exe";

            //// ContainsKey can be used to test keys before inserting
            //// them.
            //if (!openWith.ContainsKey("ht"))
            //{
            //    openWith.Add("ht", "hypertrm.exe");
            //    Console.WriteLine("Value added for key = \"ht\": {0}", openWith["ht"]);
            //}

            //// When you use foreach to enumerate hash table elements,
            //// the elements are retrieved as KeyValuePair objects.
            //Console.WriteLine();
            //foreach (DictionaryEntry de in openWith)
            //{
            //    Console.WriteLine("Key = {0}, Value = {1}", de.Key, de.Value);
            //}

            //// To get the values alone, use the Values property.
            //ICollection valueColl = openWith.Values;

            //// The elements of the ValueCollection are strongly typed
            //// with the type that was specified for hash table values.
            //Console.WriteLine();
            //foreach (string s in valueColl)
            //{
            //    Console.WriteLine("Value = {0}", s);
            //}

            //// To get the keys alone, use the Keys property.
            //ICollection keyColl = openWith.Keys;

            //// The elements of the KeyCollection are strongly typed
            //// with the type that was specified for hash table keys.
            //Console.WriteLine();
            //foreach (string s in keyColl)
            //{
            //    Console.WriteLine("Key = {0}", s);
            //}

            //// Use the Remove method to remove a key/value pair.
            //Console.WriteLine("\nRemove(\"doc\")");
            //openWith.Remove("doc");

            //if (!openWith.ContainsKey("doc"))
            //{
            //    Console.WriteLine("Key \"doc\" is not found.");
            //}
            Console.ReadKey();
        }