What is Difference between Dictionary And Hashtable In C#?

In this article we understand Dictionary and Hashtable.
Dictionary and Hashtable are both used to hold the data as key-value pairs in C#.

Dictionary
The Dictionary type provides fast lookups with keys to get values. With it we use keys and values of any type, including ints and strings. Dictionary requires a special syntax form.

• Dictionary is generic type Dictionary<TKey,TValue>
• Dictionary class is a strong type < TKey,TValue > Hence, you must specify the data types for key and value.
• There is no need of boxing/unboxing.
• When you try to access non existing key dictionary, it gives runtime error.
• Dictionary maintains an order of the stored values.
• There is no need of boxing/unboxing, so it is faster than Hashtable.

public class Dict
{
    static void Main()
    {
       // Example Dictionary again
       Dictionary<string, int> d = new Dictionary<string, int>()
       {
           {"Cat", 2},  {"dog", 1}};
           // Loop over pairs with foreach
           foreach (KeyValuePair<string, int> pair in d)
           {
               Console.WriteLine ("{0}, {1}",pair.Key,  pair.Value);
           }
           foreach (var pair in d)
           {
               Console.WriteLine("{0}, {1}", pair.Key, pair.Value);
           }
           Console.ReadKey();
       }
    }
Hashtable

• Hashtable is non-generic type.
• Hashtable is a weakly typed data structure, so you can add keys and values of any object type.
• Values need to have boxing/unboxing.
• When you try to access non existing key Hashtable, it gives null values.
• Hashtable never maintains an order of the stored values.
• Hashtable needs boxing/unboxing, so it is slower than Dictionary.

using System.Collections;
class Program
{
    static Hashtable GetHashtable()
    {
        // Create and return new Hashtable.
        Hashtable hashtable = new Hashtable();
        hashtable.Add("Delhi", 1000);
        hashtable.Add("Varansi", 55);
        hashtable.Add("Mumbai", 540);
        return hashtable;
    }
    public  static void Main()
    {
        Hashtable hashtable = GetHashtable();
        // See if the Hashtable contains this key.
        Console.WriteLine(hashtable.ContainsKey("Varansi"));
        // Test the Contains method. It works the same way.
        Console.WriteLine(hashtable.Contains("Mumbai"));
        // Get value of Mumbai with indexer.
        int value = (int)hashtable["Mumbai"];
        // Write the value of Mumbai.
        Console.WriteLine(value);
    }
}

output
True
True
1000