Example for the design of a class

Specification: Realize a Java class for representing cars. The properties of interest for a car are the plate number, the model, the color, and the person who owns the car. The first two properties cannot be modified, while the third and fourth can. A car has initially no owner. The owner is assigned to a car only later (e.g., when the car is sold).

By analyzing the above specification, we see that we have to realize a class Car, whose functionalities are:

• creating an object of the class with the properties plate, model, and color initialized to suitable values, and no owner;
• returning the value of each of the properties plate, model, color, and owner;
• changing the color or the owner.

At this point we are ready to write:

public class Car {
  // private representation of the objects: instance variables
  // public methods realizing the requested functionalities
}