Chapter 9.1, Problem 9.2CP

Look at the following class declarations and answer the questions that follow them:

  public class Shape

  {

    private double area;

    public void setArea(double a)

    {

      area = a;

    }

    public double getArea( )

    {

      return area;

    }

   }

   public class Circle extends Shape

   {

    private double radius;

    public void setRadius(double r)

    {

      radius = r;

      setArea(Math.PI * r * r);

    }

    public double getRadius()

    {

      return radius;

    }

   }

1. a) Which class is the superclass? Which class is the subclass?
2. b) Draw a UML diagram showing the relationship between these two classes.
3. c) When a Circle object is created, what are its public members?
4. d) What members of the Shape class are not accessible to the Circle class’s methods?
5. e) Assume a program has the following declarations:

  Shape s = new Shape();

  Circle c = new Circle();

  Indicate whether the following statements are legal or illegal:

  c. setRadius(10.0);

  s.setRadius(10.0);

  System.out.println(c.getArea());

  System.out.println(s.getArea());