System.Collections Namespace

The System.Collections namespace contains interfaces and classes that define various collections of objects, such as lists, queues, bit arrays, hash tables, and dictionaries.

Core Types

ArrayList

Represents an ordered collection of objects that can be indexed individually.

Hashtable

Implements a collection of key/value pairs that are organized based on the hash code of the key.

Queue

Represents a first-in, first-out (FIFO) collection of objects.

Stack

Represents a last-in, first-out (LIFO) collection of objects.

SortedList

Represents a collection of key/value pairs that are sorted by the keys and are accessible by key and index.

BitArray

Manages a compact array of bit values, which are represented as Booleans, where true indicates that the bit is on (1) and false indicates the bit is off (0).

Example

using System;
using System.Collections;

class Program
{
    static void Main()
    {
        // Create an ArrayList and add items
        ArrayList list = new ArrayList();
        list.Add("Apple");
        list.Add("Banana");
        list.Add("Cherry");

        // Iterate over the collection
        foreach (var item in list)
        {
            Console.WriteLine(item);
        }

        // Use a Hashtable
        Hashtable table = new Hashtable();
        table[1] = "One";
        table[2] = "Two";

        Console.WriteLine($"Key 1 = {table[1]}");
    }
}