Testing Program

Here is a tiny program that tests the classes. If you want to run the program, copy and paste all the classes and the interface to a file called Store.java.

public class Store
{

  public static void main ( String[] args )
  {
    Goods gd = new Goods( "bubble bath", 1.40 );
    Food  fd = new Food ( "ox tails", 4.45, 1500 );
    Book  bk = new Book ( "Emma", 24.95, "Austin" );
    Toy   ty = new Toy  ( "Legos", 54.45, 8 );

    gd.display();

    fd.display();

    ty.display();
    System.out.println("Tax is: " + ty.calculateTax() + "\n" );

    bk.display();
    System.out.println("Tax is: " + bk.calculateTax() + "\n" );

  }
}

The calculateTax() method is only used with objects whose class implements the interface Here is a picture that shows the classes and their objects:

In the picture, clouds represent classes. Arrows with pointed head connect child classes to parent classes. The dotted rectangle represents the interface; a dotted arrow shows which classes implement it. Rectangles represent objects. Arrows with square head connect an object to its class.