Understanding Collections and Collections Interfaces

Collections in C#: An Overview

A collection is a set of related objects. Unlike arrays, a collection can grow and shrink dynamically as the number of objects added or deleted. A collection is a class, so you must declare a new collection before you can add elements to that collection. In this C# Tutorial, we will explore collections-and-collections-interfaces which will include What are collections in c#, What are collections interfaces in c#, and What types of collections interfaces are in c#.

What is Collections?

The .NET Framework provides various collections like ArrayList, HashTable, SortedList, Stack, and Queue, etc. All these collections exist in the System. Collections namespace.

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Example of Collections:

 using System; 
using System.Collections; 

class Scholarhat { 
	
	public static void Main() 
	{ 
		
		Queue CourseQueue = new  Queue(); 

		CourseQueue.Enqueue("C#"); 
		CourseQueue.Enqueue("Java"); 
		CourseQueue.Enqueue("SQL"); 
		CourseQueue.Enqueue("Python"); 
		CourseQueue.Enqueue("C"); 

		Console.Write("Total number of courses present in the Queue are: "); 

		Console.WriteLine(CourseQueue.Count); 

		// Displaying the beginning element of Queue 
		Console.WriteLine("Course: " + CourseQueue.Peek()); 
	} 
}     

Output

 Total number of courses present in the Queue are: 5
Course: C#

Explanation

What are Collection Interfaces?

All of the collection types use some common interfaces. These common interfaces define the basic functionality for each collection class. The key collections interfaces are – IEnumerable, ICollection, IDictionary, and IList.

IEnumerable acts as a base interface for all the collection types that is extended by ICollection. ICollection is further extended by IDictionary and IList.

All collections interfaces are not implemented by all the collections. It depends on the collection's nature.

The IEnumerable Interface: Syntax

 public IEnumerator GetEnumerator(  )
{
    return (IEnumerator) new ListBoxEnumerator(this);
}   

• Here The Enumerator must implement the IEnumerator methods and properties.
• These can be implemented either directly by the container class or by a separate class.
• The latter approach is preferred because it encapsulates this responsibility in the Enumerator class.

The ICollectionInterface: Syntax

 ICollection names = new List();
names.Add("Pragati");
names.Remove("surbhi");
Console.WriteLine(names.Count); // Outputs the count of items

The IDictionary: Syntax

 IDictionary ages = new();
ages["Pragati"] = 18;
ages.Add("surbhi", 17);
Console.WriteLine(ages["Pragati"]); // Access value by key

The IList: Syntax

 IList numbers = new List { 1, 2, 3,4,5 };
numbers[0] = 10; // Access and modify elements by index
Console.WriteLine(numbers.IndexOf(3)); // Outputs the index of '5'

Conclusion:

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