Array List in Java

What is Array List ?

• The ArrayList class extends AbstractList and implements the List interface.

• It is resizable array or growable array

• Duplicates are allowed

• Insertion order is preserved

• Supports heterogeneous objects(different type of objects)

• null insertion allowed (al.add(null))  //where al ---> arraylist

• Usually we use collections to hold and transfer objects from 1 location to another location(container) to provide support for these requirements,every collection class by default implements serializable and cloneable interfaces

Constructors::

1) ArrayList l=new ArrayList(); # creates an empty arraylist object with default initial capacity 10.Once arraylist reaches its max. capacity then a New Arraylist object created with 
//New capacity= [current capacity * (3/2)]+1;

2) ArrayList l=new ArrayList(int initialcapacity);  # create an empty arraylist with specified initial capacity.

3) ArrayList l=new ArrayList(Collection c);  # create an equivalent arraylist object for the given collection.

##sample demo program ###

import java.util.ArrayList;

public class ArrayListDemo {

public static void main(String[] args) {

ArrayList al= new ArrayList<>();
al.add(1);
al.add("string type");
al.add(1.2f);
al.add(null);
System.out.println("ArrayList elements ::"+ al);
System.out.println("ArrayList elements class ::"+ al.getClass());
System.out.println("Retrive element from ArrayList :"+al.get(1));
}

}

output:

ArrayList elements ::[1, string type, 1.2, null]
ArrayList elements class ::class java.util.ArrayList

Retrive element from ArrayList :string type

Key Points:

• ArrayList is the best choice if ever frequent operation is retrieval operation(because arraylist implements randomaccess interface)
• ArrayList is the worst choice if ever frequent operation is insertion or deletion in the middle

Please comment below to feedback or ask questions.