What is the IsReadOnly property of Hashtable class in C#?

The IsReadOnly property of the Hashtable class in C# returns a boolean value indicating whether the Hashtable is read-only. When a Hashtable is read-only, you cannot add, remove, or modify its elements.

By default, all Hashtable instances created using the standard constructor are not read-only, meaning they allow modifications. However, you can create read-only wrappers using specific methods.

Syntax

Following is the syntax for accessing the IsReadOnly property −

bool isReadOnly = hashtable.IsReadOnly;

Return Value

The IsReadOnly property returns −

• true if the Hashtable is read-only
• false if the Hashtable allows modifications

Example with Regular Hashtable

The following example demonstrates checking the IsReadOnly property of a standard Hashtable −

using System;
using System.Collections;

class Program {
    static void Main(string[] args) {
        Hashtable ht = new Hashtable();
        ht.Add("One", "Amit");
        ht.Add("Two", "Aman");
        ht.Add("Three", "Raman");
        
        Console.WriteLine("IsReadOnly = " + ht.IsReadOnly);
        Console.WriteLine("Can modify: " + !ht.IsReadOnly);
        
        // Demonstrate modification is allowed
        ht["Four"] = "Suman";
        Console.WriteLine("Added new element successfully");
        Console.WriteLine("Total elements: " + ht.Count);
    }
}

The output of the above code is −

IsReadOnly = False
Can modify: True
Added new element successfully
Total elements: 4

Example with Read-Only Hashtable

You can create a read-only wrapper of a Hashtable using the Hashtable.Synchronized method or by creating a custom read-only implementation −

using System;
using System.Collections;

class Program {
    static void Main(string[] args) {
        // Create a regular hashtable
        Hashtable originalHt = new Hashtable();
        originalHt.Add("A", "Apple");
        originalHt.Add("B", "Banana");
        
        Console.WriteLine("Original Hashtable IsReadOnly: " + originalHt.IsReadOnly);
        
        // Create a synchronized version (still not read-only)
        Hashtable syncHt = Hashtable.Synchronized(originalHt);
        Console.WriteLine("Synchronized Hashtable IsReadOnly: " + syncHt.IsReadOnly);
        
        // Both allow modifications
        originalHt["C"] = "Cherry";
        syncHt["D"] = "Date";
        
        Console.WriteLine("Original Count: " + originalHt.Count);
        Console.WriteLine("Synchronized Count: " + syncHt.Count);
    }
}

The output of the above code is −

Original Hashtable IsReadOnly: False
Synchronized Hashtable IsReadOnly: False
Original Count: 4
Synchronized Count: 4

Common Use Cases

The IsReadOnly property is useful when −

• You need to verify if a Hashtable can be modified before attempting operations

• You're working with Hashtables from different sources and need to check their mutability

• You want to implement defensive programming practices by checking permissions before modifications

Example with Conditional Modification

using System;
using System.Collections;

class Program {
    static void SafeAdd(Hashtable ht, object key, object value) {
        if (ht.IsReadOnly) {
            Console.WriteLine("Cannot add - Hashtable is read-only");
        } else {
            ht.Add(key, value);
            Console.WriteLine($"Added {key}: {value}");
        }
    }
    
    static void Main(string[] args) {
        Hashtable ht = new Hashtable();
        ht.Add("Initial", "Value");
        
        Console.WriteLine("Hashtable IsReadOnly: " + ht.IsReadOnly);
        SafeAdd(ht, "New", "Element");
        
        Console.WriteLine("Final count: " + ht.Count);
    }
}

The output of the above code is −

Hashtable IsReadOnly: False
Added New: Element
Final count: 2

Conclusion

The IsReadOnly property of the Hashtable class provides a way to check whether the collection allows modifications. While standard Hashtables return false for this property, it's essential for ensuring safe operations when working with collections from various sources.