Lists of things are common in the real world and in programming. People make lists of things they need to buy and lists of things they need to do. A text editor keeps a list of pages. A test consists of a list of questions.

ArrayList implements the List<E> interface. The List<E> interface captures the idea of a list without saying how the idea is implemented. ArrayList is just one implementation of the idea.

Recall that an interface consists of constants and method declarations. A class that implements an interface must implement each of the methods listed in the interface. There are no constants in List<E>, but there are many methods.

A list is an ordered collection of elements. Duplicate elements are allowed in an ArrayList (and in most other implementations of List<E>). Elements in a list can be accessed by their index, as with an array. There are methods to add elements, get elements, remove elements, and search for elements (and many other methods).

Question 9:
What is the index of the first cell of a list?