VB.Net - Hashtable

The Hashtable class represents a collection of key-and-value pairs that are organized based on the hash code of the key. It uses the key to access the elements in the collection.

A hashtable is used when you need to access elements by using key, and you can identify a useful key value. Each item in the hashtable has a key/value pair. The key is used to access the items in the collection.

Properties and Methods of the Hashtable Class

The following table lists some of the commonly used properties of the Hashtable class −

Sr.No.	Property & Description
1	Count Gets the number of key-and-value pairs contained in the Hashtable.
2	IsFixedSize Gets a value indicating whether the Hashtable has a fixed size.
3	IsReadOnly Gets a value indicating whether the Hashtable is read-only.
4	Item Gets or sets the value associated with the specified key.
5	Keys Gets an ICollection containing the keys in the Hashtable.
6	Values Gets an ICollection containing the values in the Hashtable.

The following table lists some of the commonly used methods of the Hashtable class −

Sr.No.	Method Name & Purpose
1	Public Overridable Sub Add (key As Object, value As Object ) Adds an element with the specified key and value into the Hashtable.
2	Public Overridable Sub Clear Removes all elements from the Hashtable.
3	Public Overridable Function ContainsKey (key As Object) As Boolean Determines whether the Hashtable contains a specific key.
4	Public Overridable Function ContainsValue (value As Object) As Boolean Determines whether the Hashtable contains a specific value.
5	Public Overridable Sub Remove (key As Object) Removes the element with the specified key from the Hashtable.

Example

The following example demonstrates the concept −

Module collections
   Sub Main()
      Dim ht As Hashtable = New Hashtable()
      Dim k As String
      ht.Add("001", "Zara Ali")
      ht.Add("002", "Abida Rehman")
      ht.Add("003", "Joe Holzner")
      ht.Add("004", "Mausam Benazir Nur")
      ht.Add("005", "M. Amlan")
      ht.Add("006", "M. Arif")
      ht.Add("007", "Ritesh Saikia")
      
      If (ht.ContainsValue("Nuha Ali")) Then
         Console.WriteLine("This student name is already in the list")
      Else
          ht.Add("008", "Nuha Ali")
      End If
      ' Get a collection of the keys. 
      Dim key As ICollection = ht.Keys
      
      For Each k In key
         Console.WriteLine(" {0} : {1}", k, ht(k))
      Next k
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

006: M. Arif
007: Ritesh Saikia
008: Nuha Ali
003: Joe Holzner
002: Abida Rehman
004: Mausam Banazir Nur
001: Zara Ali
005: M. Amlan

vb.net_collections.htm

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