C# | Check whether a Hashtable contains a specific key or not

Hashtable.Contains(Object) Method is used to check whether the Hashtable contains a specific key or not. Syntax:

public virtual bool Contains (object key);

Here, key is the Key of Object type which is to be located in the Hashtable. Return Value: This method returns true if the Hashtable contains an element with the specified key otherwise returns false. Exception: This method will give ArgumentNullException if the key is null. Note:

• Hashtable.ContainsKey(Object) Method is also used to check whether the Hashtable contains a specific key or not. This method behaves same as Contains() method.
• Contains method implements IDictionary.Contains. It behaves exactly as ContainsKey and this method is an O(1) operation.

Below programs illustrate the use of above-discussed method: Example 1: Output:

True

Example 2:

Runtime Error:

Unhandled Exception: System.ArgumentNullException: Key cannot be null. Parameter name: key

Reference:

• https://learn.microsoft.com/en-us/dotnet/api/system.collections.hashtable.contains?view=netframework-4.7.2