The List
Example: Creating a list of integers
List<int> numbers = new List<int> { 5, 2, 9 };
Key Features of List in C#
- Unlike arrays, List
can grow or shrink dynamically as elements are added or removed. - Allows duplicate elements and accepts null values for reference types.
- Provides built-in methods to add, remove, search, sort and manipulate elements.
- Not sorted by default, elements are accessed using a zero-based index.
- Capacity grows automatically when needed by reallocating the internal array.
- Generic equivalent of ArrayList, implementing IList
for type safety.
Declaration of List
List
listName = new List ();
Example: Creating a list, adding elements to it and then displaying the elements using the for-each loop.
using System;
using System.Collections.Generic;
class Geeks
{
static void Main()
{
// Create a new list of integers
List<int> l = new List<int>();
// Add elements to the list
l.Add(10);
l.Add(20);
l.Add(30);
l.Add(40);
// Display the elements in the list
Console.WriteLine("Elements in the list:");
foreach (int i in l){
Console.WriteLine(i);
}
}
}
Output
Elements in the list: 10 20 30 40
Constructors
| Constructors | Description |
|---|---|
| List | Initializes an empty list with the default initial capacity. |
| List | Initializes a list with elements copied from the specified collection, with capacity set to fit them. |
| List | Initializes an empty list with the specified initial capacity. |
Example: This example demonstrates how to create an empty List and display its initial count.
using System;
using System.Collections.Generic;
class Geeks {
public static void Main(String[] args){
// Creating a List of integers
List<int> l = new List<int>();
// displaying the number of elements of List
Output
0
Properties of List Class
The List class provides several properties to access its state.
| Properties | Description |
|---|---|
| Capacity | Gets or sets the total number of elements the internal data structure can hold without resizing. |
| Count | Gets the number of elements contained in the List |
| Item[Int32] | Gets or sets the element at the specified index. |
Example: This example, demonstrates the list capacity and count.
using System;
using System.Collections.Generic;
class Geeks {
public static void Main(String[] args){
// Creating a List of integers
List<int> l = new List<int>();
// Adding elements to the List one by one
l.Add(1);
l.Add(2);
l.Add(3);
l.Add(4);
l.Add(5);
l.Add(6);
// Printing the Capacity and Count of l
Console.WriteLine("Capacity: " + l.Capacity);
Console.WriteLine("Count: " + l.Count);
}
}
Output
Capacity: 8 Count: 6
Methods
| Method | Description |
|---|---|
| Add(T) | Adds an object to the end of the List |
| AddRange(IEnumerable | Adds elements of a collection to the end of the list. |
| AsReadOnly() | Returns a read-only wrapper for the list. |
| BinarySearch() | Searches for an element using binary search (list must be sorted). |
| Clear() | Removes all elements from the list. |
| Contains(T) | Determines whether an element is in the List |
| CopyTo() | Copies elements (or a range) to an array. |
| Exists(Predicate | Returns true if any element matches the condition. |
| Find(Predicate | Returns the first element matching a condition. |
| FindAll(Predicate | Returns all elements matching a condition. |
| FindIndex() | Returns the index of the first matching element. |
| FindLast(Predicate | Returns the last element matching a condition. |
| FindLastIndex() | Returns the index of the last matching element. |
| ForEach(Action | Performs the specified action on each element of the List |
| GetRange(int, int) | Creates a shallow copy of a range of elements in the source List |
| GetType() | Gets the Type of the current instance. |
| IndexOf() | Returns the index of the first occurrence of a value. |
| Insert(Int32, T) | Inserts an element into the List |
| InsertRange(Int32,IEnumerable<>) | Inserts a collection at a specific index. |
| LastIndexOf() | Returns the index of the last occurrence of a value. |
| Remove(T) | Removes the first occurrence of a specific object from the List |
| RemoveAll(Predicate | Removes all the elements that match the conditions defined by the specified predicate. |
| RemoveAt(Int32) | Removes the element at the specified index of the List |
| RemoveRange(Int32, Int32) | Removes a range of elements from the List |
| Reverse() | Reverses the order of the elements in the List |
| Sort() | Sorts the elements or a portion of the elements in the List |
| ToArray() | Copies the elements of the List |
| ToString() | Returns a string that represents the current object. |
| TrimExcess() | Sets the capacity to the actual number of elements in the List |
| TrueForAll(Predicate | Determines whether every element in the List |
Example 1: This example demonstrates how to check if a specified element is present in the list using Contains().
using System;
using System.Collections.Generic;
class Geeks {
public static void Main(String[] args)
{
// Creating an List of Integers
List<int> l = new List<int>();
// Adding elements to List
l.Add(1);
l.Add(2);
l.Add(3);
// Checking whether 2 is present in List or not
Console.Write("Element 2 is presnt in the List?: " + l.Contains(2));
}
}
Output
Element 2 is presnt in the List?: True
Example 2: This example printing the list before and after removing elements at specified index.
using System;
using System.Collections.Generic;
class Geeks {
public static void Main(String[] args)
{
// Creating a new List and adding elements to it
List<int> l = new List<int>();
l.Add(17);
l.Add(19);
l.Add(21);
l.Add(9);
l.Add(75);
l.Add(19);
l.Add(73);
// Printing the initial list
Console.WriteLine("Initial List: " + string.Join(", ", l));
// Removing elements from the list
l.RemoveAt(3);
l.Remove(19);
// Printing the updated list
Console.WriteLine("Updated List: " + string.Join(", ", l));
}
}
Output
Initial List: 17, 19, 21, 9, 75, 19, 73 Updated List: 17, 21, 75, 19, 73