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C# – ArrayList
In C#, the ArrayList is a non-generic collection of objects whose size increases dynamically. It is the same as Array except that its size increases dynamically.
Nội dung chính
- C# – ArrayListCreate an ArrayListAdding Elements in ArrayListAccessing an ArrayListIterate an ArrayListInsert Elements in ArrayListRemove Elements from ArrayListCheck Element in ArrayListArrayList ClassArrayList PropertiesArrayList MethodsVideo liên quan
An ArrayList can be used to add unknown data where you don’t know the types and the size of the data.
Create an ArrayList
The ArrayList class included in the System.Collections namespace. Create an object of the ArrayList using the new keyword.
Example: Create an ArrayListusing System.Collections;
ArrayList arlist = new ArrayList();
// or
var arlist = new ArrayList(); // recommended
Adding Elements in ArrayList
Use the Add() method or object initializer syntax to add elements in an ArrayList.
An ArrayList can contain multiple null and duplicate values.
Example: Adding Elements in ArrayList// adding elements using ArrayList.Add() method
var arlist1 = new ArrayList();
arlist1.Add(1);
arlist1.Add(“Bill”);
arlist1.Add(” “);
arlist1.Add(true);
arlist1.Add(4.5);
arlist1.Add(null);
// adding elements using object initializer syntax
var arlist2 = new ArrayList()
2, “Steve”, ” “, true, 4.5, null
;
Try it
Use the AddRange(ICollection c) method to add an entire Array, HashTable, SortedList, ArrayList, BitArray, Queue, and Stack in the ArrayList.
Example: Adding Entire Array/ArrayList into ArrayListvar arlist1 = new ArrayList();
var arlist2 = new ArrayList()
1, “Bill”, ” “, true, 4.5, null
;
int[] arr = 100, 200, 300, 400 ;
Queue myQ = new Queue();
myQ.Enqueue(“Hello”);
myQ.Enqueue(“World!”);
arlist1.AddRange(arlist2); //adding arraylist in arraylist
arlist1.AddRange(arr); //adding array in arraylist
arlist1.AddRange(myQ); //adding Queue in arraylist
Try it
Accessing an ArrayList
The ArrayList class implements the IList interface. So, elements can be accessed using indexer, in the same way as an array. Index starts from zero and increases by one for each subsequent element.
An explicit casting to the appropriate types is required, or use the var variable.
Example: Accessing Elements of ArrayListvar arlist = new ArrayList()
1,
“Bill”,
300,
4.5f
;
//Access individual item using indexer
int firstElement = (int) arlist[0]; //returns 1
string secondElement = (string) arlist[1]; //returns “Bill”
//int secondElement = (int) arlist[1]; //Error: cannot cover string to int
//using var keyword without explicit casting
var firstElement = arlist[0]; //returns 1
var secondElement = arlist[1]; //returns “Bill”
//var fifthElement = arlist[5]; //Error: Index out of range
//update elements
arlist[0] = “Steve”;
arlist[1] = 100;
//arlist[5] = 500; //Error: Index out of range
Try it
Iterate an ArrayList
The ArrayList implements the ICollection interface that supports iteration of the collection types. So, use the foreach and the for loop to iterate an ArrayList. The Count property of an ArrayList returns the total number of elements in an ArrayList.
Example: Iterate ArrayListArrayList arlist = new ArrayList()
1,
“Bill”,
300,
4.5F
;
foreach (var item in arlist)
Console.Write(item + “, “); //output: 1, Bill, 300, 4.5,
for(int i = 0 ; i < arlist.Count; i++)
Console.Write(arlist[i] + “, “); //output: 1, Bill, 300, 4.5,
Try it
Insert Elements in ArrayList
Use the Insert() method to insert an element the specified index into an ArrayList.
Signature: void Insert(int index, Object value)
Example: Insert Element in ArrayListArrayList arlist = new ArrayList()
1,
“Bill”,
300,
4.5f
;
arlist.Insert(1, “Second Item”);
foreach (var val in arlist)
Console.WriteLine(val);
Try it
Use the InsertRange() method to insert a collection in an ArrayList the specfied index.
Signature: Void InsertRange(int index, ICollection c)
Example: Insert Collection in ArrayListArrayList arlist1 = new ArrayList()
100, 200, 600
;
ArrayList arlist2 = new ArrayList()
300, 400, 500
;
arlist1.InsertRange(2, arlist2);
foreach(var item in arlist1)
Console.Write(item + “, “); //output: 100, 200, 300, 400, 500, 600,
Try it
Remove Elements from ArrayList
Use the Remove(), RemoveAt(), or RemoveRange methods to remove elements from an ArrayList.
Example: Remove Elements from ArrayListArrayList arList = new ArrayList()
1,
null,
“Bill”,
300,
” “,
4.5f,
300,
;
arList.Remove(null); //Removes first occurance of null
arList.RemoveAt(4); //Removes element index 4
arList.RemoveRange(0, 2);//Removes two elements starting from 1st item (0 index)
Try it
Check Element in ArrayList
Use the Contains() method to determine whether the specified element exists in the ArrayList or not. It returns true if exists otherwise returns false.
Example: Check for ElementsArrayList arList = new ArrayList()
1,
“Bill”,
300,
4.5f,
300
;
Console.WriteLine(arList.Contains(300)); // true
Console.WriteLine(arList.Contains(“Bill”)); // true
Console.WriteLine(arList.Contains(10)); // false
Console.WriteLine(arList.Contains(“Steve”)); // false
Try itNote:It is not recommended to use the ArrayList class due to performance issue. Instead, use List<object> to store heterogeneous objects. To store data of same data type, use Generic List<T>.
ArrayList Class
The following diagram illustrates the ArrayList class.
C# ArrayList
ArrayList Properties
PropertiesDescriptionCapacityGets or sets the number of elements that the ArrayList can contain.CountGets the number of elements actually contained in the ArrayList.IsFixedSizeGets a value indicating whether the ArrayList has a fixed size.IsReadOnlyGets a value indicating whether the ArrayList is read-only.ItemGets or sets the element the specified index.
ArrayList Methods
MethodsDescriptionAdd()/AddRange()Add() method adds single elements the end of ArrayList.
AddRange() method adds all the elements from the specified collection into ArrayList.Insert()/InsertRange()Insert() method insert a single elements the specified index in ArrayList.
InsertRange() method insert all the elements of the specified collection starting from specified index in ArrayList.Remove()/RemoveRange()Remove() method removes the specified element from the ArrayList.
RemoveRange() method removes a range of elements from the ArrayList.RemoveAt()Removes the element the specified index from the ArrayList.Sort()Sorts entire elements of the ArrayList.Reverse()Reverses the order of the elements in the entire ArrayList.ContainsChecks whether specified element exists in the ArrayList or not. Returns true if exists otherwise false.ClearRemoves all the elements in ArrayList.CopyToCopies all the elements or range of elements to compitible Array.GetRangeReturns specified number of elements from specified index from ArrayList.IndexOfSearch specified element and returns zero based index if found. Returns -1 if element not found.ToArrayReturns compitible array from an ArrayList.Further Reading
- Difference between Array & ArrayListArrayList’s Methods & Properties
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