1. Java’s World in UML Object Shape {abstract} This is done implicitly
ShapeName: String
# setShapeName(newShapeName: String): void
+ getShapeName(): String
+ draw(Graphics g):void
+ erase(Graphics g):void
+ getSurfaceArea(): double
+ getPerimeter(): double
There are some details that are not as important to the concept of shape, hence leave them for the programmer to implement.
7/24/2018
IT 179

2. Java’s World in UML Object Shape {abstract} Rectangle Circle ThreeD
This is done
implicitly
Shape
{abstract}
extends
Rectangle
Circle
ThreeD
{interface}
RectanglePrism
Cylinder
implements
7/24/2018
IT 179

3. Shape package shapes; public abstract class Shape {
protected static final double DEFAULT_SIZE = ( double ) 1.0;
protected static final String DEFAULT_NAME = "Unknown";
private String shapeName;
public Shape() {
this.shapeName = DEFAULT_NAME; }
public Shape( String name ) {
setShapeName( name );
protected void setShapeName( String name ) {
shapeName = new String( name );
public abstract double getSurfaceArea();
……………………………
7/24/2018
IT 179

4. Java’s World in UML Object Shape {abstract} Circle Rectangle
This is done
implicitly
Shape
{abstract}
extends
Circle
Rectangle
7/24/2018
IT 179

5. Shape {abstract} Rectangle Circle
ShapeName: String
# setShapeName(newShapeName: String): void
+ getShapeName(): String
+ draw(Graphics g):void
+ erase(Graphics g):void
+ getSurfaceArea(): double
+ getPerimeter(): double
Rectangle
length: double
height: double
+ setLength(newLength: double): void
+ getLength(): double
+ setHeight(newHeight: double): void
+ getHeight(): double
Circle
radius: double
+ setRadius(newRadius: double): void
+ getRadius(): double
7/24/2018
IT 179

6. public class Circle extends Shape { private double radius;
package shapes;
public class Circle extends Shape {
private double radius;
public Circle() {
super( "Circle" );
setRadius( super.DEFAULT_SIZE ); }
public Circle( double theRadius ) {
if ( theRadius <= 0.0 ) {
setRadius( Shape.DEFAULT_SIZE );
else {
setRadius( theRadius );
......
7/24/2018
IT 179

7. public class Circle extends Shape { private double radius; .....
package shapes;
public class Circle extends Shape {
private double radius;
.....
public double getRadius() {
return this.radius; }
public void setRadius( double theRadius ) {
if ( theRadius <= 0 ) {
return;
this.radius = theRadius;
public double getSurfaceArea() {
return this.radius * this.radius * Math.PI;
public double getPerimeter() {
return 2 * this.radius + Math.PI;
7/24/2018
IT 179

8. Extend to three-dimension
Shape
{abstract}
Rectangle
Circle
RectanglePrism
z: double
+ setZ(double): void
+ getZ(): double
+ getVolume(): double
RectanglePrism
Cylinder
depth: double
+ setDepth(double): void
+ getDepth(): double
+ getCapacity(): double
Cylinder
7/24/2018
IT 179

9. Java’s World in UML Object Shape {abstract} Rectangle Circle
extends
RectanglePrism
Cylinder
7/24/2018
IT 179

10. Is there an even better way?
public double price(Cylinder k, double unitPrice) {
return k.getCapacity()*unitPrice; }
public double price(RectanglePrism k, double unitPrice) {
return k.getVolume()*unitPrice;
overloading
What’s the problem?
Is there a better way?
/* Supposed that getVolumn is defined in Shape */
public double price(Shape k, double unitPrice) {
return k.getVolume()*unitPrice; }
Is there an even better way?
Yes, we use “interface”.
How to unify the interface?
7/24/2018
IT 179

11. Java’s World in UML Object Shape {abstract} Rectangle Circle ThreeD
This is done
implicitly
Shape
{abstract}
extends
Rectangle
Circle
ThreeD
{interface}
RectanglePrism
Cylinder
implements
7/24/2018
IT 179

12. interface Object Shape {abstract} Rectangle Circle RectanglePrism
ThreeD
{interface}
+ setDepth(double): void
+ getDepth(): double
+ getVolume(): double
Rectangle
Circle
RectanglePrism
Cylinder
implements
7/24/2018
IT 179

13. polymorphism public double price(ThreeD k, double unitPrice) {
return k.getVolum()*unitPrice; }
polymorphism
public static void main(String[] args) {
Rectangle a;
Circle b;
RectanglePrism c;
Cylinder d;
… … …
price(c,2.99)+price(d,3.99);
// price(a,2.99)+price(b,3.99); Not allowed
7/24/2018
IT 179

14. ThreeD must be all abstract
package shapes;
public interface ThreeD {
double getDepth();
void setDepth( double theDepth );
double getVolume(); }
must be all abstract
Any class implements the interface must implement all
methods in the interface.
Some interfaces don’t even have the body
called marker interface.
7/24/2018
IT 179

15. Cylinder (I) package shapes;
public final class Cylinder extends Circle implements ThreeD {
private double depth;
public Cylinder() {
this( Shape.DEFAULT_SIZE, Shape.DEFAULT_SIZE ); }
public Cylinder( double theRadius, double theWidth ) {
setShapeName( "Cylinder" );
if ( theRadius <= 0.0 ) {
setRadius( Shape.DEFAULT_SIZE );
else {
setRadius( theRadius );
if ( theWidth <= 0.0 ) {
setDepth( Shape.DEFAULT_SIZE );
setDepth( theWidth );
....
7/24/2018
IT 179

16. Object’s toString and equals methods
+ toString(): String
+ equals(o: Object): boolean
the default method
use identities to do the job.
Shape
{abstract}
Now, we have a better idea about how this job to be done.
Rectangle
Circle
7/24/2018
IT 179

17. Rectangle Don’t make it Rectangle
package shapes;
public class Rectangle extends Shape {
....
public String toString() {
return this.getShapeName() + ": length = " + this.length
+ ", height = " + this.height; }
public boolean equals( Object o ) {
if ( ( o == null ) || ( ! ( o instanceof Rectangle ) ) ) {
return false;
return ( ( ( ( Rectangle ) o ).getLength() == getLength() ) &&
( ( ( Rectangle ) o ).getHeight() == getHeight() ) );
.....
Don’t make it Rectangle
So, this method can take any object of any class.
7/24/2018
IT 179

18. r1 r2 c rp1 rp2 cd1 cd2 7/24/2018 IT 179 import shapes.*;
public static void main(String[] args) {
Rectangle r1 = new Rectangle(2,1);
Rectangle r2 = new Rectangle(3,2);
Circle c = new Circle(0.7);
RectanglePrism rp1 =
new RectanglePrism(1,1.5,1.3);
RetanglePrime rp2 = ... ;
Cylinder cd1 = ... ,cd2 = ... ;
... }
length = 1
height = 1.5
z =1.3
getSurfaceArea() {…}
getVolumn)_ {…} ….
length = 2
height = 1
getSurfaceArea() {…} ….
length = 3
height = 2
getSurfaceArea() {…} …. r1 r2 c
rp1
rp2
cd1
cd2
radius = 0.7
getSurfaceArea() {…} ….
length = 1.6
height = 3
z =1.6
getSurfaceArea() {…}
getVolumn)_ {…} ….
radius = 1.5
depth = 3
getSurfaceArea() {…}
getVolumn)_ {…} ….
radius = 1
depth = 2
getSurfaceArea() {…}
getVolumn)_ {…} ….
7/24/2018
IT 179

19. Visibility Access Levels Modifier Class Package Subclass
Every one in the World
public Y
protected N
no modifier
private
7/24/2018
IT 179

20. Comparable<T> {interface}
Object
Comparable<T> {interface}
+ compareTo(o:T): int
Shape
{abstract}
ThreeD
{interface}
+ setDepth(double): void
+ getDepth(): double
+ getVolume(): double
Rectangle
Circle
RectanglePrism
Cylinder
7/24/2018
IT 179