Collections in C#

C# supports several collections including List, ArrayList, HashTable, SortedList, Stack, and Queue. Learn how to implement Collections In C#.

C# and .NET supports various collections. Collections in C# can be broken down into two categories, generic and non-generic. The following table lists and matches these classes. 

 Non-generic                          Generic
  ArrayList     ------------->          List
  HashTable  ------------->          Dictionary
  SortedList   ------------->          SortedList  
  Stack           ------------->          Stack
  Queue         ------------->          Queue

1. Non-Generic

  1. Each element can represent a value of a different type.
  2. Array Size is not fixed.
  3. Elements can be added / removed at runtime.

ArrayList

  1. Arraylist is a class that is similar to an array, but it can be used to store values of various types.
  2. An Arraylist doesn't have a specific size.
  3. Any number of elements can be stored.
  1. using System.Collections;

  2. protected void Button1_Click(object sender, EventArgs e)  
  3. {  
  4.      ArrayList al = new ArrayList();  
  5.      string str = "kiran teja jallepalli";  
  6.      int x = 7;  
  7.      DateTime d = DateTime.Parse("8-oct-1985");  
  8.      al.Add(str);  
  9.      al.Add(x);  
  10.      al.Add(d);  
  11.       
  12.      foreach (object o in al)  
  13.      {  
  14.         Response.Write(o);  
  15.         Response.Write("<br>");  
  16.      }   
  17. }
Output

kiran teja jallepalli
7
10/8/1985 12:00:00 AM
 
ForeachLoop

It executes for each and every item that exists in the arraylist object.

Every time the loop rotates it reads one item from the arraylist and assignes it to the variable.
 
Note:
Arraylist allocates memory for 4 items, whenever an object is created. When a fifth item is added, memory for another 4 items are added.
it reduces the memory allocated for the object.
 
Capacity: is a property that returns the number of items for which memory is allocated .
 

HashTable


HashTable is similar to arraylist but represents the items as a combination of a key and value.
  1. using System.Collections;

  2. protected void Button2_Click(object sender, EventArgs e)  
  3. {  
  4.     Hashtable ht = new Hashtable();  
  5.     ht.Add("ora""oracle");  
  6.     ht.Add("vb""vb.net");  
  7.     ht.Add("cs""cs.net");  
  8.     ht.Add("asp""asp.net");  
  9.   
  10.     foreach (DictionaryEntry d in ht)  
  11.     {  
  12.        Response.Write (d.Key + " " + d.Value);  
  13.   
  14.        Response.Write("<br>");  
  15.   
  16.     }  
  17. }
Output

vb  vb.net
asp asp.net
cs  cs.net
ora oracle 
 
DictonaryEntry: is a class whose object represents the data in a combination of key & value pairs.
 

SortedList

    1. Is a class that has the combination of arraylist and hashtable.
    2. Represents the data as a key and value pair.
    3. Arranges all the items in sorted order. 
    1. using System.Collections;

    2. protected void Button3_Click(object sender, EventArgs e)  
    3. {  
    4.      SortedList sl = new SortedList();  
    5.      sl.Add("ora""oracle");  
    6.      sl.Add("vb""vb.net");  
    7.      sl.Add("cs""cs.net");  
    8.      sl.Add("asp""asp.net");  
    9.              
    10.      foreach (DictionaryEntry d in sl)  
    11.      {  
    12.          Response.Write(d.Key + " " + d.Value);  
    13.          Response.Write("<br>");  
    14.   
    15.      }  
    16. }
    Output

    asp  asp.net
    cs   cs.net
    ora  oracle
    vb   vb.net
     

    Stack

    1. protected void Button4_Click(object sender, EventArgs e)  
    2. {  
    3.     Stack stk = new Stack();  
    4.     stk.Push("cs.net");  
    5.     stk.Push("vb.net");  
    6.     stk.Push("asp.net");  
    7.     stk.Push("sqlserver");  
    8.        
    9.     foreach (object o in stk)  
    10.     {  
    11.        Response.Write(o + "<br>");  
    12.     }  
    13. }
    Output

    sqlserver
    asp.net
    vb.net
    cs.net
     

    Queue

    1. using System.Collections;

    2. protected void Button5_Click(object sender, EventArgs e)  
    3. {  
    4.     Queue q = new Queue();  
    5.     q.Enqueue("cs.net");  
    6.     q.Enqueue("vb.net");  
    7.     q.Enqueue("asp.net");  
    8.     q.Enqueue("sqlserver");  
    9.          
    10.     foreach (object o in q)  
    11.     {  
    12.        Response.Write(o + "<br>");  
    13.     }  
    14. }

    Output

    cs.net
    vb.net
    asp.net
    sqlserver
     

    2. Generic Collections

     
    Generic Collections work on the specific type that is specified in the program whereas non-generic collections work on the object type. 
    1. Specific type
    2. Array Size is not fixed
    3. Elements can be added / removed at runtime.

    List

    1. using System.Collections.Generic;  
    2.   
    3. protected void Button1_Click(object sender, EventArgs e)  
    4. {  
    5.         List<int> lst = new List<int>();  
    6.         lst.Add(100);  
    7.         lst.Add(200);  
    8.         lst.Add(300);  
    9.         lst.Add(400);  
    10.         foreach (int i in lst)  
    11.         {  
    12.             Response.Write(i+"<br>");  
    13.         }  
    14.  }  

    Dictonary

    1. using System.Collections.Generic;    
    2.     
    3.  protected void Button1_Click(object sender, EventArgs e)    
    4.  {    
    5.      Dictionary<intstring> dct = new Dictionary<intstring>();    
    6.      dct.Add(1, "cs.net");    
    7.      dct.Add(2, "vb.net");    
    8.      dct.Add(3, "vb.net");    
    9.      dct.Add(4, "vb.net");    
    10.      foreach (KeyValuePair<intstring> kvp in dct)    
    11.      {    
    12.          Response.Write(kvp.Key + " " + kvp.Value);    
    13.          Response.Write("<br>");    
    14.      }          
    15.   }  

    SortedList

    1. using System.Collections.Generic;

    2. protected void Button3_Click(object sender, EventArgs e)  
    3. {  
    4. SortedList<stringstring> sl = new SortedList<stringstring>();  
    5. sl.Add("ora""oracle");  
    6. sl.Add("vb""vb.net");  
    7. sl.Add("cs""cs.net");  
    8. sl.Add("asp""asp.net");  
    9.   
    10. foreach (KeyValuePair<stringstring> kvp in sl)  
    11. {  
    12. Response.Write(kvp.Key + " " + kvp.Value);  
    13. Response.Write("<br>");  
    14. }  

    Stack

    1. using System.Collections.Generic; 

    2. protected void Button4_Click(object sender, EventArgs e)  
    3. {  
    4. Stack<string> stk = new Stack<string>();  
    5. stk.Push("cs.net");  
    6. stk.Push("vb.net");  
    7. stk.Push("asp.net");  
    8. stk.Push("sqlserver");  
    9.   
    10. foreach (string s in stk)  
    11. {  
    12. Response.Write(s + "<br>");  
    13. }  

    Queue

    1. using System.Collections.Generic;
    2. protected void Button1_Click(object sender, EventArgs e)  
    3.    {  
    4.    Queue<string> q = new Queue<string>();  
    5.   
    6.    q.Enqueue("cs.net");  
    7.    q.Enqueue("vb.net");  
    8.    q.Enqueue("asp.net");  
    9.    q.Enqueue("sqlserver");  
    10.   
    11.    foreach (string s in q)  
    12.    {  
    13.    Response.Write(s + "<br>");  
    14.    }  
    15.    }