Introduction

• ArrayList is an implemented class of List interface.
• It is present in the java.util package.
• It was introduced in JDK 1.2 version.

• Hierarchy:
  • 

• Syntax :-

  package java.util;
  
  public class ArrayList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable
  {    
      // Constructors
      
      // Methods
      
      // Fields
  }

  • ArrayList implements the RandomAccess marker interface to indicate efficient indexed access.
  • It provides fast random access using get(index) due to the underlying array structure.

• ArrayList is a resizable (dynamic) array in Java that can grow or shrink in size automatically.
  
  

Constructors of ArrayList Class

• Below are the constructors defined in the ArrayList class:

Methods of ArrayList Class

• Below are the methods defined specifically in the ArrayList class:

Program :

• In below program, we are directly using ArrayList class.

• import java.util.ArrayList;
  
  public class ArrayListDemo
  {
      public static void main(String[] args)
      {
          ArrayList<String> list = new ArrayList<>();
  
          // Adding elements
          list.add("Apple");
          list.add("Banana");
          list.add("Mango");
          list.add("Banana"); // duplicate allowed
  
          System.out.println(list);
  
          System.out.println("-------------------------");
  
          // Accessing element
          System.out.println("Element at index 2: " + list.get(2));
  
          System.out.println("-------------------------");
  
          // Updating element
          list.set(1, "Orange");
          System.out.println(list);
  
          System.out.println("-------------------------");
  
          // Removing element
          list.remove("Apple");
          System.out.println(list);
  
          System.out.println("-------------------------");
  
          // Iterating ArrayList
          for(String fruit : list)
          {
              System.out.println(fruit);
          }
      }
  }

  Output:

  [Apple, Banana, Mango, Banana]
  -------------------------
  Element at index 2: Mango
  -------------------------
  [Apple, Orange, Mango, Banana]
  -------------------------
  [Orange, Mango, Banana]
  -------------------------
  Orange
  Mango
  Banana

Properties of ArrayList Class:

1. ArrayList is an index-based data structure, which means the first element is inserted at index 0.
2. ArrayList can store different data types or heterogeneous elements if generics are not used.
3. We can store duplicate elements in the ArrayList.
4. We can store null values in the ArrayList.
5. ArrayList follows the insertion order, meaning elements are retrieved in the same sequence they were added.
6. ArrayList does not follows the sorting order; sorting must be done explicitly using Collections.sort() or list.sort().
7. ArrayList is non-synchronized; not thread-safe for concurrent modifications.
8. ArrayList does not guarantee for data consistency.