Introduction
A List is one of the generic collection classes in the "System.Collection.Generic" namespace. There are several generic collection classes in the System.Collection.Generic namespace that includes the following:
- Dictionary
- List
- Stack
- Queue
A List class can be used to create a collection of any type. For example, we can create a list of Integers, strings and even any complex types.
Why use a List
- Unlike arrays, a List can grow in size automatically. In other words, a list can be re-sized dynamically but arrays cannot.
- List is a generic type.
- The List class also provides methods to search, sort and manipulate lists.
Example 1 - Using Array
I am taking an example to store data in an array and see what the problem is in storing the data in the array.
using System;
using System.Collections.Generic;
namespace List_Methods_Properties
{
class Program
{
static void Main(string[] args)
{
customer customer1 = new customer()
{
EmpID = 1,
EmpName = "Sourabh",
EmpSalary = 50000
};
customer customer2 = new customer()
{
EmpID = 2,
EmpName = "Shaili",
EmpSalary = 60000
};
customer customer3 = new customer()
{
EmpID = 3,
EmpName = "Saloni",
EmpSalary = 55000
};
//Customer array
customer[] customers = new customer[2];
customers[0] = customer1;
customers[1] = customer2;
//here I am adding one more cutomer to customers array and building the programs
customers[2] = customer3;
}
}
class customer
{
public int EmpID { get; set; }
public string EmpName { get; set; }
public int EmpSalary { get; set; }
}
}
In the example above, I have created one class named "customer" and In the main method I have created an array named customers with a size of two. When I build this program (using CTRL+SHIFT+B) then I will get output like built successfully but when I run this program then I get the error:
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When I run this program then at run time I will get the exception index was out of the bound of the array.
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So now we use List
A list is a generic data type that can hold any type of data that may be integer, float, string or may be complex type. To create a list we have 3 types of constructors.
List<Type> Customers = new List<Type>();//default constructor
List<Type> Customers = new List<Type>(int capacity);//with spacific capacity
List<Type> Customers = new List(IEnumerable<Type> collection);//with spacific collection
Example 2 - Using List
using System;
using System.Collections.Generic;
namespace List_Methods_Properties
{
class Program
{
static void Main(string[] args)
{
customer customer1 = new customer()
{
EmpID = 1,
EmpName = "Sourabh",
EmpSalary = 50000
};
customer customer2 = new customer()
{
EmpID = 2,
EmpName = "Shaili",
EmpSalary = 60000
};
customer customer3 = new customer()
{
EmpID = 3,
EmpName = "Saloni",
EmpSalary = 55000
};
//using list
// Creating List with initial capacity 2
List<customer> Customers = new List<customer>(2);
Customers.Add(customer1); // Here Add Method is used to add the item to the list
Customers.Add(customer2);
//adding one more customer wheather capacity is 2 only
Customers.Add(customer3);
}
}
class customer
{
public int EmpID { get; set; }
public string EmpName { get; set; }
public int EmpSalary { get; set; }
}
}
Output
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In the preceding example we are adding 3 items to the list wereas the capacity is only two so it proves that a List can be automatically re-sized.
Add Method
Add method is used to add the items to the list.
How to access items from the C# List
To add the item to the list we use an index number to access it.
// <List Item>[index number]
Code
using System;
using System.Collections.Generic;
namespace List_Methods_Properties
{
class Program
{
static void Main(string[] args)
{
customer customer1 = new customer()
{
EmpID = 1,
EmpName = "Sourabh",
EmpSalary = 50000
};
customer customer2 = new customer()
{
EmpID = 2,
EmpName = "Shaili",
EmpSalary = 60000
};
customer customer3 = new customer()
{
EmpID = 3,
EmpName = "Saloni",
EmpSalary = 55000
};
//using list
// Creating List with initial capacity 2
List<customer> Customers = new List<customer>(2);
Customers.Add(customer1);
Customers.Add(customer2);
Customers.Add(customer3);
//Accessing Item from the List
customer c1 = Customers[0];
Console.WriteLine("ID={0}, Name={1}, Salary={2}",c1.EmpID,c1.EmpName,c1.EmpSalary);
customer c2 = Customers[1];
Console.WriteLine("ID={0}, Name={1}, Salary={2}", c2.EmpID, c2.EmpName, c2.EmpSalary);
customer c3 = Customers[2];
Console.WriteLine("ID={0}, Name={1}, Salary={2}", c3.EmpID, c3.EmpName, c3.EmpSalary);
}
}
class customer
{
public int EmpID { get; set; }
public string EmpName { get; set; }
public int EmpSalary { get; set; }
}
}
How to access all the items of the list using foreach loop,
using System;
using System.Collections.Generic;
namespace List_Methods_Properties
{
class Program
{
static void Main(string[] args)
{
customer customer1 = new customer()
{
EmpID = 1,
EmpName = "Sourabh",
EmpSalary = 50000
};
customer customer2 = new customer()
{
EmpID = 2,
EmpName = "Shaili",
EmpSalary = 60000
};
customer customer3 = new customer()
{
EmpID = 3,
EmpName = "Saloni",
EmpSalary = 55000
};
//using list
// Creating List with initial capacity 2
List<customer> Customers = new List<customer>(2);
Customers.Add(customer1);
Customers.Add(customer2);
Customers.Add(customer3);
//Accessing Item from the List using for loop
foreach (customer c in Customers)
{
Console.WriteLine("ID={0}, Name={1}, Salary={2}", c.EmpID, c.EmpName, c.EmpSalary);
}
}
}
class customer
{
public int EmpID { get; set; }
public string EmpName { get; set; }
public int EmpSalary { get; set; }
}
}
Output
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Note
You can also use for or while loop to access all the items.
Different Properties of a C# List
- Count: This property is the number of items of the List.
- Capacity: This property is the capacity of the List. By default the capacity is 0, then starts with 4, 8, 16, 32.....
using System;
using System.Collections.Generic;
namespace List_Methods_Properties
{
class Program
{
static void Main(string[] args)
{
List<string> Names = new List<string>();
Names.Add("Sourabh");
Names.Add("Shaili");
Names.Add("Saloni");
Console.WriteLine("Number of Items in the List is:" + Names.Count);
Console.WriteLine("Capacity of the List is:" + Names.Capacity);
}
}
}
Output
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Different Methods of a C# List
- Contains: This method determines whether or not an element is in the List, if the element is present in the List then this method returns "True" else "False".
- Insert: This method is used to insert an element at a specific index.
- Remove: This method removes the first occurrence of the specific object from the list.
- RemoveAll: This method removes all the elements that matches the condition.
- RemoveAt: This method remove the element from the specified index.
- Clear: Removes all the element from the list.
- Sort: This method is used sort the List
- Reverse: This method reverses the order of the elements in the entire List.
- TrimExcess: This method sets the capacity to the actual number of elements in the list.
Example
using System;
using System.Collections.Generic;
namespace List_Methods_Properties
{
class Program
{
static void Main(string[] args)
{
List<string> Names = new List<string>();
Names.Add("Sourabh");
Names.Add("Shaili");
Names.Add("Saloni");
Names.Add("Ankit");
Names.Add("Bill");
Names.Add("Dinesh");
Names.Add("Mahesh Chand");
Names.Add("DJ");
Names.Add("Rajesh");
Names.Add("Rajesh");
Names.Add("Rajesh");
//Contains: This method determines that weather the element is in List or not,
//If element is present in List then this method returns "True" else return "False".
Console.WriteLine(Names.Contains("Sourabh\n"));
//accessing all the element from the list
foreach (string Name in Names)
{
Console.WriteLine(Name);
}
//Insert: This method is used to insert an element in particular index.
Names.Insert(5, "Rajesh");
Console.WriteLine("\n\nAfter Inserting Rajesh at 5th index");
foreach (string Name in Names)
{
Console.WriteLine(Name);
}
//Sort: Sorts the List
Names.Sort();
Console.WriteLine("\n\nSorting in List");
foreach (string Name in Names)
{
Console.WriteLine(Name);
}
//Reverse: Reverse the order of the element of List
Names.Reverse();
Console.WriteLine("\n\nReverse Elements of List");
foreach (string Name in Names)
{
Console.WriteLine(Name);
}
//Remove: Removes the elements from the list
Names.Remove("Rajesh");
Console.WriteLine("\n\nRemove Element from the List using Remove Method");
foreach (string Name in Names)
{
Console.WriteLine(Name);
}
//RemoveAt:Remove the elements from the list at the specific index
Names.RemoveAt(7);
Console.WriteLine("\n\nRemove Element from the List using RemoveAt Method");
foreach (string Name in Names)
{
Console.WriteLine(Name);
}
//nTrimExcess:Sets the capacity to the actual number of elements in the List
Names.TrimExcess();
Console.WriteLine("\n\nTrimExcess Method");
Console.WriteLine("Capacity: {0}", Names.Capacity);
Console.WriteLine("Count: {0}", Names.Count);
//Clear:Removes all elements from the List
Names.Clear();
Console.WriteLine("\n\nClear Method");
Console.WriteLine("Capacity: {0}", Names.Capacity);
Console.WriteLine("Count: {0}", Names.Count);
Console.ReadKey();
}
}
}
Output
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In this article, we saw some use cases of List<T>.
Further readings
Basic Introduction to List In C# and .NET Core