Software Objects and RealWorld Representations - Programming GPS and OpenStreetMap Applications with Java - page 10

created to instantiate a number of Car s for a simple application. To show
a rectangle (representing a car) moving on a map to display a Car can
be implemented with only a few details or attributes like size,location,
speed and direction . A Car implementation with an internally hidden
wireless connection to a receiver could pick up a real car's live position as
a live reference to the real world! Many Car s in one environment can make
up a simple trac application and can provide some clues to the current
trac situation.
The trac application cannot \see" the actual implementation. It relies
on its interfaces and can not distinguish, if a Car is actually making use of
a live GPS signal or if it is a computer simulation of a car. The application
would have to add plausibility tests to check, if the depicted path is more
or less realistic. We rst check the car's path against a satellite picture to
see if the car is moving on a real road. We then check if the speed of the
car is reasonable. . . , and so on. A car is real as soon as every detail of a
car and its behavior is represented in the software object Car . A Car gets
more realistic with every detail added to the class Car .
LearningtheJavaLanguage>InterfacesandInheritance>Interfaces
. . . Imagine a futuristic society where computer-controlled
robotic cars transport passengers through city streets without
a human operator. Automobile manufacturers write software
(Java, of course) that operates the automobile--stop, start, ac-
celerate, turn left, and so forth.
Another industrial group, electronic-guidance instrument
manufacturers, make computer systems that receive global po-
sitioning satellite (GPS) position data and wireless transmis-
sion of trac conditions and use that information to drive the
car.
The auto manufacturers must publish an industry-
standard interface that spells out in detail what methods can
be invoked to make the car move (any car, from any manufac-
turer). The guidance manufacturers can then write software
that invokes the methods described in the interface to com-
mand the car. Neither industrial group needs to know how
the other group's software is implemented. In fact, each group
considers its software highly proprietary and reserves the right
to modify it at any time, as long as it continues to adhere to
the published interface.
Our approach is comparable to scientific research. No matter what kind
of science or what kind of experiment, all scientists are searching for more
details for the one reality.