ArrayList in Java

An ArrayList in Java is a part of the Java Collections Framework and provides a dynamic array for storing elements. Unlike arrays in Java, which have a fixed size, an ArrayList can grow and shrink in size dynamically when elements are added or removed.

Key Features of ArrayList in Java

• Resizable: Automatically resizes as elements are added or removed.
• Indexed Access: Allows random access of elements using an index.
• Non-synchronized: Not thread-safe, but can be synchronized externally.
• Allows Duplicates: Can store duplicate elements.

Basic Operations

• Adding elements: add()
• Accessing elements: get()
• Modifying elements: set()
• Removing elements: remove()
• Size of the list: size()

Example of Using ArrayList in Java

import java.util.ArrayList;

public class ArrayListExample {
    public static void main(String[] args) {
        // Creating an ArrayList of String type
        ArrayList<String> fruits = new ArrayList<>();

        // Adding elements to the ArrayList
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");
        System.out.println("Initial ArrayList: " + fruits);

        // Accessing elements
        System.out.println("Element at index 1: " + fruits.get(1));

        // Modifying elements
        fruits.set(1, "Blueberry");
        System.out.println("ArrayList after modification: " + fruits);

        // Removing elements
        fruits.remove(2);
        System.out.println("ArrayList after removal: " + fruits);

        // Size of the ArrayList
        System.out.println("Size of the ArrayList: " + fruits.size());
    }
}

Output:

Initial ArrayList: [Apple, Banana, Cherry]
Element at index 1: Banana
ArrayList after modification: [Apple, Blueberry, Cherry]
ArrayList after removal: [Apple, Blueberry]
Size of the ArrayList: 2

Explanation

Creating an ArrayList in Java:

ArrayList<String> fruits = new ArrayList<>();

This line creates an ArrayList of type String.

Adding elements:

fruits.add("Apple");
fruits.add("Banana");
fruits.add("Cherry");

Elements “Apple”, “Banana”, and “Cherry” are added to the ArrayList.

Accessing elements:

System.out.println("Element at index 1: " + fruits.get(1));

Retrieves the element at index 1, which is “Banana”.

Modifying elements:

fruits.set(1, "Blueberry");

Replaces the element at index 1 (“Banana”) with “Blueberry”.

Removing elements:

fruits.remove(2);

Removes the element at index 2 (“Cherry”).

Size of the ArrayList in Java:

System.out.println("Size of the ArrayList: " + fruits.size());

Prints the size of the ArrayList, which is 2 after removal.

Summary

An ArrayList in Java is a flexible and powerful data structure for storing and manipulating a dynamically sized collection of elements. It provides various methods to perform different operations like adding, removing, and accessing elements efficiently.