Java ArrayList

In Java, we use the ArrayList class to implement the functionality of resizable-arrays.It implements the List interface of the collections framework.

Creating an ArrayList:
Before using ArrayList, we need to import the java.util.ArrayList package first. Here is how we can create arraylists in Java:

ArrayList<Type> arrayList= new ArrayList<>();

Example: Create ArrayList in Java:

import java.util.ArrayList;

class Main {
  public static void main(String[] args){


    // create ArrayList
    ArrayList<String> languages = new ArrayList<>();


    // Add elements to ArrayList
    languages.add("Java");
    languages.add("Python");
    languages.add("Swift");
    System.out.println("ArrayList: " + languages);
  }
}

Output

ArrayList: [Java, Python, Swift]

Basic Operations on ArrayList:

  • Add elements
  • Access elements
  • Change elements
  • Remove elements

Methods of ArrayList Class:

MethodsDescriptions
size()Returns the length of the arraylist.
sort()Sort the arraylist elements.
clone()Creates a new arraylist with the same element, size, and capacity.
contains()Searches the arraylist for the specified element and returns a boolean result.
ensureCapacity()Specifies the total element the arraylist can contain.
isEmpty()Checks if the arraylist is empty.
indexOf()Searches a specified element in an arraylist and returns the index of the element.

The important points about the Java ArrayList class are:

  • Java ArrayList class can contain duplicate elements.
  • Java ArrayList class maintains insertion order.
  • Java ArrayList class is non synchronized.
  • Java ArrayList allows random access because the array works on an index basis.
  • In ArrayList, manipulation is a little bit slower than the LinkedList in Java because a lot of shifting needs to occur if any element is removed from the array list.
  • We can not create an array list of the primitive types, such as int, float, char, etc. It is required to use the required wrapper class in such cases. 
  • Java ArrayList gets initialized by the size. The size is dynamic in the array list, which varies according to the elements getting added or removed from the list.