Classes - Building Java Programs: A Back to Basics Approach - page 506

25 // translate each point to a new location
26 p1.x += 11;
27 p1.y += 6;
28 p2.x += 1;
29 p2.y += 7;
30
31 // print the points again
32 System.out.println("p1 is (" + p1.x + ", " + p1.y + ")");
33 System.out.println("p2 is (" + p2.x + ", " + p2.y + ")");
34 }
35 }
The code produces the following output:
p1 is (7, 2)
distance from origin = 7.280109889280518
p2 is (4, 3)
distance from origin = 5.0
p1 is (18, 8)
p2 is (5, 10)
The client program has some redundancy that we'll eliminate as we improve our
Point class in the sections that follow.
Our initial Point class essentially serves as a way to group two int values into
one object. This technique is somewhat useful for the client program, but the client
could have been written using primitive int s instead. Using Point objects is not yet
substantially better than using primitive int values, because our Point objects do
not yet have any behavior. An object that contains state, but no behavior, is some-
times called a record or struct. In the sections that follow, we'll grow our Point class
from a minimal implementation into a proper Java class.
Object Behavior: Methods
The second version of our Point class will contain both state and behavior. Behavior
of objects is specified by writing instance methods. The instance methods of an
object describe the messages to which that object can respond.
Instance Method
A method inside an object that operates on that object.
The objects introduced in previous chapters all contained instance methods that
represented their behavior. For example, a String object has a length method and a
Scanner object has a nextInt method. We think of these methods as being stored