Java How to Program Fourth Edition - DCC

Chapter 9 Object-Oriented Programming 489
Class Circle (Fig. 9.24) is derived from Point. A Circle has a volume of 0.0, so
superclass method volume is not overridden—it is inherited from class Point, which
inherited it from Shape. A Circle has an area different from that of a Point, so the
area method is overridden. Method getName is an implementation of the abstract
method in the superclass. If this method is not overridden here, the Point version of get-
Name would be inherited. Other methods include setRadius to assign a new radius
to a Circle and getRadius to return the radius of a Circle.
1 // Fig. 9.24: Circle.java
2 // Definition of class Circle
3
4 public class Circle extends Point { // inherits from Point
5 protected double radius;
6
7 // no-argument constructor
8 public Circle()
9 {
10 // implicit call to superclass constructor here
11 setRadius( 0 );
12 }
13
14 // constructor
15 public Circle( double circleRadius, int xCoordinate,
16 int yCoordinate )
17 {
18 // call superclass constructor
19 super( xCoordinate, yCoordinate );
20
21 setRadius( circleRadius );
22 }
23
24 // set radius of Circle
25 public void setRadius( double circleRadius )
26 {
27 radius = ( circleRadius >= 0 ? circleRadius : 0 );
28 }
29
30 // get radius of Circle
31 public double getRadius()
32 {
33 return radius;
34 }
35
36 // calculate area of Circle
37 public double area()
38 {
39 return Math.PI * radius * radius;
40 }
41
Fig. Fig. Fig. 9.24 9.24 9.24 Circle subclass of Point—indirect subclass of abstract class
Shape (part 1 of 2).
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