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Home Forums Difference between Hashtable and Dictionary – MindStick
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Ashutosh Patel
Ashutosh Patel 13 Jun 2024
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Dictionary vs Hashtable in C#

In C#, Hashtable and Dictionary are used to store key-value pairs, but they have some differences in terms of functionality, implementation and features,

Dictionary 

There are several points in Dictionary that make it different from Hashtable which are as follows,

Namespace- Dictionary is present in the System.Collections.Generic namespace.

Type Safety- The Dictionary is type-safe, you must specify the data type for both the keys and the values ​​when you declare it.

Performance- Dictionary usually provides better performance than Hashtable since it is a generic collection and avoids boxing/unboxing overhead

Null Keys- the Dictionary does not allow the null key but allows null values.

Enumeration- Enumerating over a dictionary with foreach is more efficient than enumerating over a hashtable.

Enumeration Order- Dictionary does not guarantee the order of the elements while Hashtable also does not preserve the order of the elements.

Obsolete- The dictionary is a newer and preferred alternative to key-value pairs in most cases.

Example- 

using System;
using System.Collections.Generic;
class Program
{
   static void Main()
   {
       // Creating a Dictionary
       Dictionary<string, string> dictionary = new Dictionary<string, string>();
       // Adding key-value pairs to the Dictionary
       dictionary.Add("1", "One");
       dictionary.Add("2", "Two");
       dictionary.Add("3", "Three");
       // Accessing elements in the Dictionary
       Console.WriteLine("Value at key '1': " + dictionary["1"]);
       Console.WriteLine("Value at key '2': " + dictionary["2"]);
       Console.WriteLine("Value at key '3': " + dictionary["3"]);
       // Iterate over dictionary
       Console.WriteLine("\n Iterate over dictionary:");
       foreach (KeyValuePair<string, string> pair in dictionary)
       {
           Console.WriteLine("Key: " + pair.Key + ", Value: " + pair.Value);
       }
       Console.ReadLine();
   }
}

Output-

Value at key '1': One
Value at key '2': Two
Value at key '3': Three

Iterate over dictionary:
Key: 1, Value: One
Key: 2, Value: Two
Key: 3, Value: Three

Hashtable

There are also some points in Hashtable that differ from Dictionary which are as follow,

Namespace- Dictionary is present in the System.Collections namespace.

Type Safety- The Hashtable is not type-safe, because it allows any datatype for both key and value.

Performance- Hashtable uses a simple hash code algorithm that's why its performance is not as good as Dictionary

Null Keys- The Hashtable allows both the null key and null value

Enumeration- Hashtable needs boxing/unboxing, which can degrade performance during calculation.

Enumeration Order- The Hashtable doesn't preserve the order of the elements.

Obsolete- The Hashtable is a part of an older non-generic collection framework in C#

Example- 

using System;
using System.Collections;
class Program
{
   static void Main()
   {
       // Creating a Hashtable
       Hashtable hashtable = new Hashtable();
       // Adding key-value pairs to the Hashtable
       hashtable.Add("1", "One");
       hashtable.Add("2", "Two");
       hashtable.Add("3", "Three");
       // Accessing elements in the Hashtable
       Console.WriteLine("Value at key '1': " + hashtable["1"]);
       Console.WriteLine("Value at key '2': " + hashtable["2"]);
       Console.WriteLine("Value at key '3': " + hashtable["3"]);
       // Iterating through the Hashtable
       Console.WriteLine("\nIterating through the Hashtable:");
       foreach (DictionaryEntry entry in hashtable)
       {
           Console.WriteLine("Key: " + entry.Key + ", Value: " + entry.Value);
       }
   }
}

Output-

Value at key '1': One
Value at key '2': Two
Value at key '3': Three

Iterating over the Hashtable:
Key: 2, Value: Two
Key: 3, Value: Three
Key: 1, Value: One

Also, Read: Pascal Triangle

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