Adding the Interface

The child class Food extends the parent class. It uses super to use the parent's constructor and the parent's display method.

class Food extends Goods
{
  double calories;

  Food( String des, double pr, double cal)
  {
    super( des, pr );
    calories = cal ;
  }

  void display()
  {
    super.display( );
    System.out.println( "calories: " + calories );
  }
}

Here is Taxable:

• A Taxable item,
  • has a taxRate of 6 percent, which should be a double constant.
  • and a calculateTax() method. which should return a double value.

The Taxable interface looks like this:

interface Taxable
{
  final double _____ = ______ ;
  double ___________() ;
}

The final says that what follows is a constant, not a variable (variables are not allowed in interfaces.) In fact, the final can be omitted since the identifier that follows will automatically be a constant. The " = value " cannot be omitted.

The method declaration (in the second line) is public by default.