1. ITEC324 Principle of CS III
Chapter 4 (Horstmann’s Book)
Interface Types and Polymorphism: Graphics, Timer, Animation
Hwajung Lee
ITEC324 Principle of CS III

2. Why? Interfaces Polymorphism
A class defines a set of operations (the interface) and statements (implementation).
Separating the interface concept from that of a class can help in the development of “generic” reusable code.
Polymorphism
Polymorphism: Ability to select different methods according to actual object type.
Multiple classes can implement the same interface type so that it is possible to operate on a mixture of objects from any of these classes.

3. The Icon Interface Type
public interface Icon { int getIconWidth(); int getIconHeight(); void paintIcon(Component c,
Graphics g,
int x,
int y); }

4. Shape Interface Type & Polymorphism (1)
paintIcon method receives graphics context of type Graphics
Actually a Graphics2D object in modern Java versions
public void paintIcon(Component c, Graphics g, int x, int y) { Graphics2D g2 = (Graphics2D) g; }
Can draw any object that implements Shape interface
Shape s = . . .; g2.draw(s);
The Shape interface provides four groups of overloaded methods that make it possible to perform the following tasks:
Get a bounding box that is guaranteed to enclose a specified Shape object.
Determine if a specified Shape object completely contains a specified point or rectangle.
Determine if a specified Shape intersects a specified rectangle
Get a PathIterator object that can be used to obtain the path that makes up the boundary of a Shape object.

5. Shape Interface Type & Polymorphism (2) Drawing Rectangles and Ellipses
Rectangle2D.Double constructed with 
top left corner
width
height
g2.draw(new Rectangle2D.Double(x, y, width, height));
For Ellipse2D.Double, specify bounding box
Comments from Banton, Christopher
public static class Double extends Rectangle2D implements Serializable { ... } So "Double" is its own class, which is located within the Rectangle2D class for convenience. According to this webpage ( it's called a nested top-level class.

6. Shape Interface Type & Polymorphism (3) Drawing Ellipses

7. Shape Interface Type & Polymorphism (4) Drawing Line Segments
Point2D.Double is a point in the plane
Line2D.Double joins to points
Point2D.Double start = new Point2D.Double(x1, y1); Point2D.Double end = new Point2D.Double(x2, y2); Shape segment = new Line2D.Double(start, end); g2.draw(segment);

8. Shape Interface Type & Polymorphism (5) Relationship btw Shape Interface and Classes

9. Shape Interface Type & Polymorphism (6) Drawing Text
g2.drawString(text, x, y);
x, y are base point coordinates

10. Shape Interface Type & Polymorphism (7) Filling Shapes
Fill interior of shape g2.fill(shape);
Set color for fills or strokes: g2.setColor(Color.red);
Program that draws car Ch4/icon3/CarIcon.java

11. Anonymous Classes
No need to name objects that are used only once. Collections.sort(students, new StudentComparatorByName());
No need to name classes that are used only once.
Comparator<Student> comp = new Comparator<Student>() { public int compare(Student student1, Student student2) {
return student1.getName().compareTo(student2.getName()); } };
References:
Generics in Java
Comparator
Comparable
Comparable vs Comparator

12. Factory Methods Anonymous class is commonly used in factory methods:
public class Student {
public static Comparator<Student> comparatorByName() {    return new Comparator<Student>()    {       public int compare(Student s1, Student s2) { }    };
} }
Neat arrangement if multiple comparators make sense (by name, by grade, ...)
References:
Static

13. User Interface Action (1)
Ch4/action1/ActionTest.java

14. User Interface Action (2) Accessing Variables from Enclosing Scope
Method of Inner classes can access variables that are visible in the enclosing scope
 e.g. actionPerformed method accesses the textField variable of the enclosing main method
If an inner class accesses a local variable from an enclosing scope, the variable must be declared as final.
final JTextField textField = new TextField(Field_WIDTH);

15. User Interface Action (3)
To construct multiple objects of the same anonymous class, you must instantiate the anonymous class in a helper method (a factory method) and then call it multiple times.
Note: you should declare parameters final
Debug the following Code
public static ActionListener createGreetingButtonListener(String message) {
return new ActionListener() { public void actionPerformed(ActionEvent event) { textField.setText(message); } }; }

16. User Interface Action (4)
Answer:
public static ActionListener createGreetingButtonListener(final String message) {
return new ActionListener() { public void actionPerformed(ActionEvent event) { textField.setText(message); } }; }

17. User Interface Action (5)
Public class ActionTest {
Public static void main(String[] args) …
textField = new JTextField(FIELD_SIZE);
helloButton.addActionListener(
creatGreetingButtonListener(“Hello, World !”));
goodbyeButton. addActionListener(
creatGreetingButtonListener(“Goodbye, World !”)); }
// the helper method in the previous slide places here

18. Timers (1) Javax.swing package
Timer generates a sequence of action events spaced apart at equal time interval, and notifies a designated action listener.
ActionListener listener = ...; final int DELAY = 1000; // 1000 millisec = 1 sec Timer t = new Timer(DELAY, listener); t.start();
 The start method returns immediately. A new thread of execution is started that issues action events in the specified frequency.

19. Timers (2)
Ch4/timer/TimerTester.java

20. Designing an Interface Type (1)
Public class ShapeIcon implements Icon {
Public void paintIcon(Component c, Graphics g, int x, int y)
Paint the shape } …

21. Designing an Interface Type (2)
ShapeIcon icon = new ShapeIcon(…); JLabel label = new JLabel(icon); ActionListener listener = new ActionListener() { public void actionPerformed(ActionEvent event) move the shape label.repaint(); } };

22. Designing an Interface Type (3)
Use timer to
Move car shapes
Draw car with CarShape
Two responsibilities:
Draw shape
Move shape
Define new interface type MoveableShape
: we can decoupled the animation from the car shape.

23. Designing an Interface Type (4) CRC Card for the MoveableShape Interface Type

24. Designing an Interface Type (5)
Name the methods to conform to standard library
public interface MoveableShape {    void draw(Graphics2D g2);    void translate(int dx, int dy); }
CarShape class implements MoveableShape public class CarShape implements MoveableShape {    public void translate(int dx, int dy)    { x += dx; y += dy; }    }

25. Designing an Interface Type (6) Implementing the Animation
Label contains icon that draws shape
Timer action moves shape, calls repaint on label
Label needs Icon, we have MoveableShape
Supply ShapeIcon adapter class
ShapeIcon.paintIcon calls MoveableShape.draw

26. Designing an Interface Type (7) Implementing the Animation

27. Designing an Interface Type (8) Implementing the Animation
Ch4/animation/MoveableShape.java
Ch4/animation/ShapeIcon.java
Ch4/animation/AnimationTester.java
Ch4/animation/CarShape.java