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

Last Updated : 01 Feb, 2019

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:

CSharp

// C# code to check whether the Hashtable
// contains a specific key or not
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a Hashtable
        Hashtable myTable = new Hashtable();

        // Adding elements in Hashtable
        myTable.Add("g", "geeks");
        myTable.Add("c", "c++");
        myTable.Add("d", "data structures");
        myTable.Add("q", "quiz");

        // Checking if Hashtable contains
        // the key "Brazil"
        Console.WriteLine(myTable.Contains("d"));
    }
}

Output:

True

Example 2:

CSharp

// C# code to check whether the Hashtable
// contains a specific key or not
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a Hashtable
        Hashtable myTable = new Hashtable();

        // Adding elements in Hashtable
        myTable.Add("1", "C");
        myTable.Add("2", "C++");
        myTable.Add("3", "Java");
        myTable.Add("4", "Python");

        // Checking if Hashtable contains
        // the key null. It will give exception
        // ArgumentNullException
        Console.WriteLine(myTable.Contains(null));
    }
}