Check if Hashtable has a fixed size in C#

The IsFixedSize property in C# is used to check whether a Hashtable has a fixed size or not. A fixed-size Hashtable does not allow adding or removing elements, but existing elements can still be modified. Regular Hashtables created using standard constructors are not fixed-size by default.

Syntax

Following is the syntax to check if a Hashtable has a fixed size −

bool isFixed = hashtable.IsFixedSize;

Return Value

The IsFixedSize property returns a bool value −

• True − If the Hashtable has a fixed size
• False − If the Hashtable can grow or shrink dynamically

Using IsFixedSize with Regular Hashtable

Example

using System;
using System.Collections;

public class Demo {
    public static void Main(){
        Hashtable hash = new Hashtable(10);
        hash.Add("1", "A");
        hash.Add("2", "B");
        hash.Add("3", "C");
        hash.Add("4", "D");
        hash.Add("5","E");
        hash.Add("6", "F");
        hash.Add("7", "G");
        hash.Add("8","H");
        hash.Add("9", "I");
        hash.Add("10", "J");
        Console.WriteLine("Is the Hashtable having fixed size? = " + hash.IsFixedSize);
    }
}

The output of the above code is −

Is the Hashtable having fixed size? = False

Using IsFixedSize with Hashtable Display

Example

using System;
using System.Collections;

public class Demo {
    public static void Main(){
        Hashtable hash = new Hashtable();
        hash.Add("One", "Katie");
        hash.Add("Two", "John");
        hash.Add("Three", "Barry");
        hash.Add("Four", "");
        hash.Add("Five","Harry");
        hash.Add("Six", "F");
        hash.Add("Seven", "Tom");
        hash.Add("Eight","Andy");
        hash.Add("Nine", "I");
        hash.Add("Ten", "Tim");
        Console.WriteLine("Hashtable Key and Value pairs...");
        foreach(DictionaryEntry entry in hash){
            Console.WriteLine("{0} and {1} ", entry.Key, entry.Value);
        }
        Console.WriteLine("Is the Hashtable having fixed size? = " + hash.IsFixedSize);
    }
}

The output of the above code is −

Hashtable Key and Value pairs...
One and Katie
Ten and Tim
Five and Harry
Three and Barry
Seven and Tom
Two and John
Four and
Eight and Andy
Nine and I
Six and F
Is the Hashtable having fixed size? = False

Creating a Fixed-Size Hashtable

To create a fixed-size Hashtable, you can use the Hashtable.Synchronized() method with a wrapper or use CollectionBase derived classes. Here's an example demonstrating the difference −

Example

using System;
using System.Collections;

public class Demo {
    public static void Main(){
        // Regular Hashtable
        Hashtable regularHash = new Hashtable();
        regularHash.Add("A", "Apple");
        regularHash.Add("B", "Banana");
        Console.WriteLine("Regular Hashtable IsFixedSize: " + regularHash.IsFixedSize);
        
        // Create a read-only wrapper (which is fixed-size)
        Hashtable readOnlyHash = Hashtable.ReadOnly(regularHash);
        Console.WriteLine("ReadOnly Hashtable IsFixedSize: " + readOnlyHash.IsFixedSize);
        Console.WriteLine("ReadOnly Hashtable IsReadOnly: " + readOnlyHash.IsReadOnly);
    }
}

The output of the above code is −

Regular Hashtable IsFixedSize: False
ReadOnly Hashtable IsFixedSize: True
ReadOnly Hashtable IsReadOnly: True

Conclusion

The IsFixedSize property helps determine whether a Hashtable allows adding or removing elements. Regular Hashtables return False, while wrapper collections like read-only Hashtables return True. This property is useful for validating collection behavior before performing operations.