// Setter method for width
public void setWidth(double width) {
this.width = width; }
// Getter method for height public double getHeight() {
return height; }
// Setter method for height
public void setHeight(double height) {
this.height = height; }
// Implement the findArea method in GeometricObject public double findArea() {
return width*height; }
// Implement the findPerimeter method in GeometricObject public double findPerimeter() {
return 2*(width + height); }
// Override the equals() method defined in the Object class public boolean equals(Rectangle rectangle) {
return (width == rectangle.getWidth()) && (height == rectangle.getHeight()); }
// Override the toString() method defined in the Object class public String toString() {
return \ } }
4、使用Windows写字板编辑类TestPolymorphism，源代码如下： public class TestPolymorphism {
// Main method
public static void main(String[] args) {
// Declare and initialize two geometric objects GeometricObject geoObject1 = new Circle(5);
GeometricObject geoObject2 = new Rectangle(5, 3);
System.out.println(\ equalArea(geoObject1, geoObject2));
// Display circle
displayGeometricObject(geoObject1);
// Display rectangle
displayGeometricObject(geoObject2); }
// A method for comparing the areas of two geometric objects static boolean equalArea(GeometricObject object1, GeometricObject object2) {
return object1.findArea() == object2.findArea(); }
// A method for displaying a geometric object
static void displayGeometricObject(GeometricObject object) {
System.out.println();
System.out.println(object.toString());
System.out.println(\
System.out.println(\ } }
5、把上面编辑的几个源程序保存成Java源程序文件(扩展名为java)，程序
文件名分别为GeometricObject.java、Circle.java、Rectangle.java、TestPolymorphism.java。
6、进入命令提示符状态，在源程序文件存放目录下对以上文件进行编译。
观察编译后源程序文件存放目录中的文件，熟悉Java程序的文件结构。 7、如果编译正确，则键入如下命令行，使用Java解释器运行源程序：
java TestPolymorphism
程序运行结果如下：
8、使用Windows写字板编辑编辑类TestInterface源程序如下： public class TestInterface {
// Main method
public static void main(String[] args) {
// Create two comarable circles
ComparableCircle circle1 = new ComparableCircle(5); ComparableCircle circle2 = new ComparableCircle(4);
// Display the max circle
Comparable circle = Max.max(circle1, circle2); System.out.println(\ ((Circle)circle).getRadius()); System.out.println(circle);
// Create two comarable cylinders
ComparableCylinder cylinder1 = new ComparableCylinder(5, 2); ComparableCylinder cylinder2 = new ComparableCylinder(4, 5);
// Display the max cylinder
Comparable cylinder = Max.max(cylinder1, cylinder2); System.out.println();
System.out.println(\ cylinder1.findVolume());
System.out.println(\ cylinder2.findVolume());
System.out.println(\
((Cylinder)cylinder).getRadius() + \ ((Cylinder)cylinder).getLength() + \ ((Cylinder)cylinder).findVolume()); System.out.println(cylinder); } }
// ComparableCircle is a subclass of Circle, which implements the // Comparable interface
class ComparableCircle extends Circle implements Comparable {
// Construct a CompareCircle with specified radius public ComparableCircle(double r) {
super(r); }
// Implement the compareTo method defined in Comparable public int compareTo(Object o) {
if (getRadius() > ((Circle)o).getRadius()) return 1;
else if (getRadius() < ((Circle)o).getRadius()) return -1; else
return 0; } }
// ComparableCylinder is a subclass of Cylinder, which implements the // CompareObject interface
class ComparableCylinder extends Cylinder implements Comparable {
// Construct a CompareCylinder with radius and length ComparableCylinder(double r, double l) {
super(r, l); }
// Implement the compareTo method defined in Comparable interface public int compareTo(Object o) {
if (findVolume() > ((Cylinder)o).findVolume()) return 1;
else if (findVolume() < ((Cylinder)o).findVolume()) return -1; else
return 0; } }
10、使用Windows写字板编辑编辑类Circle源程序如下： public class Circle {
protected double radius;
public Circle() {
radius=1.0; }
// Construct circle with specified radius public Circle(double r) {
radius=r; }
// Getter method for radius public double getRadius() {
return radius; }
// Setter method for radius
public void setRadius(double radius) {
this.radius = radius; }
// Implement the findArea method defined in GeometricObject public double findArea() {
return radius*radius*Math.PI; }
public boolean equals(Circle circle) {
return this.radius == circle.getRadius(); }
// Override the toString() method defined in the Object class