GUI

1. GUI

2. Swing Class Hierarchy

3. Swing Components

4. Swing Conatiners • JFrame – top-level window to store components

5. Swing Conatiners • JPanel – container; can be embedded in JFrame

6. Layouts • FlowLayout • arranges elements in a row • elements centered by default within container • GridLayout • subdivides container into cells of identical sizes • components take up all available space of a cell • BorderLayout • subdivides container into 5 areas: N, S, E, W, Center

7. Layouts 3x3 GridLayout 4x1 GridLayout BorderLayout FlowLayout used to place the 3 panels in the Jframe.

8. Listeners • Process events • ActionListener (JButton, Timer, JComboBox)‏ • ChangeListener (JSlider)‏ • MouseListener, MouseMotionListener • Listeners are interfaces; must implement ALL specified methods • ActionListener: void actionPerformed(ActionEvent e)‏ • ChangeListener: void stateChanged(ChangeEvent e)‏ • MouseListener: void mouseClicked(MouseEvent e) void mousePressed(MouseEvent e) void mouseReleased(MouseEvent e) void mouseEntered(MouseEvent e) void mouseExited(MouseEvent e)‏ • MouseMotionListener: void mouseMoved(MouseEvent e)void mouseDragged(MouseEvent e)

9. Adapter classes • Convenience classes • server as intermediaries between available interfaces (e.g. listeners) and the user defined classes (e.g. listeners) • make it possible to implement only the “important” methods

10. Adapter classes • Convenience classes • server as intermediaries between available interfaces (e.g. listeners) and the user defined classes (e.g. listeners) • make it possible to implement only the “important” methods abstract class MouseAdapter implements MouseListener, MouseMotionListener { void mousePressed(MouseEvent e) { // empty body } void mouseReleased(MouseEvent e) { // empty body } void mouseEntered(MouseEvent e) { // empty body } void mouseExited(MouseEvent e) { // empty body } void mouseMoved(MouseEvent e) { // empty body } void mouseDragged(MouseEvent e) { // empty body } } MouseListener methods MouseMotionListener methods

11. Adapter classes • Convenience classes • server as intermediaries between available interfaces (e.g. listeners) and the user defined classes (e.g. listeners) • make it possible to implement only the “important” methods abstract class MouseAdapter implements MouseListener, MouseMotionListener { abstract void mousePressed(MouseEvent e); abstract void mouseReleased(MouseEvent e); abstract void mouseEntered(MouseEvent e); abstract void mouseExited(MouseEvent e); abstract void mouseMoved(MouseEvent e); asbtract void mouseDragged(MouseEvent e); }

12. File IO

13. File IO • PrintWriter – for writing to file; same methods as in System.out • Pretend that all output goes to screen try { PrintWriter output = new PrintWriter(“input-file.txt”); output.println(“Hello”); output.printl(42); output.println(“3.1459”); output.close(); } catch (Exception e) { // report error }

14. File IO • Scanner – for reading from file; same as in CS111 • Contents is viewed as a stream of characters • Reading stops as soon as appropriate token found; otherwise fails try { Scanner input = new Scanner(new File(“input-file.txt”)); String word = input.next(); int answer = input.nextInt(); double pi = input.nextDouble(); input.close(); } catch (Exception e) { // report error }

15. Command-Line

16. Command Line Arguments • Make it possible to send data to the program on execution public static void main(String[] args)‏ { System.out.println(“Parameters given on start-up:”); System.out.println(“Number of params: “ + args.length); for (int i = 0; i < args.length; i++) { System.out.println(args[i]); // i-th parameter value } }

17. Exceptions

18. Exceptions • Mechanism for handling unexpected conditions (errors)‏ • Force the programmer to handle error conditions • Allow for separating the logic of the code from error-handling • Sometimes no other option to report the value: • constructor • minElement, maxElement • Example – see FileIO

19. Exceptions • Can create our own type of exception (should inherit from Exception)‏ class EmptyArrayException extends Exception { public void EmptyArrayException()‏ { super(); } public void EmptyArrayException(String message)‏ { super(message); } }

20. Exceptions • Example of our own Exception --- throw/throws int minElement(int[] numbers) throws EmptyArrayException { // empty array --- throw an exception if (numbers.length == 0)‏ { throw EmptyArrayException(“Empty array given”); } // // ... compute smallest element ... // }

21. extends vs. implementsclass vs. interfacemultiple inheritance

22. Interfaces • An interface specifies a collection of methods • An interface does not have data members or code for methods • A class that implements the interface must provide code (implementation) for all methods listed in the interface • interface RemoteControllable • { • public void play(); • public void stop(); • public void ffwd(); • } • class VCR implements RemoteControllable • { • // must provide code for all methods in RemoteControllable • } • class DVD implements RemoteControllable • { • // must provide code for all methods in RemoteControllable • }

23. Multiple Inheritance Class Mammal Class Pet String name; //species void setName(String n) { ... ... ... } String name; // pet’s name void setName(String n) { ... ... ... } Class Cat

24. Multiple Inheritance Class Mammal Class Pet String name; //species void setName(String n) { ... ... ... } String name; // pet’s name void setName(String n) { ... ... ... } Class Cat Which name is inherited? Which setName() is inherited?

25. Multiple Inheritance Class Mammal Class Pet String name; //species void setName(String n) { ... ... ... } String name; // pet’s name void setName(String n) { ... ... ... } Class Cat Which name is inherited? Which setName() is inherited? • Complex rules required to disambiguate in multiple inheritance • Java does not support multiple inheritance; C++ does

26. Multiple Inheritance • What if we still want a Cat to behave like a Mammal and Pet • interface Mammal • { • // all methods (behaviors) common to mammals • // no code is specified, just the behavior names (methods) • } • class Pet • { • // description of generic pet • } • class Cat extends Pet implements Mammal • { • // has all behaviors of a Pet – could override some • // must implement all behaviors of Mammal • }

27. Multiple Inheritance • Can now use Cat objects anywhere Mammal behaviors required or where Pet objects are required • public void hunt(Mammal predator, Mammal prey) • { • // do something; could send a Cat as • // either prey or predator • } • public void doTricks(Pet pet) • { • // do something; could send a Cat for pet • }

28. Multiple Interfaces Implementation • A Java class can only extend from one other class (single inheritance) • A Java class can implement multiple interfaces – can ambiguity arise?

29. Multiple Interfaces Implementation • A Java class can only extend from one other class (single inheritance) • A Java class can implement multiple interfaces – no ambiguity since • an interface cannot have data members • an interface cannot have code (implementation) for methods