To analyze the differences and applications of [] List Array ArrayList in C

[] is for a specific type, fixed length.

List is type-specific and of arbitrary length.

Array is for any type, fixed length.

ArrayList is for any type, any length.

Array and ArrayList implement any type by storing object, so they are converted when used.

The sample application

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Web; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Collections; 
public partial class _Default : System.Web.UI.Page 
{ 
    protected void Page_Load(object sender, EventArgs e) 
    { 
        // System.Int32  Is the structure  
        int[] arr = new int[] { 1, 2, 3 }; 
        Response.Write(arr[0]); // 1 
        Change(arr); 
        Response.Write(arr[0]); // 2 
        // List  The namespace of is  System.Collections.Generic 
        List<int> list = new List<int>(); 
        list.Add(1); 
        list.Add(2); 
        list.Add(3); 
        Response.Write(list[0]); // 1 
        Change(list); 
        Response.Write(list[0]); // 2 
        // Array  The namespace of is  System 
        Array array = Array.CreateInstance(System.Type.GetType("System.Int32"), 3); // Array  Is an abstract class and cannot be used  new Array  To create.  
        array.SetValue(1, 0); 
        array.SetValue(2, 1); 
        array.SetValue(3, 2); 
        Response.Write(array.GetValue(0)); // 1 
        Change(array); 
        Response.Write(array.GetValue(0)); // 2 
        // ArrayList  The namespace of is  System.Collections 
        ArrayList arrayList = new ArrayList(3); 
        arrayList.Add(1); 
        arrayList.Add(2); 
        arrayList.Add(3); 
        Response.Write(arrayList[0]); // 1 
        Change(arrayList); 
        Response.Write(arrayList[0]); // 2 
    } 
    private void Change(int[] arr) 
    { 
        for (int i = 0; i < arr.Length; i++) 
        { 
            arr[i] *= 2; 
        } 
    } 
    private void Change(List<int> list) 
    { 
        for (int i = 0; i < list.Count; i++) //  use  Count 
        { 
            list[i] *= 2; 
        } 
    } 

    private void Change(Array array) 
    { 
        for (int i = 0; i < array.Length; i++) //  use  Length 
        { 
            array.SetValue((int)array.GetValue(i) * 2, i); //  Type conversion is required  
        } 
    } 
    private void Change(ArrayList arrayList) 
    { 
        for (int i = 0; i < arrayList.Count; i++) //  use  Count 
        { 
            arrayList[i] = (int)arrayList[i] * 2; //  Type conversion is required  
        } 
    } 
}

In addition.

Converting 1 object array to ArrayList USES the ArrayList.Adapter method. This method wraps 1 IList in 1 ArrayLIst.

Person[] personArray = myPerson.GetPersons();
ArrayList personList = ArrayList.Adapter(personArray);

Converting an ArrayList to an array of objects can use the ArrayList.ToArray method.

Person[] personArrayFromList = (Person[])personList.ToArray(typeof(Person));

Don't forget to cast before calling the ArrayList.ToArray method, otherwise an error will occur at compile time indicating that you cannot convert 1 ArrayList to an array of Person objects.