INHERITANCE AND POLYMORPHISM - Introduction to Java Programming - page 412

this .radius = radius;
this .color = color; // Illegal
this .filled = filled; // Illegal

}

This is wrong, because the private data fields color and filled in the
GeometricObject class cannot be accessed in any class other than in the
GeometricObject class itself. The only way to read and modify color and filled is
through their get and set methods.
The Rectangle class (Listing 11.3) extends the GeometricObject class (Listing 11.1)
using the following syntax:

Superclass

Subclass

public class Rectangle

extends GeometricObject

The keyword extends (lines 1-2) tells the compiler that the Rectangle class extends the
GeometricObject class, thus inheriting the methods getColor , setColor , isFilled ,
setFilled , and toString .

L ISTING 11.3 RectangleFromSimpleGeometricObject.java
1 public class RectangleFromSimpleGeometricObject
2
3

extends superclass
data fields

extends SimpleGeometricObject {

private double width;

4 private double height;

5
6 public RectangleFromSimpleGeometricObject() {
7 }
8
9

constructor

public RectangleFromSimpleGeometricObject(

10 double width, double height) {

11 this .width = width;

12 this .height = height;

13 }
14
15 public RectangleFromSimpleGeometricObject(
16 double width, double height, String color, boolean filled) {
17 this .width = width;
18 this .height = height;
19 setColor(color);
20 setFilled(filled);
21 }
22
23 /** Return width */

24 public double getWidth() { methods

25 return width;

26 }
27
28 /** Set a new width */

29 public void setWidth( double width) {

30 this .width = width;

31 }
32