Concept explainers
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;
}
}
- a) Which class is the superclass? Which class is the subclass?
- b) Draw a UML diagram showing the relationship between these two classes.
- c) When a Circle object is created, what are its public members?
- d) What members of the Shape class are not accessible to the Circle class’s methods?
- 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());
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