Is each of the classes Toy and Book Taxable?

A good answer might be:

Yes.

An interface can be used as a data type for a reference variable. Since Toy and Book implement Taxable, they can both be used with a reference variable of type Taxable:

public static void main ( String[] args ) { Taxable item1 = new Book ( "Emma", 24.95, "Austin" ); Taxable item2 = new Toy ( "Leggos", 54.45, 8 ); System.out.println( "Tax on item 1 "+ item1.calculateTax() ); System.out.println( "Tax on item 2 "+ item2.calculateTax() ); }

The compiler has been told in the interface that all Taxable objects will have a calculateTax() method, so that method can be used with the variables.

QUESTION 15:

Would the following work?

item1.display() ;