Can I have an ArrayList of ArrayLists in Java?
C# - ArrayListIn 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. Show An ArrayList can be used to add unknown data where you don't know the types and the size of the data. Create an ArrayListThe ArrayList class included in the System.Collections namespace. Create an object of the ArrayList using the new keyword. Example: Create an ArrayList using System.Collections;
ArrayList arlist = new ArrayList();
// or
var arlist = new ArrayList(); // recommended
Adding Elements in ArrayListUse 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 ArrayList var 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 ArrayListThe 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 ArrayList var 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 ArrayListThe 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 ArrayList ArrayList 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 ArrayListUse the Insert() method to insert an element at the specified index into an ArrayList. Signature: void Insert(int index, Object value) Example: Insert Element in ArrayList ArrayList 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 at the specfied index. Signature: Void InsertRange(int index, ICollection c) Example: Insert Collection in ArrayList ArrayList 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 ArrayListUse the Remove(), RemoveAt(), or RemoveRange methods to remove elements from an ArrayList. Example: Remove Elements from ArrayList ArrayList arList = new ArrayList()
{
1,
null,
"Bill",
300,
" ",
4.5f,
300,
};
arList.Remove(null); //Removes first occurance of null
arList.RemoveAt(4); //Removes element at index 4
arList.RemoveRange(0, 2);//Removes two elements starting from 1st item (0 index)
Try it Check Element in ArrayListUse 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 Elements ArrayList 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 it Note: It is not recommended to use the ArrayList class due to performance issue. Instead, use List ArrayList ClassThe following diagram illustrates the ArrayList class. ArrayList Properties
ArrayList Methods
Further Reading
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