COLLECTIONS IN C#

collection in c#

COLLECTIONS IN C#

"Collections in c# are a dynamic array means it can store multiples items/values as object type like array."  
Collection contain of many classes like ArrayList, Hashtable, Stack, Queue, Linkedlist, Sortedlist and many more in .net

Why we use Collections instead of Array

            The collection is came into play to eliminate some drawback of an array that's are

1- We cannot increase the size of array ones it formed means if we want to increase the size then we can do it by two methods. Either we make a new array and copy the values form old to new. Or we can do this with the help of Array. Resize keyword but the drawback is it destroy the existing array and create a new array by adding the old values into the new one.

2- The second draw back of an array is we cannot add a value in the middle of an array it's not possible with an array.

3- Thirds drawback is we can't delete a value form the middle of an array

            But with the help of collection we can performed the above three task smoothly because it contain a property call  auto resizing, that's mean whenever we keep adding the value this size of collection increasing automatically by adding one new box to the dynamic array¹. Second we can add a new value in the middle of a Collection²  and lastly Collection allow us to delete a value from its middle³.  Follow the link to see detail with example.

            However the Collection contains multiple classes under the namespace System. Collections such as ArrayList, Hashtable, Stack, Queue, Linkedlist, Sortedlist and many more in .net all these classes are defined in the library and we just use it. These collections are Non-Generic Collections

            When we came across using the Collection then the most using collection is the ArrayList

SYNTAX OF COLLECTION (ARRAYLIST)

     ArrayList <name> = new ArrayList ( );

    After then we can add Object values in the ArrayList

c# collection example 

Example of Arraylist (Collection)

class Program

{

  static void Main(string[] args)

 {

   ArrayList list = new ArrayList();

   Console.Write("Enter items/ values = ");

   list.Add(Console.ReadLine());

   list.Add(100); list.Add(200); list.Add(300);

   foreach (object obj in list)

   Console.WriteLine(obj);

   Console.ReadKey();

 }

}

Capacity of ArrayList

            In ArrayList there is property called as Capacity that show you how many items can store in the Collection (ArrayList), but it is not fixed

early at the initial stage the capacity will show you 0 zero capacity value because we do not insert any values yet, but after adding an item the Capacity automatically change, the capacity of storing item will 4 after adding 4 item it will auto increase by 8 and will keep the doubling of storing capacity as item reached the maximum so on, remember it is not fixed you can add item as you want. You can see the capacity of an ArrayList with the keyword <Name>. Capacity

Example to check Capacity of a Collections

            NOTE: Don't forget to add the directive System.Collections

static void Main(string[] args)

{

  ArrayList list = new ArrayList();       

  Console. WriteLine ("capacity ="+ list. Capacity);  //OUTPUT WILL ZERO

   }

Now try this

static void Main(string[] args)

{

  ArrayList list = new ArrayList();

  Console.WriteLine(list.Capacity);           //OUTPUT WILL ZERO 

  list.Add(4);

  Console.WriteLine(list.Capacity);           //OUTPUT WILL 4

  Console.ReadKey();

}

            In the above examples we use the default constructor which has 0 initial capacity but we can specify the initial capacity like this

static void Main(string[] args)

{

  ArrayList list = new ArrayList(10);

  Console.WriteLine(list.Capacity);       //OUTPUT WILL 10

  list.Add(4);

  Console.WriteLine(list.Capacity);       //OUTPUT WILL 10

  Console.ReadKey();

}