ArrayLists - Building Java Programs: A Back to Basics Approach - page 627

parameterized methods. Remember from Chapter 3 that you can use a parameter to
define a family of related tasks that differ just by a particular characteristic like
height or width. In this case, the parameter is a type and it is used to declare another
type. The type ArrayList<E> represents a family of types that differ just by the
type of element they store. You would use ArrayList<String> to store a list of
String s, ArrayList<Point> to store a list of Point s, ArrayList<Color> to store
a list of Color s, and so on. Notice that you would never actually declare something
to be of type ArrayList<E> . As with any parameter, you have to replace the E with
a specific value to make it clear which of the many possible ArrayList types you
are using.

Basic ArrayList Operations
The ArrayList class is part of the java.util package, so to include it in a program
you must include an import declaration. The syntax for constructing an ArrayList is
more complicated than what we've seen before because of the type parameter. For
example, you would construct an ArrayList of String s as follows:

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

This code constructs an empty ArrayList<String> . This syntax is complicated,
but it will be easier to remember if you keep in mind that the <String> notation is
actually part of the type: This isn't simply an ArrayList , it is an ArrayList<String>
(often read as “an ArrayList of String ”). Notice how the type appears when you
declare the variable and when you call the constructor:

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

type type

If you think in terms of the type being ArrayList<String> , you'll see that
this line of code isn't all that different from the code used to construct an object
like a Point :

Point p = new Point();

type type

Once you've constructed an ArrayList , you can add values to it by calling the
add method:

ArrayList<String> list = new ArrayList<String>();
list.add("Tool");
list.add("Phish");
list.add("Pink Floyd");