C# | Get an enumerator that iterates through the Hashtable

Hashtable.GetEnumerator Method is used to returns an IDictionaryEnumerator that iterates through the Hashtable.

Syntax:

public virtual System.Collections.IDictionaryEnumerator GetEnumerator ();

Return Value: It returns an IDictionaryEnumerator for the Hashtable.

Below programs illustrate the use of Hashtable.GetEnumerator Method:

Example 1:

// C# code to get an IDictionaryEnumerator
// that iterates through the Hashtable
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a Hashtable named myhash
        Hashtable myhash = new Hashtable();

        // Adding key/value pairs in myhash
        myhash.Add("A", "Apple");
        myhash.Add("B", "Banana");
        myhash.Add("C", "Cat");
        myhash.Add("D", "Dog");
        myhash.Add("E", "Elephant");
        myhash.Add("F", "Fish");

        // To get an IDictionaryEnumerator
        // for the Hashtable.
        IDictionaryEnumerator myEnumerator = myhash.GetEnumerator();

        // If MoveNext passes the end of the
        // collection, the enumerator is positioned
        // after the last element in the collection
        // and MoveNext returns false.
        while (myEnumerator.MoveNext())
            Console.WriteLine(myEnumerator.Key + " --> "
                              + myEnumerator.Value);
    }
}

Output:

B --> Banana
C --> Cat
A --> Apple
F --> Fish
D --> Dog
E --> Elephant

Example 2:

// C# code to get an IDictionaryEnumerator
// that iterates through the Hashtable
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a Hashtable named myhash
        Hashtable myhash = new Hashtable();

        // Adding key/value pairs in myhash
        myhash.Add("I", "first");
        myhash.Add("II", "second");
        myhash.Add("III", "third");
        myhash.Add("IV", "fourth");
        myhash.Add("V", "fifth");

        // To get an IDictionaryEnumerator
        // for the Hashtable.
        IDictionaryEnumerator myEnumerator = myhash.GetEnumerator();

        // If MoveNext passes the end of the
        // collection, the enumerator is positioned
        // after the last element in the collection
        // and MoveNext returns false.
        while (myEnumerator.MoveNext())
            Console.WriteLine(myEnumerator.Key + " --> "
                              + myEnumerator.Value);
    }
}

Output:

III --> third
IV --> fourth
V --> fifth
II --> second
I --> first

Note:

• The foreach statement of the C# language hides the complexity of the enumerators. Therefore, using foreach is recommended, instead of directly manipulating the enumerator.
• Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.
• Current returns the same object until either MoveNext or Reset is called. MoveNext sets Current to the next element.
• An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and its behavior is undefined.
• This method is an O(1) operation.

Reference:

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