ArrayList

1. What is ArrayList?

ArrayList is one of the most commonly used implementations of the List interface. It stores elements in a resizable array internally, growing automatically as more elements are added.

2. Why is it used?

Unlike a normal array, ArrayList can grow or shrink as needed, and it comes with many built-in methods for adding, removing, and searching elements, making everyday list operations much simpler.

3. Real-Life Example

Think of an expandable file folder that automatically adds more sections as you keep adding documents, instead of being limited to a fixed number of sections from the start.

4. Syntax

java
ArrayList<DataType> listName = new ArrayList<>();

5. Example Program

java
import java.util.ArrayList;

public class ArrayListDemo {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<>();
        numbers.add(10);
        numbers.add(20);
        numbers.remove(0);
        System.out.println(numbers);
    }
}

Output:

[20]

6. Key Points to Remember

• ArrayList is best when frequent reading/searching is needed, since it offers fast index-based access.
• Adding or removing elements from the middle of a large ArrayList can be slower, since remaining elements need to shift.
• ArrayList is not synchronized, so it is not automatically safe to use across multiple threads at once.