A case study - Objects First with Java: A Practical Introduction Using BlueJ - page 497

Figure 14.2
A visualization of
the city
■ A Simulation class now manages the actors, much as it did in the foxes-and-rabbits
project . The actors are the vehicles, the passenger source, and a GUI provided by the
CityGUI class. After each step, the simulation pauses for a brief period so that the GUI does
not change too quickly.
■ The need for something like the City class was identified during development of stage one.
The City object defines the dimensions of the city's grid and holds a collection of all the
items of interest that are in the city—the vehicles and the passengers.
■ Items in the city may optionally implement the DrawableItem interface, which allows
the GUI to display them. Images of vehicles and people are provided in the images folder
within the project folder for this purpose.
■ The Taxi class implements the DrawableItem interface. It returns alternative images to the
GUI, depending on whether it is occupied or empty. Image files exist in the images folder
for a shuttle to do the same.
■ The PassengerSource class has been refactored significantly from the previous version, to
better fit its role as an actor. In addition, it maintains a count of missed pickups for statistical
analysis.
■ The TaxiCompany class is responsible for creating the taxis to be used in the simulation.
As you explore the source code of the taxi-company-later-stage project, you will find illus-
trations of many of the topics we have covered in the second half of this topic: inheritance,
polymorphism, abstract classes, interfaces, and error handling.