Let’s say we have an ArrayList that stores items in a user’s online shopping cart. As the user navigates through the site and adds items, their cart grows bigger and bigger.

If we wanted to display the number of items in the cart, we could find the size of it using the size() method:

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

shoppingCart.add("Trench Coat");
System.out.println(shoppingCart.size());
// 1 is printed
shoppingCart.add("Tweed Houndstooth Hat");
System.out.println(shoppingCart.size());
// 2 is printed
shoppingCart.add("Magnifying Glass");
System.out.println(shoppingCart.size());
// 3 is printed

In dynamic objects like ArrayLists, it’s important to know how to access the amount of objects we have stored.