C# Hashtable Explanation

In C#, a Hashtable is a collection class that implements a hash table data structure. It is part of the System.Collections namespace and provides a way to store and retrieve key-value pairs efficiently. The keys and values can be of any data type.

Here's an explanation of the Hashtable class and its main features:

1. Key-Value Pairs: A Hashtable stores data in key-value pairs. Each key must be unique within the Hashtable, and the value associated with each key can be accessed using that key.

2. Hashing: Internally, a Hashtable uses a hash function to compute an index into an array of buckets or slots, from which the desired value can be found.

3. Hashing Algorithm: The hash function is responsible for generating a hash code (an integer) from the key. The hash code is used to determine the bucket in which the key-value pair will be stored.

4. Collision Handling: Since multiple keys might hash to the same index (hash collision), the Hashtable implements collision handling techniques such as chaining or open addressing to handle these collisions and store multiple entries in the same bucket.

5. Dynamic Resizing: The Hashtable automatically resizes its internal array of buckets as needed to maintain an efficient load factor, which is the ratio of the number of entries to the number of buckets. This ensures that the Hashtable remains efficient even as the number of entries changes.

6. Performance and Efficiency: The Hashtable provides efficient access to elements using keys. The average time complexity for accessing an element is O(1), assuming a good hash function and minimal collisions.

7. Usage: To use a Hashtable, you create an instance of the class and then use the Add method to add key-value pairs, the Remove method to remove key-value pairs, and the ContainsKey method to check if a specific key exists. You can also use the indexer ([]) to access values based on keys.

Here's a simple example of using a Hashtable in C#:

using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        // Create a new Hashtable
        Hashtable hashtable = new Hashtable();

        // Add key-value pairs
        hashtable.Add("Name", "John");
        hashtable.Add("Age", 30);
        hashtable.Add("Country", "USA");

        // Access values using keys
        Console.WriteLine("Name: " + hashtable["Name"]);
        Console.WriteLine("Age: " + hashtable["Age"]);
        Console.WriteLine("Country: " + hashtable["Country"]);

        // Check if a key exists
        Console.WriteLine("Contains 'Name' key: " + hashtable.ContainsKey("Name"));

        // Remove a key-value pair
        hashtable.Remove("Age");

        // Check if a key exists after removal
        Console.WriteLine("Contains 'Age' key after removal: " + hashtable.ContainsKey("Age"));
    }
}

In this example, we create a Hashtable, add key-value pairs, access values using keys, check for key existence, and remove a key-value pair.