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

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:

// 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:

// 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:

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