Use of ArrayList

using System;
using System.Collections;//arraylist The header file
using System.Collections.Generic;//list The header file
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication63
{
class fathder
{
}
class Program
{
ArrayList arrayList = new ArrayList();
List li = new List();// Definition list You have to define when list The type of ,arraylist no need
static void Main(string[] args)
{
arrayList.Add(10);// Any type can be specified when passing parameters inside
arrayList.Add(“nihao”);
arrayList.Add(new fathder());
foreach (var item in arrayList)// It can be used foreach facilitate ArrayList All elements are treated as object, So you need to force type conversion when accessing elements
{
Console.WriteLine(item);
}

        li.Add(5);// After specifying the type, only parameters of the specified type can be passed  List<T> Ensure the security of the type . There is no need for type conversion when getting elements 
      
        Console.ReadKey();
    }
}

}

ArrayList Class is a special array . It comes from System.Collections Namespace ; By adding and deleting elements , You can change the length of the array dynamically .

ArrayList initialization  ArrayList There are three kinds of initialization
 1） Do not initialize capacity   ArrayList al = new ArrayList();// Default capacity is 0, When the array capacity is full, the array will automatically change to the current array capacity 2 Double expansion
 
   2) Initialize capacity ArrayList al = new ArrayList(3);// The initial capacity is 3
 3） Initialize with a set or array ArrayList al = new ArrayList(a);//a For a collection or array
Additive elements
ArrayList arrayList = new ArrayList();
arrayList.Add(10);// Any type can be specified when passing parameters inside
arrayList.Add(“nihao”);
arrayList.Add(new fathder());
foreach (var item in arrayList)// It can be used foreach facilitate ArrayList All elements are treated as object, So you need to force type conversion when accessing elements
{
Console.WriteLine(item);
}
Remove elements
arrayList.Remove(object obj);// Remove... From the array obj Elements
 
arrayList.RemoveAt(int index);// Remove index to index Digital elements of
 
arrayList.RemoveRange(int indext,int count);// Remove from index index Start , remove count Elements
Look for the element
Find elements with Contains（）、IndexOf（）、LastIndexOf（）3 Medium method
al.Contains(object obj);// Find whether there is... In the array obj Elements , There is returned true;
 
IndexOf（） There are two overload methods   Usage is as follows ：
 
1）、al.IndexOf(object obj);// from 0 Start looking for obj Elements , Only the first obj Elements , And return the position in the array , If it doesn't exist , return -1;
 
2）、al.IndexOf(object obj,int startIndex); // from startIndex Start looking for obj Elements , Only the first obj Elements , And return the position in the array ,
 
3）、al.IndexOf(object obj,int startIndex,int count);  from startIndex Start thinking and find count Elements , If there is obj Elements , Returns its position in the array
 
  al.LastIndexOf() Methods and IndexOf（） The usage is the same , It also has two overloads , The difference is ,LastIndexOf（obj） Yes find to obj The last place
ArrayList The traversal
Count Property can be retrieved ArrayList Length of array , It can be used for Traversal array
 
                               for (int i = 0; i < al.Count;i++ )
 
                              {
 
                                           Console.Write("{0}\t",al[i]);
 
                              }
 
use foreach Traverse
 
foreach(object o in al)
 
                          {
 
                                  Console.Write("{0}\t", o);
 
                            }