Introduction
It is just like as array ,but always
dynamic and can hold any values unlike array. It is a data structure that holds
data in many different ways. The collection class is defined in the
System.Collections namespace. There are five types of collections in data
structure.
1.Hastable
2.Arraylist
3.Linkedlist
4.Stack
5.Queue
But mostly use of two types collections in C#,they are Hastable and Arraylist.
Here we will discuss about only Hastable and Arraylist.
1. Hastable
Hastable have two values i.e. key(id) and
item(value).
Why we use Hastable
If we want to stored data in two dimensional
array at run time then we use Hastable. For example, a months name and his
serial number and we can access there data using a key.
using
System;
using
System.Collections.Generic;
using
System.ComponentModel;
using
System.Data;
using
System.Drawing;
using
System.Linq;
using
System.Text;
using
System.Windows.Forms;
using
System.Collections;
namespace
hastable
{
public partial
class Form1
: Form
{
public Form1()
{
InitializeComponent();
}
private void
Form1_Load(object sender,
EventArgs e)
{
}
private void
button1_Click(object sender,
EventArgs e)
{
Hashtable hs =
new Hashtable();
hs.Add("1",
"January");
hs.Add("2",
"Febuary");
hs.Add("3",
"March");
hs.Add("4",
"April");
hs.Add("5","May");
hs.Add("6",
"june");
hs.Add("7",
"July");
hs.Add("8",
"August");
hs.Add("9",
"September");
hs.Add("10",
"October");
hs.Add("11",
"November");
hs.Add("12",
"December");
//MessageBox.Show(hs["8"].ToString());//
print one value(August)
foreach
(string k in
hs.Keys)
{
MessageBox.Show(hs[k].ToString());//print
all values
}
}
}
}
Now run the application.
Output (One value using key) looks like the below image.
Output (all values using foreach loop) looks like
the below image.
code description
In the above code first of all
we make the object of hastable i.e. hs. After that we add the key and value
using the hs object in the hastable. If we print the only one value then we will
give your key(id), which is shown above. If we print the all values then we use
foreach loop.
2. ArrayList
Arraylist have only one
values i.e. item(value) not a key(id).
Why we use
ArrayList
We know that array have a
fixed size. If we want to add items beyond the specified dimension then we use
Arraylist. If we want to insert an item in a list then we use Linked list but in
the C# we use Arraylist for that purpose.
using System;
using
System.Collections.Generic;
using
System.ComponentModel;
using
System.Data;
using
System.Drawing;
using
System.Linq;
using
System.Text;
using
System.Windows.Forms;
using
System.Collections;
namespace
arraylist
{
public partial
class Form1
: Form
{
public Form1()
{
InitializeComponent();
}
private void
button1_Click(object sender,
EventArgs e)
{
ArrayList al =
new ArrayList();
al.Add("January");
al.Add("Febuary");
al.Add("March");
al.Add("April");
al.Add("May");
al.Add("june");
al.Add("July");
al.Add("August");
al.Add("September");
al.Add("October");
al.Add("November");
al.Add("December");
//MessageBox.Show(al[0].ToString());//Print the one value
foreach (string
k in al)
{
MessageBox.Show(k.ToString());//
Print the all values
}
}
}
}
Now run the application.
Output (One value using index number) looks like the below image.
Output (all values using foreach loop) looks
like the below image.
0
code description
In
the above code first of all we make the object of Arraylist i.e. 'al'. After
that we add the value using the 'al' object in the Arraylist. If we print the
only one value then we will give index number, which is shown above. If we print
the all values then we use foreach loop.
Summary
Collections are very
important for stored data in the array and list. Collections solves the many
problem like as fixed array ,linked list etc. So collections are very useful for
solving these problems.