INHERITANCE AND POLYMORPHISM - Introduction to Java Programming - page 411

16 setFilled(filled);
17 }
18
19 /** Return radius */

20 public double getRadius() { methods

21 return radius;

22 }
23
24

/** Set a new radius */

25 public void setRadius( double radius) {

26 this .radius = radius;

27 }
28
29 /** Return area */

30 public double getArea() {

31 return radius * radius * Math.PI;

32 }
33
34

/** Return diameter */

35 public double getDiameter() {

36 return 2 * radius;

37 }
38
39 /** Return perimeter */

40 public double getPerimeter() {

41 return 2 * radius * Math.PI;

42 }
43
44 /** Print the circle info */
45 public void printCircle() {
46 System.out.println( "The circle is created " + getDateCreated() +

47 " and the radius is " + radius);

48 }
49 }

The Circle class (Listing 11.2) extends the GeometricObject class (Listing 11.1) using
the following syntax:

Superclass

Subclass

public class Circle

extends GeometricObject

The keyword extends (lines 1-2) tells the compiler that the Circle class extends the
GeometricObject class, thus inheriting the methods getColor , setColor , isFilled ,
setFilled , and toString .
The overloaded constructor Circle(double radius, String color, boolean
filled) is implemented by invoking the setColor and setFilled methods to set the
color and filled properties (lines 12-17). These two public methods are defined in the base
class GeometricObject and are inherited in Circle , so they can be used in the derived
class.
You might attempt to use the data fields color and filled directly in the constructor as
follows:

private member in base class

public CircleFromSimpleGeometricObject(
double radius, String color, boolean filled) {