Software Objects and RealWorld Representations - Programming GPS and OpenStreetMap Applications with Java - page 5

Object referencing also raises awareness of a very important aspect:
Imagine you and your neighbor have identical TV sets. If you have two pro-
grams (controls) referencing two devices, how do you prevent your neighbor
from changing the state of your TV, for example switching your channels.

1.2.1 A Video Application

In order to set up the programming example, the television will be divided
into components, and three multimedia devices will be added:

ˆ The TV set is composed of

{a screen (the front end),
{a tuner to receive external signals from an antenna, cable, satel-
lite dish, etc.,
{a sound device (amplier and speakers);

ˆ a hard disc to record the signal from the receiver (persistence);

ˆ a DVD burner to record the signal of a selected channel or from the
hard disc and a second tuner to receive additional signals;

ˆ a clock (signal).

(One might consider the clock as a background synchronizer for the actual
devices and in a way, part of the program environment.)

Figure1.2. The java programming environment can control any device as long
as it supplies a java application interface (API). One application can replace all
remote controls, if it can access or reference the individual devices APIs.