ArrayList class

In this article, we will discuss ArrayList class – one of the List implemented class in detail



  • ArrayList is implementation class of List interface (i.e.; ArrayList implements List)
  • ArrayList uses resizable array or grow-able array to store element/objects
  • Duplicate element/objects are allowed to be inserted
  • Insertion order is maintained
  • Allows NULL insertion (no limit, we can insert any number of NULL to ArrayList)
  • Without generics, ArrayList allows to insert any type of objects; with generics, it is type-bounded (except, if we take Object as type within angle brackets)
  • Element retrieval is faster as ArrayList works on zero-based index
  • Manipulation (i.e.; addition/deletion of element from middle of ArrayList) is very slow, as it requires lot of shifting work internally
  • ArrayList is non-synchronized
  • Present in java.util package and extends java.util.AbstractList implements java.util.List interface
  • Also, implements java.util.RandomAccess, java.lang.Cloneable, marker interfaces which provides special ability to ArrayList (provided by JVM at run time)

Random Access: to access any random element/objects with same speed

Cloneable: to create a duplicate object or to clone an object

Serializable: to transfer objects across network


Source: Team BenchResources.Net


ArrayList constructors:

ArrayList al = new ArrayList();

  • creates an empty ArrayList object of size 10
  • when maximum size of the ArrayList is reached, then new ArrayList of bigger size is created using below formula
    Capacity: New ArrayList size = (current size * 3/2) + 1;
  • old ArrayList item values will be copied into new ArrayList


ArrayList al = new ArrayList(int initialCapacity);

  • creates an empty ArrayList object of specified size (or initial capacity)
  • when maximum size is reached, above formula will be applied and new ArryaList will be created


ArrayList al = new ArrayList(Collection c);

  • created an equivalent ArrayList object for the specified collection
  • it is basically used for inter-conversion between collection objects


ArrayList examples:


import java.util.ArrayList;

public class ArrayListAddAndRemove {

	public static void main(String[] args) {

		// creating ArrayList object of type String
		ArrayList<String> al = new ArrayList<String>();

		// adding elements to ArrayList object
		al.add("Sundar Pichai");
		al.add("Satya Nadella");  
		al.add("Shiv Nadar");  
		al.add("Shantanu Narayen");
		al.add("Sundar Pichai");
		al.add("Francisco D’Souza");

		System.out.println("Iterating ArrayList values\n");

		// Iterating using enhanced for-loop
		for(String str : al){

		// removing element at 4th index

		// to print all values of ArrayList
		System.out.println("\n\nArrayList values after"
				+ " removal at 4th index postion \n\n" + al);


Iterating ArrayList values

Sundar Pichai
Satya Nadella
Shiv Nadar
Shantanu Narayen
Sundar Pichai
Francisco D’Souza

ArrayList values after removal at 4th index postion 

[Sundar Pichai, Satya Nadella, Shiv Nadar, 
Shantanu Narayen, Francisco D’Souza]


Note: All methods of ArrayList is non-synchronized but it can be easily converted into synchronized ArrayList using utility method of java.util.Collections class

List list = Collections.synchronizedList(al);




Happy Coding !!
Happy Learning !!