Example for the design of a class: a client

Let us realize a client, CarServices, of the class Car. The class CarServices contains two static methods:

• spray, which takes as parameters (a reference to) an object Car and (a reference to) an object String, representing the (new) color of the car, and modifies the object Car by changing its color;
• registerAlfa147, which takes as parameters two objects String that represent respectively the plate and the color and returns (a reference to) a new object Car whose model is "Alfa147" and whose plate and color are specified by the parameters.

We write the class CarServices, in a file called CarServices.java, as follows:

public class CarServices {
  public static void spray(Car car, String color) {
    car.setColor(color);
  }
  public static Car registerAlfa147(String pla, String col) {
    return new Car(pla, "Alfa147", col);
  }
}

Finally, we realize a class Main, containing a method main, that uses the class Car and the class CarServices. This class will be written in a separate file Main.java:

public class Main {

  // auxiliary method
  private static void printCarData(Car a) {
    System.out.println("Car: " + a.getPlate() + ", "
                               + a.getModel()+ ", "
                               + a.getColor());
  }

  // auxiliary method
  private static void printOwnerData(Car a) {
    System.out.println("Owner: " + a.getOwner().getName() + ", "
                                 + a.getOwner().getResidence());
  }

  public static void main(String[] args) {
    Car a = new Car("313","Fiat 500","Red and Blu");
    printCarData(a);
    Person p = new Person("Paperino", "Paperopoli");
    a.setOwner(p);
    printOwnerData(a);
    CarServices.spray(a, "Maranello Red");
    printCarData(a);
    Car b = CarServices.registerAlfa147("131", "Alfa Red");
    printCarData(b);
    Person c = new Person("Clarabella", "Topolinia");
    b.setOwner(c);
    printOwnerData(b);
  }
}