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. Grid Layout GridLayout layout = new GridLayout(3, 3); panel.setLayout(layout); button1 = new JButton( "1" ); panel.add( button1 ); button2 = new JButton( "2" ); panel.add( button2 ); button3 = new JButton( "3" ); panel.add( button3 ); button4 = new JButton( "4" ); panel.add( button4 ); ... ... ... ... ... Components are stretched to occupy the whole panel area. 3x3 GridLayout 4x1 GridLayout BorderLayout

9. Border Layout BorderLayout layout = new BorderLayout(); panel.setLayout(layout); button1 = new JButton( "North" ); panel.add( button1, BorderLayout.NORTH ); button2 = new JButton( "South" ); panel.add( button2, BorderLayout.SOUTH ); button3 = new JButton( "East" ); panel.add( button3, BorderLayout.EAST ); button4 = new JButton( "West" ); panel.add( button4, BorderLayout.WEST ); button5 = new JButton( "Center" ); panel.add( button5, BorderLayout.CENTER ); Center area gets most of the space. The other areas are given only as much as they need. Not all areas need to be occupied. 3x3 GridLayout 4x1 GridLayout BorderLayout

10. Listeners • Process events from components, containers • ActionListener (JButton, Timer, JComboBox)‏ • ChangeListener (JSlider)‏ • MouseListener, MouseMotionListener (JPanel, JFrame) • Listeners are interfaces; must implement ALLspecified 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)

11. Adapter classes • Convenience classes • server as intermediaries between the available interfaces and the user-defined (listener) classes that implement the interfaces • make it possible to implement only the methods of interest

12. Adapter classes • Convenience classes • server as intermediaries between the available interfaces and the user-defined (listener) classes that implement the interfaces • make it possible to implement only the methods of interest 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

13. Adapter classes • Convenience classes • server as intermediaries between the available interfaces and the user-defined (listener) classes that implement the interfaces • make it possible to implement only the methods of interest 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); }

14. Adapter classes • Convenience classes • server as intermediaries between the available interfaces and the user-defined (listener) classes that implement the interfaces • make it possible to implement only the methods of interest abstract class MouseAdapter implements MouseListener, MouseMotionListener { … … … … … … … … … … … … … } class LineListener extends MouseAdapter { … implement only the methods of interest … }

15. File IO

16. Text File Output • PrintWriter used for writing to file; same methods as in System.out • As if output is written to the screen with the extra steps of opening a file, closing the file, and catching exceptions try { PrintWriter output = new PrintWriter("output-file.txt"); output.println("Hello"); output.printl(42); output.println(3.1459); output.close(); } catch (Exception e) { // report error }

17. Text File Input • Scanner used for reading from file; same as in CS111 • As if input is received from the keyboard with the extra steps of opening a file, closing the file, and catching exceptions • 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 } Need to know the file format Whitespaces are ignored

18. Serialization • Mechanism for making exact copies of objects • For simple classes enough to declare implements Serializable • Application – saving / reading actual objects from a file

19. Saving with Serialization • ObjectOutputStream and method writeObject(obj) try { FileOutputStream file = new FileOutputStream("pets.ser"); ObjectOutputStream output = new ObjectOutputStream(file); output.write(petsList.size()); for (Pet pet : petsList) { output.writeObject(pet); } output.close(); } catch (Exception e) { System.out.println("Could not write to file. " + e); }

20. Reading with Serialization • ObjectInputStream and method readObject() try { FileInputStream file = new FileInputStream("pets.ser"); ObjectInputStream output = new ObjectInputStream(file); int count = input.readInt(); for (int i = 0; i < count; i++) { Pet pet = input.readObject(); } output.close(); } catch (Exception e) { System.out.println("Could not read from file. " + e); }

21. Exceptions

22. Exceptions • Mechanism for handling unexpected RUN-TIME 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

23. 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); } }

24. 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 ... // }

25. extends vs. implementsclass vs. interfacemultiple inheritance

26. 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 • }

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

28. 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?

29. 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

30. 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 • }

31. 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 • }

32. 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?

33. 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