And the list goes on and on and on….

Advantages of a List Like an array, a List is set up to store multiple items. But it has several advantages: It can be dynamically expanded to make room for more items. Items can be removed and inserted anywhere with ease. It has several other methods such as contains which gives it much more utility than an array. The one disadvantage is that it can not store primitives. But there is a work around to this which we will cover latter.

Design of a List There are several ways that Lists are set up such. There are ArrayLists, LinkedLists, Stack, Vector, etc. Each implementation has the same interface. But encapsulation allows us to have different implementations.

ArrayList The one specific type of list that we will be using will be an ArrayList. It’s implementation includes using an array inside the ArrayList class. But things like expanding the ArrayList, adding items in order, and other things are taken care of for us inside the ArrayList class. Encapsulation for the win!

Adding and Removing at an index Given the following items were in an ArrayList called letters: {“A”, “B”, “C”, “D”, “E”, “F”} This is how the ArrayList would change after the following method calls: letters.add(“X”); {“A”, “B”, “C”, “D”, “E”, “F”, “X”} letters.add(1, “Y”); {“A”, “Y”, “B”, “C”, “D”, “E”, “F”, “X”} letters.remove(4); {“A”, “Y”, “B”, “C”, “E”, “F”, “X”} letters.set(0, “Z”); {“Z”, “Y”, “B”, “C”, “E”, “F”, “X”}

A collection of objects Lists by default are designed to store any object. This allows you to add an object of any type to a list. But this can be problematic since you can not be certain of the type of the object that you obtain from the list. Think of it like having a big box that you can put all different types of household items into. It is convenient to do so until you want a hammer and you pull out a scarf.

Declaring it with a type You can restrict the type of objects that a list stores in the following manner Declared without a type: ArrayList carLot = new ArrayList(); carLot.add(new Car(“Camry”)); carLot.add(new Toy(“Elmo”)); ((Car)carLot.get(0)).run(); Declared with a type: ArrayList<Car> carLot = new ArrayList<Car>(); carLost.get(0).run(); In the second example, only Car objects can be added to the list and you don’t have to cast objects returned from the list as a Car to call Car methods