1. ©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e Chapter 10: Event Handling 1 Event Handling

2. ©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e Chapter 10: Event Handling 2 Events Mouse move Key press Button click... originate from event source processed by event listener

3. ©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e Chapter 10: Event Handling 3 Event classes Event class (e.g. MouseEvent ). Contains information about the event (e.g. mouse location) Event listener. Knows what to do when the event occurs. Implements listener interface (e.g. MouseListener ) Event source. Keeps a list of listeners and notifies them when the event occurs

4. From Horstmann/Java Essentials, 2/e 4 Figure 1 Event Classes

5. From Horstmann/Java Essentials, 2/e 5 Listening to mouse events MouseListener interface has 5 methods – void mouseClicked(MouseEvent e) – void mouseEntered(MouseEvent e) – void mouseExited(MouseEvent e) – void mousePressed(MouseEvent e) – void mouseReleased(MouseEvent e)

6. From Horstmann/Java Essentials, 2/e 6 Spying on events class MouseSpy implements MouseListener { public void mouseClicked(MouseEvent e) { System.out.println ("Mouse clicked. x=" + e.getX() + " y=" + e.getY()); } // same for other 4 listener methods }

7. From Horstmann/Java Essentials, 2/e 7 Adding the listener public class MouseSpyApplet { public MouseSpyApplet() { MouseSpy listener = new MouseSpy(); addMouseListener(listener); } }

8. From Horstmann/Java Essentials, 2/e 8 Figure 2 Spying on Mouse Events

9. From Horstmann/Java Essentials, 2/e 9 Event Adapters Most mouse listeners only need one or two of the 5 listener methods Boring to redefine the others to do nothing MouseAdapter implements all 5 methods to do nothing. Extend MouseAdapter and just override the methods you need Other listener interfaces with > 1 method also have adapters

10. From Horstmann/Java Essentials, 2/e 10 Move egg to mouse position public class EggApplet extends Applet { public EggApplet() { egg = new Ellipse2D.Double(...); } public void paint(Graphics g) { Graphics2D g2 = (Graphics2D)g; g2.draw(egg); } private Ellipse2D.Double egg; }

11. From Horstmann/Java Essentials, 2/e 11 Add mouse listener public EggApplet() {... MouseClickListener listener = new MouseClickListener(); addListener(listener); } class MouseClickListener extends MouseAdapter { public void mouseClicked(MouseEvent e) { // set egg center to // e.getX(), e.getY() } }

12. From Horstmann/Java Essentials, 2/e 12 Make the listener an inner class Listener can't access egg instance variable Make it an inner class class EggApplet {... private class MouseClickListener extends MouseAdapter {... } } Inner class methods can access outer class instance variables

13. From Horstmann/Java Essentials, 2/e 13 Inner classes class EggApplet extends Applet {... private class MouseClickListener extends MouseAdapter { public void mouseClicked (MouseEvent e) { int mouseX = e.getX(); int mouseY = e.getY(); egg.setFrame(...); repaint(); } } }

14. From Horstmann/Java Essentials, 2/e 14 Accessing outer class features Inner class has no egg instance variable Accesses outer class variable Inner class has no repaint method Calls outer class method On which EggApplet instance? The one that constructed the inner class object—the inner class object remembers who constructed it

15. From Horstmann/Java Essentials, 2/e 15 Figure 3 An Inner-Class Object Remembers the Outer-Class Object That Constructed It

16. From Horstmann/Java Essentials, 2/e 16 Program EggApplet.java import java.applet.Applet; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.geom.Ellipse2D; public class EggApplet extends Applet { public EggApplet() { egg = new Ellipse2D.Double(0, 0, EGG_WIDTH, EGG_HEIGHT); // add mouse click listener MouseClickListener listener = new MouseClickListener(); addMouseListener(listener); }

17. From Horstmann/Java Essentials, 2/e 17 public void paint(Graphics g) { Graphics2D g2 = (Graphics2D)g; g2.draw(egg); } private Ellipse2D.Double egg; private static final double EGG_WIDTH = 30; private static final double EGG_HEIGHT = 50; // inner class definition private class MouseClickListener extends MouseAdapter { public void mouseClicked(MouseEvent event) { int mouseX = event.getX(); int mouseY = event.getY(); // now move the ellipse to ( mouseX, mouseY )

18. From Horstmann/Java Essentials, 2/e 18 egg.setFrame(mouseX - EGG_WIDTH / 2, mouseY - EGG_HEIGHT / 2, EGG_WIDTH, EGG_HEIGHT); repaint(); }

19. From Horstmann/Java Essentials, 2/e 19 Figure 4 Handling Mouse Events

20. From Horstmann/Java Essentials, 2/e 20 Graphical Applications Live inside frame window Set size and title Call show method That ends the main method, but the program keeps running GUI thread handles events

21. From Horstmann/Java Essentials, 2/e 21 Figure 5 A Frame Window

22. From Horstmann/Java Essentials, 2/e 22 Program FrameTest1.java import javax.swing.JFrame; public class FrameTest1 { public static void main(String[] args) { EmptyFrame frame = new EmptyFrame(); frame.setTitle("Frame Test"); frame.show(); } class EmptyFrame extends JFrame { public EmptyFrame() { final int DEFAULT_FRAME_WIDTH = 300; final int DEFAULT_FRAME_HEIGHT = 300; setSize(DEFAULT_FRAME_WIDTH, DEFAULT_FRAME_HEIGHT); }

23. From Horstmann/Java Essentials, 2/e 23 Quitting Graphical Apps Define window closer: class WindowCloser extends WindowAdapter { public void windowClosing (WindowEvent e) { System.exit(0); } } Add as window listener to the frame

24. From Horstmann/Java Essentials, 2/e 24 Program FrameTest2.java import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; import javax.swing.JFrame; public class FrameTest2 { public static void main(String[] args) { EmptyFrame frame = new EmptyFrame(); frame.setTitle("Close me!"); frame.show(); }

25. From Horstmann/Java Essentials, 2/e 25 class EmptyFrame extends JFrame { public EmptyFrame() { final int DEFAULT_FRAME_WIDTH = 300; final int DEFAULT_FRAME_HEIGHT = 300; setSize(DEFAULT_FRAME_WIDTH, DEFAULT_FRAME_HEIGHT); WindowCloser listener = new WindowCloser(); addWindowListener(listener); } private class WindowCloser extends WindowAdapter { public void windowClosing(WindowEvent event) { System.exit(0); }

26. From Horstmann/Java Essentials, 2/e 26 Add GUI components Panels (for drawing) Text fields (for text input) Buttons Menus

27. From Horstmann/Java Essentials, 2/e 27 Drawing on a Panel public class MyPanel extends JPanel { public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D)g; // your drawing code here } }

28. From Horstmann/Java Essentials, 2/e 28 Figure 6 Anatomy of a Swing Frame

29. From Horstmann/Java Essentials, 2/e 29 Layout Manager Content pane uses the border layout by default Container contentPane = getContentPane(); contentPane.add(myPanel, "Center");

30. From Horstmann/Java Essentials, 2/e 30 Figure 7 Component Areas of a Border Layout

31. From Horstmann/Java Essentials, 2/e 31 Text input JTextField textField = new JTextField(); contentPane.add(textField, "South"); JTextField generates action events ActionListener interface has a single method: actionPerformed

32. From Horstmann/Java Essentials, 2/e 32 Figure 8 A Frame with a Text Field

33. From Horstmann/Java Essentials, 2/e 33 Processing Text Input class TextFieldListener implements ActionListener { public void actionPerformed (ActionEvent event) { // get user input String input = textField.getText(); // process input... // clear text field input.setText(""); } }

34. From Horstmann/Java Essentials, 2/e 34 Figure 9 Drawing Random Eggs

35. From Horstmann/Java Essentials, 2/e 35 Program Eggs.java import java.awt.Container; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; import java.awt.geom.Ellipse2D; import java.util.Random; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JTextField;

36. From Horstmann/Java Essentials, 2/e 36 public class Eggs { public static void main(String[] args) { EggFrame frame = new EggFrame(); frame.setTitle("Enter number of eggs"); frame.show(); } class EggFrame extends JFrame { public EggFrame() { final int DEFAULT_FRAME_WIDTH = 300; final int DEFAULT_FRAME_HEIGHT = 300; setSize(DEFAULT_FRAME_WIDTH, DEFAULT_FRAME_HEIGHT); addWindowListener(new WindowCloser()); // construct components panel = new EggPanel();

37. From Horstmann/Java Essentials, 2/e 37 textField = new JTextField(); textField.addActionListener(new TextFieldListener()); // add components to content pane Container contentPane = getContentPane(); contentPane.add(panel, "Center"); contentPane.add(textField, "South"); } private JTextField textField; private EggPanel panel; private class TextFieldListener implements ActionListener { public void actionPerformed(ActionEvent event) { // get user input String input = textField.getText(); // process user input

38. From Horstmann/Java Essentials, 2/e 38 panel.setEggCount(Integer.parseInt(input)); // clear text field textField.setText(""); } private class WindowCloser extends WindowAdapter { public void windowClosing(WindowEvent event) { System.exit(0); } class EggPanel extends JPanel { public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D)g;

39. From Horstmann/Java Essentials, 2/e 39 // draw eggCount ellipses with random centers Random generator = new Random(); for (int i = 0; i < eggCount; i++) { double x = getWidth() * generator.nextDouble(); double y = getHeight() * generator.nextDouble(); Ellipse2D.Double egg = new Ellipse2D.Double(x, y, EGG_WIDTH, EGG_HEIGHT); g2.draw(egg); } /** Sets the number of eggs to be drawn and repaints the panel. @param count the new number of eggs */

40. From Horstmann/Java Essentials, 2/e 40 public void setEggCount(int count) { eggCount = count; repaint(); } private int eggCount; private static final double EGG_WIDTH = 30; private static final double EGG_HEIGHT = 50; }