Definition Of List<T>:
- List<T> class has been introduce in
framework 2
(also part of C# 2)
- This is part of generic feature of .Net and included in the namespace
System.Collections.Generic
. This is family of collection class and provide all the basic features of collection like add, remove, insert,foreach,find etc.
- This allow us to create strong type of list of objects which can be access by the index, also when create
List<T>
type of objects then it does not require boxing and un-boxing from the object class.
Syntax:
List<T> objectName=new List<T>();
Example code of List<T>
I. Create int-List<T> and retrieve data from object: Suppose we need to store bunch of numbers in a variable then we can take a List<int> variable:
//Creating List<T> int type object
List<int> number = new List<int>();
//Add item to List
number.Add(1);
number.Add(2);
number.Add(3);
number.Add(4);
//loop through all the item by foreach loop
foreach (int num in number)
{
Console.WriteLine(num);
}
//loop through all the item by for loop
//and get item by List index
for (int i = 0; i < number.Count;i++ )
{
Console.WriteLine(number[i]);
}
II. Create string-List<T> and retrieve data from object: Create a List with string type: Suppose we need to store bunch of geometrical shape in a variable then we can take a List<int>
variable:
//Creating List string type object
List geoShape = new List();
//Add item to List
geoShape.Add("Triangle");
geoShape.Add("Circle");
geoShape.Add("Square");
geoShape.Add("Rectangle");
//loop through all the item by foreach loop
foreach (string shape in geoShape)
{
Console.WriteLine(shape);
}
//loop through all the item by for loop
//and get item by List index
for (int i = 0; i < geoShape.Count; i++)
{
Console.WriteLine(geoShape[i]);
}
III. Create custom class-List<T> and retrieve data from object: Create a List with custom type: I have taken an example of product model class to explain how to add list of products value to the List<Product>
object.
public class Product
{
public int ID { get; set; }
public string Name { get; set; }
public float Price { get; set; }
}
class Program
{
static void Main(string[] args)
{
Product product = new Product();
//Creating List Product class type object
List productList = new List();
//There are other way to assign product data, i have use in way to easy to
//understand the beginner
product.ID = 1;
product.Name = "Demo Product 1";
product.Price = 400000;
//Add product data to product List
productList.Add(product);
product = new Product();
product.ID = 1;
product.Name = "Demo Product 1";
product.Price = 500000;
//Add product data to product List
productList.Add(product);
//loop through all the item by foreach loop
foreach (Product p in productList)
{
Console.WriteLine(p);
}
//loop through all the item by for loop
//and get item by List index
for (int i = 0; i < productList.Count; i++)
{
Console.WriteLine(productList[i]);
}
Console.ReadLine();
}
}
Interview Question on List<T>
- When we have array then why we require List<T>
- What is the difference between
array
and List<T>
- What is the difference between
ArrayList
and List<T>
- What is the difference between
IEnumerable
and List
<string>
- How to add item in the
List
or List<T>?
- How to count number of item in List<T>?
- What are the different way to retrieve complete data from the
List<T>
and which is the preferable?
- How to insert the data in
List<T>
at an index place?
- How to remove data from
List<T>?
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