Classes - Building Java Programs: A Back to Basics Approach - page 502

Point Objects
To learn about objects we will first examine an existing Java class, and then we will
reimplement our own version of that class from scratch. The java.awt package has a
class named Point . A Point object stores the ( x, y ) coordinates of a position in two-
dimensional space. These coordinates are expressed as integers, although there are
also variations for storing points using floating-point numbers. Point objects are
useful for applications that store many two-dimensional locations, such as maps of
cities, graphical animations, and games.
Like most objects, Point objects have to be explicitly constructed by calling a
constructor. To construct a specific Point object, you have to pass the values you
want for x and y :

Point p = new Point(3, 8);

After the program executes the previous line of code, you have the following situ-
ation:

p x 3 x 3 y 8

Once you have constructed a Point object, what can you do with it? One of the
most common things you do with an object is print it to the console. A Point object,
like many Java objects, can be printed with the println statement.

System.out.println(p);

The println statement produces the following output. The format is a little ugly,
but it lets you see the x and y values inside a given Point .

java.awt.Point[x=3,y=8]

Point objects also have a method called translate that can be used to shift the
coordinates by a specific delta-x and delta-y, which are passed as parameters. When
you translate a Point , you shift its location by the specified amount. For example,
you might say:

p.translate(-1, -2); // subtract 1 from x, subtract 2 from y

Given that the Point started out with coordinates (3, 8), this translation would
leave the Point with coordinates (2, 6). Thus, after this line of code is executed,
you'd end up with the following situation:

p x 3 x 2 y 6