C# | Gets an ICollection containing the keys in the Hashtable

Last Updated : 11 Jul, 2025
Hashtable.Keys Property is used to get an ICollection containing the keys in the Hashtable. Syntax: 
public virtual System.Collections.ICollection Keys { get; }
Return Value: This property returns an ICollection containing the keys in the Hashtable. Note:
  • The order of keys in the ICollection is unspecified.
  • Retrieving the value of this property is an O(1) operation.
Below programs illustrate the use of above-discussed property: Example 1: CSharp 
// C# code to get an ICollection containing
// the keys in the Hashtable.
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("4", "Even");
        myTable.Add("9", "Odd");
        myTable.Add("5", "Odd and Prime");
        myTable.Add("2", "Even and Prime");

        // Get a collection of the keys.
        ICollection c = myTable.Keys;

        // Displaying the contents
        foreach(string str in c)
            Console.WriteLine(str + ": " + myTable[str]);
    }
}
Output: 
5: Odd and Prime
9: Odd
2: Even and Prime
4: Even
Example 2: CSharp 
// C# code to get an ICollection containing
// the keys in the Hashtable.
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("India", "Country");
        myTable.Add("Chandigarh", "City");
        myTable.Add("Mars", "Planet");
        myTable.Add("China", "Country");

        // Get a collection of the keys.
        ICollection c = myTable.Keys;

        // Displaying the contents
        foreach(string str in c)
            Console.WriteLine(str + ": " + myTable[str]);
    }
}
Output: 
Chandigarh: City
India: Country
China: Country
Mars: Planet
Reference:
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