C# Collection & Generics Tutorials
Collections are data structures that holds data in different
ways for flexible operations . C# Collection classes are defined as part of the
System.Collections or System.Collections.Generic namespace.
How to use C# ArrayList Class
ArrayList is one of the most flexible data structure from
CSharp Collections. ArrayList contains a simple list of values. ArrayList
implements the IList interface using an array and very easily we can add ,
insert , delete , view etc. It is very flexible because we can add without any
size information , that is it will grow dynamically and also shrink .
c-sharp-arraylist
Add : Add an Item in
an ArrayList
Insert : Insert an
Item in a specified position in an ArrayList
Remove : Remove an
Item from ArrayList
RemoveAt: remove an
item from a specified position
Sort : Sort Items in
an ArrayList
How to add an Item in an ArrayList ?
Syntax :
ArrayList.add(object)
object : The Item to
be add the ArrayList
ArrayList arr;
arr.Add("Item1");
How to Insert an Item in an ArrayList ?
Syntax :
ArrayList.insert(index,object)
index : The position
of the item in an ArrayList
object : The Item to
be add the ArrayList
ArrayList arr;
arr.Insert(3,
"Item3");
How to remove an item from arrayList ?
Syntax :
ArrayList.Remove(object)
object : The Item to
be add the ArrayList
arr.Remove("item2")
How to remove an item in a specified position from an
ArrayList ?
Syntax :
ArrayList.RemoveAt(index)
index : the position
of an item to remove from an ArrayList
ItemList.RemoveAt(2)
How to sort ArrayList ?
Syntax :
ArrayList.Sort()
The following CSharp source code shows some function in
ArrayList
using System;
using System.Collections;
using System.Windows.Forms;
namespace WindowsApplication1
{
public partial class
Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void
button1_Click(object sender, EventArgs e)
{
int i = 0;
ArrayList
ItemList = new ArrayList();
ItemList.Add("Item4");
ItemList.Add("Item5");
ItemList.Add("Item2");
ItemList.Add("Item1");
ItemList.Add("Item3");
MessageBox.Show ("Shows Added
Items");
for (i = 0; i
< = ItemList.Count - 1; i++)
{
MessageBox.Show(ItemList[i].ToString());
}
//insert an
item
ItemList.Insert(3, "Item6");
//sort itemms in an arraylist
ItemList.Sort();
//remove an
item
ItemList.Remove("Item1");
//remove item
from a specified index
ItemList.RemoveAt(3);
MessageBox.Show("Shows final Items the ArrayList");
for (i = 0; i
< = ItemList.Count - 1; i++)
{
MessageBox.Show(ItemList[i].ToString());
}
}
}
}
When you execute this C# program , at first add five items
in the arraylist and displays. Then again one more item inserted in the third
position , and then sort all items. Next it remove the item1 and also remove
the item in the third position . Finally it shows the existing items.
Qns. What the
difference is between add and insert method in arraylist ?
Ans. Add will always add the element at the end of the ArrayList
while Insert allows you to choose what index you want your element to be. If
you always want the element placed at the end of the list then Add is what
you.
How to use C# HashTable Class
Hashtable in C# represents a collection of key/value pairs
which maps keys to value. Any non-null object can be used as a key but a value
can. We can retrieve items from hashTable to provide the key .
Both keys and
values are Objects.
The commonly used functions in Hashtable are :
Add : To add a pair of value
in HashTable
ContainsKey : Check if a specified key exist or not
ContainsValue : Check the specified Value exist in HashTable
Remove : Remove the specified Key and
corresponding Value
Add : To add a pair of value in HashTable
Syntax :
HashTable.Add(Key,Value)
Key : The Key value
Value : The value of
corresponding key
Hashtable ht;
ht.Add("1", "Sunday");
ContainsKey : Check if a specified key exist or not
Synatx : bool
HashTable.ContainsKey(key)
Key : The Key value for search
in HahTable
Returns : return
true if item exist else false
ht.Contains("1");
ContainsValue : Check the specified Value exist in HashTable
Synatx : bool
HashTable.ContainsValue(Value)
Value : Search the
specified Value in HashTable
Returns : return
true if item exist else false
ht.ContainsValue("Sunday")
Remove : Remove the specified Key and corresponding Value
Syntax :
HashTable.Remove(Key)
Key : The key of the
element to remove
ht.Remove("1");
The following source code shows some important operations in
a HashTable
using System;
using System.Collections;
using System.Windows.Forms;
namespace WindowsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Hashtable weeks = new Hashtable();
weeks.Add("1", "SunDay");
weeks.Add("2", "MonDay");
weeks.Add("3", "TueDay");
weeks.Add("4", "WedDay");
weeks.Add("5", "ThuDay");
weeks.Add("6", "FriDay");
weeks.Add("7", "SatDay");
//Display a single Item
MessageBox.Show(weeks["5"].ToString ());
//Search an Item
if (weeks.ContainsValue("TueDay"))
{
MessageBox.Show("Find");
}
else
{
MessageBox.Show("Not find");
}
//remove an Item
weeks.Remove("3");
//Display all key value pairs
foreach (DictionaryEntry day in weeks )
{
MessageBox.Show (day.Key + " - " + day.Value );
}
}
}
}
When you execute this C# program it will add seven entries
in the hashtable. The first message it will display the item 5. Then it check
the value "TueDay" is existing or not . Next it remove the third item
from HashTable. Finaly it displays all items exist in the HashTable.
How to use C# Stack Class
The Stack class represents a last-in-first-out
(LIFO) Stack of Objects. Stack follows the push-pop operations. That is we
can Push (insert) Items into Stack and Pop (retrieve) it back . Stack is
implemented as a circular buffer. It follows the Last In First Out (LIFO)
system. That is we can push the items into a stack and get it in reverse order.
Stack returns the last item first. As elements are added to a Stack, the
capacity is automatically increased as required through reallocation.
Commonly used methods :
Push : Add (Push) an item in the Stack data
structure
Pop : Pop return the last Item from the Stack
Contains:
Check the object contains in the Stack
Push : Add (Push) an item in the Stack data structure
Syntax :
Stack.Push(Object)
Object : The item to
be inserted.
Stack days = new
Stack();
days.Push("Sunday");
Pop : Pop
return the item last Item from the Stack
Syntax : Object
Stack.Pop()
Object : Return the
last object in the Stack
days.Pop();
Contains : Check the object contains in the Stack
Syntax :
Stack.Contains(Object)
Object : The
specified Object to be search
days.Contains("Tuesday");
The following CSharp Source code shows some of important
functions in Stack Class:
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
namespace WindowsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Stack days = new Stack();
days.Push("SunDay");
days.Push("MonDay");
days.Push("TueDay");
days.Push("WedDay");
days.Push("ThuDay");
days.Push("FriDay");
days.Push("SaturDay");
if (days.Count ==7)
{
MessageBox.Show(days.Pop().ToString ());
}
else
{
MessageBox.Show("SaturDay does not exist");
}
}
}
}
When you execute this C# program add seven items in the
stack . Then it check the count is equal to 7 , if it is seven then pop() the
item. The message box will display SaturDay.
How to use C# Queue Class
The Queue works like FIFO system , a
first-in, first-out collection of Objects. Objects stored in a Queue are
inserted at one end and removed from the other. The Queue provide additional
insertion, extraction, and inspection operations. We can Enqueue (add)
items in Queue and we can Dequeue (remove from Queue ) or we can Peek
(that is we will get the reference of first item ) item from Queue. Queue
accepts null reference as a valid value and allows duplicate elements.
Some important functions in the Queue Class are follows :
Enqueue : Add
an Item in Queue
Dequeue :
Remove the oldest item from Queue
Peek :
Get the reference of the oldest item
Enqueue : Add an Item in Queue
Syntax :
Queue.Enqueue(Object)
Object : The item to
add in Queue
days.Enqueue("Sunday");
Dequeue : Remove the oldest item from Queue (we don't
get the item later)
Syntax : Object
Queue.Dequeue()
Returns : Remove the
oldest item and return.
days.Dequeue();
Peek : Get the reference of the oldest item (it is
not removed permanently)
Syntax : Object
Queue.Peek()
returns : Get the
reference of the oldest item in the Queue
days.peek();
The following CSharp Source code shows some of commonly used
functions :
using System;
using System.Collections;
using System.Windows.Forms;
namespace WindowsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
Queue days = new Queue();
days.Enqueue("Sunday");
days.Enqueue("Monday");
days.Enqueue("Tuesday");
days.Enqueue("Wednsday");
days.Enqueue("Thursday");
days.Enqueue("Friday");
days.Enqueue("Saturday");
MessageBox.Show (days.Dequeue().ToString ());
if (days.Contains("Monday"))
{
MessageBox.Show("The queue contains Monday");
}
else
{
MessageBox.Show("Does not match any entries");
}
}
}
}
When you execute the above C# source code , you will get
Sunday in the message box and then it check the Monday is exist in the queue or
not.
How to use C# NameValueCollection Class
NameValueCollection is used to store a collection of
associated String keys and String values that can be accessed either with the
key or with the index. It is very similar to C# HashTable, HashTable also
stores data in Key , value format .
NameValueCollection can hold multiple string values under
a single key. As elements are added to a NameValueCollection, the capacity
is automatically increased as required through reallocation. The one important
thing is that you have to import System.Collections.Specialized Class in your
program for using NameValueCollection.
Adding new pairs
NameValueCollection.Add(name,value)
NameValueCollection
pair = new NameValueCollection();
pair.Add("High", "80");
Get the value of corresponding Key
string[]
NameValueCollection.GetValues(index);
NameValueCollection
pair = new NameValueCollection();
pair.Add("High", "80");
string[] vals =
pair.GetValues(1);
using System;
using System.Collections;
using System.Windows.Forms;
using System.Collections.Specialized;
namespace WindowsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
NameValueCollection markStatus = new NameValueCollection();
string[] values = null;
markStatus.Add("Very High", "80");
markStatus.Add("High", "60");
markStatus.Add("medium", "50");
markStatus.Add("Pass", "40");
foreach (string key in markStatus.Keys)
{
values = markStatus.GetValues(key);
foreach (string value in values)
{
MessageBox.Show (key + " - " + value);
}
}
}
}
}
C# Array Examples
Arrays are using for store similar data types
grouping as a single unit. We can access Array elements by its numeric index. The
array indexes start at zero. The default value of numeric array elements
are set to zero, and reference elements are set to null .
Integer Array
Declaring and Initializing an Integer Array
int[] array = new int[4];
array[0] = 10;
array[1] = 20;
array[2] = 30;
array[3] = 40;
In the above code we declare an Integer Array of four
elements and assign the value to array index . That means we assign values to
array index 0 - 4.
We can retrieve these values from array by using a for loop.
for
(int i = 0; i < array.Length; i++)
{
MessageBox.Show
(array[i]);
}
Initialize Array
Also we can declare and initialize an array in one
statement.
int[]
array = new int[] {10, 20, 30, 40};
Note that in the above code we did not specify the length of
the array so the compiler will do it for us.
How to find the length of an Array ?
Array.Length
We can use array.Length to find the length of an Array.
String Array
Declaring and Initializing a String Array
string[] week = new string[7];
week[0] = "Sunday";
week[1] = "Monday";
The above C# code declare a string array of 7 strings and
assign some values to it.
string[] week = new string[]
{"Sunday","Monday","Tuesday"};
The above code declare and initialize a string array with
values.
string str = week[1];
We can access the Arrays elements by providing its numerical
index, the above statement we access the second value from the week Array.
In the following program , we declare an Array
"week" capable of seven String values and assigns the seven values as
days in a week . Next step is to retrieve the elements of the Array using a for
loop . For finding the end of an Array we used the Length function of Array
Object.
string[] week =
new string[7];
week[0] =
"Sunday";
week[1] =
"Monday";
week[2] =
"Tuesday";
week[3] =
"Wednsday";
week[4] =
"Thursday";
week[5] =
"friday";
week[6] =
"Saturday";
for (int i = 0; i
< = week.Length-1; i++)
{
MessageBox.Show(week[i]);
}
How to resize an Array
An array can be resized with Array.Resize < T
> Method , that means We make an array bigger or smaller. Array.Resize
< T > Method Changes the number of elements of a one-dimensional array to
the specified new size.
Array.Resize < T > - T is the type of the elements of
the array.
This method should be used with only one dimensional Array.
This method allocates a new array with the specified size, copies elements from
the old array to the new one, and then replaces the old array with the new one.
Resize Array
// Initialize
array for example
char[] array = new
char[5];
array[0] = 'A';
array[1] = 'B';
array[2] = 'C';
array[3] = 'D';
array[4] = 'E';
for (int i = 0; i
< array.Length; i++)
{
MessageBox.Show (array[i].ToString ());
}
Array.Resize(ref
array, 3);
for (int i = 0; i
< array.Length; i++)
{
MessageBox.Show(array[i].ToString ());
}
Array.Resize(ref array, 3);
In the above code we resize the array to 3 elements.
for..each loop and array
int[]
array = { 10, 30, 50 }; //array declaration
foreach
(int element in array)
{
Console.WriteLine(element);
}
Array Sort
sort array in c# ascending descending Reverse array
You can sort the arrays in ascending order as well as
descending . We can use Array.Sort method for sorts the elements in a
one-dimensional array. Also we can use Array.Reverse method for reverses the
sequence of the elements in the entire one-dimensional Array. Click the
following link to see .... How to sort C# Arrays
Sort an Integer array in Ascending order
The following source code shows how to sort an integer Array
in ascending order.
C#
int[] array = new int[] { 3, 1, 4, 5, 2 };
Array.Sort(array);
foreach (var str in array)
{
MessageBox.Show(str.ToString());
}
Sort an Integer array in Descending order
The following code shows how to sort an Integer array in
reverse order.
C#
int[] array = new int[] { 3, 1, 4, 5, 2 };
Array.Sort(array);
Array.Reverse(array);
foreach (var str in array)
{
MessageBox.Show(str.ToString());
}
LINQ OrderByDescending
You can use LINQ OrderByDescending method to reverse
an array. OrderByDescending method sorts elements from high to low. The
following C# source code shows how to sort an array in descending order by
using LINQ OrderByDescending.
string[] array = new string[] { "a",
"b", "c", "d" };
array = array.OrderByDescending(c => c).ToArray();
foreach (var str in array)
{
MessageBox.Show(str.ToString());
}
How to Create an Array with different data types
You can create an array with elements of different data
types when declare the array as Object. Since System.Object is the base class
of all other types, an item in an array of Objects can have a reference to any
other type of object. More about.... Multiple data types in an Array
Multiple data types in an Array
No, we cannot store multiple datatype in an Array, we can
store similar datatype only in an Array.
How to Create an Array with different data types
How to store multiple datatypes in an array? interview
questions and answers c# vb.net asp.net
You can create an array with elements of different data
types when declare the array as Object. Since System.Object is the base
class of all other types, an item in an array of Objects can have a reference
to any other type of object.
Ex:
object[] mixedArray = new object[4];
mixedArray[0]=10;
mixedArray[1]="Jack";
mixedArray[2]=true;
mixedArray[3]=System.DateTime.Now;
In order to retrieve different data types from an Object
array, you can convert an element to the appropriate data type.
int id = int.Parse(mixedArray(0));
DateTime admissionDate = DateTime.Parse(mixedArray(3));
NOTE: If you want to store different data types in an
Array, better use System.Collections.ArrayList.
ArrayList Class
ArrayList Class in .Net framework
ArrayList is basically an alternative to an array. It is one
of the most flexible data structure from .Net Framework. It also allow dynamic
memory allocation(DML), adding, searching and sorting items in the list. More
about.... ArrayList
Array Example
Arrays are using for store similar data types grouping as a
single unit. We can access Array elements by its numeric index. The array
indexes start at zero. More about.... Array
System.Array.CopyTo and System.Array.Clone()
The System.Array.CopyTo method copies the elements
into another pre-existing array starting from a given index. The System.Array.Clone()
method returns a new array object, which means that the destination array
need not exist yet since a new one is created from scratch with containing all
the elements in the original array. More about the difference between ....
System.Array.CopyTo and System.Array.Clone()
Difference between System.Array.CopyTo and
System.Array.Clone()
.Net interview questions and answers C# vb.net asp.net
The System.Array.CopyTo method copies the elements
into another pre-existing array starting from a given index. In this case the
destination array need to already exist. Moreover, the target Object needs to
be sufficient to hold all the elements in the source array from the index you
specify as the destination. When perform CopyTo() method both arrays
must be single dimensional.
The System.Array.Clone() method returns a new array
object, which means that the destination array need not exist yet since a new
one is created from scratch with containing all the elements in the original
array. The Clone() method works on both single and multi-dimensional
arrays.
Performance wise System.Array.CopyTo is faster than Clone
when copying to array of same type.
Shallow copy and Deep copy
.Net Frequently asked questions and answers C# vb.net
asp.net
In .Net Shallow copy and deep copy are used for copying
data between objects. Shallow copying is creating a new object and
then copying the non-static fields of the current object to the new object. If
the field is a value type, a bit by bit copy of the field is performed. While Deep
copy is creating a new object and then copying the non-static fields of the
current object to the new object. If a field is a value type, a bit by bit copy
of the field is performed. More about... Difference between Shallow copy and
Deep copy
Array Example
Arrays are using for store similar data types grouping as a
single unit. We can access Array elements by its numeric index. The array
indexes start at zero. More about.... Array
How to check if a value exists in an array ?
The following program shows how to find an element from an
Array
Difference between Shallow copy and Deep copy
An object copy is a process where a data object has its
attributes copied to another object of the same data type. In .Net Shallow copy
and deep copy are used for copying data between objects.
What is Shallow copy ?
Shallow copying is creating a new object and then copying
the non-static fields of the current object to the new object. If the field is
a value type, a bit by bit copy of the field is performed. If the field is a
reference type, the reference is copied but the referred object is not,
therefore the original object and its clone refer to the same object. A shallow
copy of an object is a new object whose instance variables are identical to the
old object. In .Net shallow copy is done by the object method
MemberwiseClone().
The situations like , if you have an object with values and
you want to create a copy of that object in another variable from same type,
then you can use shallow copy, all property values which are of value types
will be copied, but if you have a property which is of reference type then this
instance will not be copied, instead you will have a reference to that instance
only.
What is Deep copy ?
Deep copy is creating a new object and then copying
the non-static fields of the current object to the new object. If a field is a
value type, a bit by bit copy of the field is performed. If a field is a
reference type, a new copy of the referred object is performed. A deep copy of
an object is a new object with entirely new instance variables, it does not
share objects with the old. While performing Deep Copy the classes to be cloned
must be flagged as [Serializable].
Deep copy is intended to copy all the elements of an object,
which include directly referenced elements of value type and the indirectly
referenced elements of a reference type that holds a reference to a memory
location that contains data rather than containing the data itself.
