C# Hashtable Tutorial For Beginners With Examples

A C# Hashtable represents a collection in which objects are stored and retrieved using a key.

Each key in a Hashtable has a hash code using which the objects in a Hashtable are organized.

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Create a Hashtable in C#

A Hashtable can be created using the below code:

    Hashtable shoppingCart = new Hashtable();

Add items to a C# Hashtable

To add items to a Hashtable Add method is used. In the below example a key called as Camera with value 3 is added to the Hashtable shoppingCart.

     shoppingCart.Add("Camera", 3);     
        

	Every item in a Hashtable has a unique key and an associated value. A Hashtable is a collection of such key/value pairs. Each of these items is a type of DictionaryEntry object.

Below three unique keys are added to a Hashtable. The key name and the associated value is then displayed using a foreach loop.

    Hashtable shoppingCart = new Hashtable();

    shoppingCart.Add("Camera", 3);
    shoppingCart.Add("Computer", 2);
    shoppingCart.Add("Trouser", 5);

    foreach (DictionaryEntry item in shoppingCart)
    {
        Console.WriteLine("Key " + item.Key + " has value " + item.Value);
    }
        

Output:
Key Computer has value 2
Key Trouser has value 5
Key Camera has value 3

	Objects in a Hashtable can be null whereas the keys can't be.

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Remove items from C# Hashtable

To remove items from a Hashtable Remove method is used. In the below example the keyCamera is removed from the Hashtable shoppingCart.

     shoppingCart.Remove("Camera", 3);     
        

	Removing a key also removes the associated value from a Hashtable.

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Methods and Properties of a C# Hashtable

Commonly used methods of a Hashtable are:

Method	Description
Add	Adds an item with a specific key and value to the Hashtable.
Clear	Removes all items from the Hashtable.
ContainKey	Checks if a specific key is present in a Hashtable.
ContainsValue	Checks if a specific value is present in a Hashtable.
GetHash	Gets the hash code associated with a key in a Hashtable.
Remove	Removes a key and associated value from a Hashtable.

Commonly used properties of a Hashtable are:

Property	Description
Count	Returns the number of items (Key/Value pairs) present in a Hashtable.
IsReadOnly	Returns a boolean value which specifies whether a Hashtable is readonly or not.
Item	Represents a key/value pair in a Hashtable.
Keys	Returns a collection of all the keys present in a Hashtable.
Values	Returns a collection of all the values present in a Hashtable.