Collection Class in C#

Last Updated : 10 Sep, 2025

The Collection<T> class is a generic collection in C# provided by the .NET framework under the System.Collections.ObjectModel namespace. It represents a dynamic, strongly typed list of objects that can be accessed by index (like a List<T>), but it is designed to be more extensible.

Syntax:

C# 
Collection<string> fruits = new Collection<string>();

Characteristics

  • Belongs to the System.Collections.ObjectModel namespace.
  • Stores elements of a specific type (T).
  • Provides methods to add, remove and search elements.
  • Allows index-based access like arrays and List<T>.
  • Designed for scenarios where you want to customize collection behavior by overriding methods.

Constructors

ConstructorDescription
Collection<T>()Initializes a new instance of the Collection<T> class that is empty.
Collection<T>(IList<T>)Initializes a new instance of the Collection<T> class as a wrapper for the specified list.

Example:

CSHARP 
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

class GFG {

    public static void Main(){
        
        Collection<int> myColl = new Collection<int>();

        // Adding elements in Collection myColl
        myColl.Add(2);
        myColl.Add(3);
        myColl.Add(4);
        myColl.Add(5);

        // Displaying the elements in myColl
        foreach(int i in myColl){
            Console.WriteLine(i);
        }
    }
}

Output
2
3
4
5

Collection Properties

PropertyDescription
CountGets the number of elements actually contained in the Collection<T>.
ItemsGets a IList<T> wrapper around the Collection<T>.
Item[Int32]Gets or sets the element at the specified index.

Example:

CSHARP 
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
 
class GFG {
 
    public static void Main()
    {
        // Creating a collection of strings
        Collection<string> myColl = new Collection<string>();
 
        // Adding elements in Collection myColl
        myColl.Add("A");
        myColl.Add("B");
        myColl.Add("C");
        myColl.Add("D");
        myColl.Add("E");

        // To print the count of elements in Collection
        Console.WriteLine("Count : " + myColl.Count);
 
        // Get the element at index 2
        Console.WriteLine("Element at index 2 is : " + myColl[2]);
 
        // Get the element at index 3
        Console.WriteLine("Element at index 3 is : " + myColl[3]);
    }
}

Output
Count : 5
Element at index 2 is : C
Element at index 3 is : D

Collection Methods

MethodDescription
Add(T)Adds an object to the end of the Collection<T>.
Clear()Removes all elements from the Collection<T>.
ClearItems()Removes all elements from the Collection<T>.
Contains(T)Determines whether an element is in the Collection<T>.
CopyTo(T[], Int32)Copies the elements of the collection to an array, starting at a specified index.
Equals(Object)Determines whether the specified object is equal to the current object.
GetEnumerator()Returns an enumerator that iterates through the Collection<T>.
GetHashCode()Serves as the default hash function.
GetType()Gets the Type of the current instance.
IndexOf(T)Searches for the object and returns the zero-based index of the first occurrence.
Insert(Int32, T)Inserts an element into the Collection<T> at the specified index.
InsertItem(Int32, T)Inserts an element into the Collection at the specified index.
MemberwiseClone()Creates a shallow copy of the current Object.
Remove(T)Removes the first occurrence of a specific object from the Collection<T>.
RemoveAt(Int32)Removes the element at the specified index of the Collection<T>.
RemoveItem(Int32)Removes the element at the specified index of the Collection<T>.
SetItem(Int32, T)Replaces the element at the specified index.
ToString()Returns a string that represents the current object.

Example 1:

CSHARP 
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

class GFG{

    public static void Main(){
        // Creating a collection of strings
        Collection<string> myColl = new Collection<string>();

        myColl.Add("A");
        myColl.Add("B");
        myColl.Add("C");
        myColl.Add("D");
        myColl.Add("E");

        // Check if an element exists in the Collection (returns true/false)
        Console.WriteLine(myColl.Contains("A"));
    }
}

Output
True

Example 2:

CSHARP 
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

class GFG{

    public static void Main(){
        // Creating a collection of strings
        Collection<string> myColl = new Collection<string>();

        myColl.Add("A");
        myColl.Add("B");
        myColl.Add("C");
        myColl.Add("D");
        myColl.Add("E");

        // Creating a string array
        string[] myArr = new string[myColl.Count];
     
        myColl.CopyTo(myArr, 0);

        foreach(string str in myArr){
            Console.WriteLine(str);
        }
    }
}

Output
A
B
C
D
E
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