How to Find Size of ArrayList in Java - Simple Guide

To find the size of an ArrayList in Java, use the size() method. It returns the number of elements currently stored in the list as an int value.

Syntax

The syntax to get the size of an ArrayList is simple:

• arrayList.size() - calls the size() method on the ArrayList object.
• This method returns an int representing the number of elements in the list.

java

int size = arrayList.size();

Example

This example creates an ArrayList of strings, adds some items, and prints the size using size().

java

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");

        int size = fruits.size();
        System.out.println("Number of fruits: " + size);
    }
}

Output

Number of fruits: 3

Common Pitfalls

Some common mistakes when finding the size of an ArrayList include:

• Using length instead of size(). length is for arrays, not ArrayList.
• Calling size() on a null reference causes a NullPointerException.
• Expecting size() to return capacity instead of the actual number of elements.

java

/* Wrong: Using length on ArrayList */
// int size = arrayList.length; // This causes a compile error

/* Correct: Use size() method */
int size = arrayList.size();

Quick Reference

Remember these key points:

• size() returns the current number of elements.
• It does not return the capacity of the list.
• Always ensure the ArrayList is not null before calling size().

Key Takeaways

Use the size() method to get the number of elements in an ArrayList.

Do not use length with ArrayList; it is for arrays only.

Calling size() on a null ArrayList causes an error.

size() returns the count of elements, not the capacity.

Always check your ArrayList is initialized before calling size().