Collection and Arrays in .Net

Difference Between String and StringBuilder

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String Class	StringBuilder
Once the string object is created, its length and content cannot be modified.	Even after object is created, it can be able to modify length and content.
Slower	Faster

Example of Single Dimension Array in .Net

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int [] intArray = new int[3];

intArray[2] = 22; // set the third element to 22

Example of Multi Dimension Array in .Net

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int [][] myTable = new int[2,3];

myTable[1,2] = 22;

Example of Jagged Array in .Net : Variable Length Array in .Net

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int [][] myTable = new int[3][];

myTable[0] = new int[5];

myTable[1] = new int[2];

myTable[2] = new int[4];

myTable[0][2] = 11;

Example of String Array in .Net

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string []names = new string[4];

names[2] = “God will make me win”;

Limitation of Arrays

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The size of an array is always fixed and must be defined at the time of instantiation of an array.
Secondly, an array can only contain objects of the same data type, which we need to define at the time of its instantiation.

Collections in .Net : Namespace for Collections in .Net

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System.Collections namespace

ArrayList Concept in .Net

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Provides a collection similar to an array, but that grows dynamically as
the number of elements change.

Example

static void Main()
{
    ArrayList list = new ArrayList();
    list.Add(11);
    list.Add(22);
    list.Add(33);
    foreach(int num in list)
    {
        Console.WriteLine(num);
    }
}

Output
11
22
33

Stack Concept in .Net

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A collection that works on the Last In First Out (LIFO) principle,
i.e., the last item inserted is the first item removed from the collection. 
Push - To add element and 
Pop – To Remove element

Example

using System;
using System.Collections;

class Test
{
    static void Main()
    {
        Stack stack = new Stack();
        stack.Push(2);
        stack.Push(4);
        stack.Push(6);
       
        while(stack.Count != 0)
        {
            Console.WriteLine(stack.Pop());
        }
    }
}

Output
6
4
2

Queue Concept in .Net

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A collection that works on the First In First Out (FIFO) principle, i.e.,
the first item inserted is the first item removed from the collection.  
Enqueue - To add element and Dequeue – To Remove element

Example:

static void Main()
{
    Queue queue = new Queue();
    queue.Enqueue(2);
    queue.Enqueue(4);
    queue.Enqueue(6);
   
    while(queue.Count != 0)
    {
        Console.WriteLine(queue.Dequeue());
    }
}

Output
2
4
6

Dictionaries Concept in .Net

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Dictionaries are a kind of collection that store items in a key-value pair fashion.

System.Collections namespace

Hashtable Concept in .Net

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Provides a collection of key-value pairs that are organized
based on the hash code of the key.

Example:
static void Main()
{
    Hashtable ht =  new Hashtable(20);
    ht.Add("ht01", "DotNetGuts");
    ht.Add("ht02", "EasyTutor.2ya.com");
    ht.Add("ht03", "DailyFreeCode.com");
   
    Console.WriteLine("Printing Keys...");
    foreach(string key in ht.Keys)
    {
        Console.WriteLine(key);
    }
   
    Console.WriteLine("\nPrinting Values...");
    foreach(string Value in ht.Values)
    {
        Console.WriteLine(Value);
    }
   
    Console.WriteLine("Size of Hashtable is {0}", ht.Count);
   
    Console.WriteLine(ht.ContainsKey("ht01"));
    Console.WriteLine(ht.ContainsValue("DailyFreeCode.com"));
   
    Console.WriteLine("\nRemoving element with key = ht02");
    ht.Remove("ht02");
   
    Console.WriteLine("Size of Hashtable is {0}", ht.Count);
   
}

Output

Printing Keys...
ht01
ht02
ht03

Printing Values...
DotNetGuts
EasyTutor.2ya.com
DailyFreeCode.com
Size of Hashtable is 3
True
True
 
Removing element with key = ht02
Size of Hashtable is 2

SortedList Concept in .Net

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Provides a collection of key-value pairs where the items are sorted according to the key. The items are accessible by both the keys and the index.

Example:

 static void Main()
{
  SortedList sl =  new SortedList();
  sl.Add(18, "Java");
  sl.Add(5, "C#");
  sl.Add(11, "VB.Net");
  sl.Add(1, "C++.Net");

  Console.WriteLine("The items in the sorted order are...");
  Console.WriteLine("\t Key \t\t Value");
  Console.WriteLine("\t === \t\t =====");
  for(int i=0; i<sl.Count; i++)
  {
      Console.WriteLine("\t {0} \t\t {1}",  sl.GetKey(i),
      sl.GetByIndex(i));
  }
}

Output

Key Value

==
1 C++.Net
5 C#
11 VB.Net
18 Java