Difference Between Data Dictionary and HashTable

Data Dictionary and Hash Table both are used to collect data as Key/Value pair. We can differentiate both based on following criteria

1.    Generic

2.    Performance

3.    Thread

Generic:

Dictionary is a Generic Type but Hash Table is not Generic Type

Note: Generic Type is a type which is used to hold the value and Reference types. As we know there are two fundamental categories of types.

1.    value types (example: structures, primitive type, enums)

2.    Reference types (example: Classes, interface, arrays, strings etc..,)

Performance

Data Dictionary  is faster because there is no boxing/unboxing. And Hash table  is slow because - Hash table uses Object to hold things  .So you have to take care of type safety and cast it to appropriate data type when you take it out.

Hash Table have to box and unbox object which may consume memory that will affect performance.

Thread Safety

Dictionary is Type safety because we can’t insert random object into it. And we need not to cast value

Example:  Hash Table

    Hashtable objHashTable = new Hashtable();

    objHashTable.Add(200, 100);    // int

    objHashTable.Add(8.3 9, 200); // float

    objHashTable.Add('C', 300);  // char

    objHashTable.Add("7", 400);  // string

    mylblDisplay1.Text = objHashTable[200].ToString();

    mylblDisplay2.Text = objHashTable[8.3 9].ToString();

    mylblDisplay3.Text = objHashTable['C'].ToString();

    mylblDisplay4.Text = objHashTable["7"].ToString();

Example:  DataDictionary

Dictionary<string, int> dictionary = new Dictionary<string, int>();     dictionary.Add("cat", 2);     dictionary.Add("dog", 1);     dictionary.Add("llama", 0);     dictionary.Add("iguana", -1);   // ----------- Not Possible for HashTable ----------       //dictionary.Add(1, -2); // Compilation Error       foreach (KeyValuePair<string, int> pair in dictionary)     {         lblDisplay.Text = pair.Value + " " + lblDisplay.Text;     }

Important Notes:

·        We cannot use dictionary (generics) with web services. The reason is no web service