Difference between hashtable and dictionary in C#

In this article, we will discuss the difference between Hashtable and Dictionary in C#. But before discussing their differences, we must know about the Hashtable and Dictionary.

Key-value pairs can be stored in C# using either Dictionary or Hashtable data structures, but they have different features and implementations.

Hash Table:

• The System includes a collection class called Hashtable.Namespace for collections.
• Key-value pairs are kept as objects in this non-generic collection.
• Hashtable is based on the hash table data structure, in which elements are kept in buckets according to the key's hash code.
• It provides a quick method of using keys to access elements.
• Null can be a key and a value in a Hashtable.
• We can store any kind of key and value because it is not type-safe.
• Hashtable read operations are thread-safe, but write operations are not. When using a Hashtable in a multi-threaded environment, write operations must be manually synchronized.
• A Hashtable's enumeration may not always occur in the same sequence that the elements were added.

Dictionary:

• A general collection class in the System is called Dictionary.Collections.generic namespace.
• Dictionary was added to the .NET Framework 2.0 and requires explicit typing for both keys and values.
• Similar to Hashtable, it is based on a hash table data structure.
• As dictionaries offer type safety, we can designate the kinds of keys and values that they can store.
• It lets elements be retrieved more quickly with keys.
• Null values can be stored in dictionaries, but null keys cannot.
• There is no thread safety for any operation in Dictionary, unlike Hashtable. The ConcurrentDictionary class or manual access synchronization should be used if thread safety is needed.
• The sequence in which elements are added to a dictionary is not always guaranteed to be maintained when enumerated.

Main Difference between the Hashtable and Dictionary in C#.

There are several main differences between the Hashtable and Dictionary in C#. Some main differences between these methods are as follows:

Example:

Let us take an example to illustrate the Hashtable and Dictionary in C#.

using System;

using System.Collections; // Required for Hashtable

using System.Collections.Generic; // Required for Dictionary

class Program

{

    static void Main(string[] args)

    {

        // Hashtable example

        Hashtable hashtable = new Hashtable();

        hashtable.Add("key1", "value1");

        hashtable.Add("key2", "value2");

        hashtable.Add("key3", "value3");

        Console.WriteLine("Hashtable Example:");

        foreach (DictionaryEntry entry in hashtable)

        {

            Console.WriteLine($"Key: {entry.Key}, Value: {entry.Value}");

        }

        // Dictionary example

        Dictionary<string, string> dictionary = new Dictionary<string, string>();

        dictionary.Add("key1", "value1");

        dictionary.Add("key2", "value2");

        dictionary.Add("key3", "value3");

        Console.WriteLine("\nDictionary Example:");

        foreach (KeyValuePair<string, string> entry in dictionary)

        {

            Console.WriteLine($"Key: {entry.Key}, Value: {entry.Value}");

        }

        Console.ReadLine();

    }

}

Output:

Hashtable Example:Key: key1, Value: value1Key: key3,

Value: value3Key: key2, Value: value2

Dictionary Example:Key: key1, Value: value1Key: key2,

Value: value2Key: key3, Value: value3

Explanation:

In this example, this C# code shows how to initialize, add key-value pairs, and iterate over the elements of a hashtable and dictionary. We can see that Dictionary uses generics to provide type safety and more readable syntax.

Example 2:

Let us take another example to illustrate the Hashtable and Dictionary in C#.

using System;

using System.Collections; // Required for Hashtable

using System.Collections.Generic; // Required for Dictionary

class Program

{

    static void Main(string[] args)

    {

        // Hashtable example

        Hashtable hashtable = new Hashtable();

        hashtable.Add("key1", "value1");

        hashtable.Add("key2", "value2");

        hashtable.Add("key3", "value3");

        Console.WriteLine("Hashtable Example:");

        PrintValue(hashtable, "key2");

        // Remove a key from Hashtable

        RemoveKey(hashtable, "key1");

        // Try accessing a non-existent key

        PrintValue(hashtable, "key1");

        // Dictionary example

        Dictionary<string, string> dictionary = new Dictionary<string, string>();

        dictionary.Add("key1", "value1");

        dictionary.Add("key2", "value2");

        dictionary.Add("key3", "value3");

        Console.WriteLine("\nDictionary Example:");

        PrintValue(dictionary, "key2");

        // Remove a key from Dictionary

        RemoveKey(dictionary, "key1");

        // Try accessing a non-existent key

        PrintValue(dictionary, "key1");

        Console.ReadLine();

    }

    static void PrintValue(IDictionary collection, string key)

    {

        try

        {

            Console.WriteLine($"Value for key '{key}': {collection[key]}");

        }

        catch (Exception ex)

        {

            Console.WriteLine($"Error accessing key '{key}': {ex.Message}");

        }

    }

    static void RemoveKey(IDictionary collection, string key)

    {

        try

        {

            collection.Remove(key);

            Console.WriteLine($"Key '{key}' removed successfully.");

        }

        catch (Exception ex)

        {

            Console.WriteLine($"Error removing key '{key}': {ex.Message}");

        }

    }

}

Output:

Hashtable Example:

Value for key 'key2': value2

Key 'key1' removed successfully.

Value for key 'key1':

Dictionary Example:

Value for key 'key2': value2

Key 'key1' removed successfully.

Value for key 'key1':