List Collection Class in C#

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:

1. Dictionary
2. List
3. Stack
4. 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 to use a List

1. Unlike arrays, a List can grow in size automatically in other words a list can be re-sized dynamically but arrays cannot.
   
   
2. List is a generic type.
   
   
3. 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: 

 

 

 

When I run this program then at run time I will get the exception index was out of the bound of the array.

 

 

 

 

 

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: 

 

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 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

   

Note: You can also use for or while loop to access all the items.

Different Properties of a "List":

1. Count: This property is the number of items of the List.
   
   
2. 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

  

 Different Methods of a "List":

1. 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".
   
   
2. Insert: This method is used to insert an element at a specific index.
   
   
3. Remove: This method removes the first occurrence of the specific object from the list.
   
   
4. RemoveAll: This method removes all the elements that matches the condition.
   
   
5. RemoveAt: This method remove the element from the specified index.
   
   
6. Clear: Removes all the element from the list.
   
   
7. Sort: This method is used sort the List
   
   
8. Reverse: This method reverses the order of the elements in the entire List.
   
   
9. 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