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

©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

©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

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 4 Chapter 10: Event Handling 4 Figure 1 Event Classes

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 5 Chapter 10: Event Handling 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)

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 6 Chapter 10: Event Handling 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 }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 7 Chapter 10: Event Handling 7 Adding the listener public class MouseSpyApplet { public MouseSpyApplet() { MouseSpy listener = new MouseSpy(); addMouseListener(listener); } }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 8 Chapter 10: Event Handling 8 Figure 2 Spying on Mouse Events

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 9 Chapter 10: Event Handling 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

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

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 11 Chapter 10: Event Handling 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() } }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 12 Chapter 10: Event Handling 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

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 13 Chapter 10: Event Handling 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(); } } }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 14 Chapter 10: Event Handling 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

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 15 Chapter 10: Event Handling 15 Figure 3 An Inner-Class Object Remembers the Outer-Class Object That Constructed It

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 16 Chapter 10: Event Handling 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); }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 17 Chapter 10: Event Handling 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 )

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 18 Chapter 10: Event Handling 18 egg.setFrame(mouseX - EGG_WIDTH / 2, mouseY - EGG_HEIGHT / 2, EGG_WIDTH, EGG_HEIGHT); repaint(); }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 19 Chapter 10: Event Handling 19 Figure 4 Handling Mouse Events

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 20 Chapter 10: Event Handling 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

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 21 Chapter 10: Event Handling 21 Figure 5 A Frame Window

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 22 Chapter 10: Event Handling 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); }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 23 Chapter 10: Event Handling 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

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 24 Chapter 10: Event Handling 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(); }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 25 Chapter 10: Event Handling 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); }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 26 Chapter 10: Event Handling 26 Add GUI components Panels (for drawing) Text fields (for text input) Buttons Menus

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 27 Chapter 10: Event Handling 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 } }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 28 Chapter 10: Event Handling 28 Figure 6 Anatomy of a Swing Frame

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 29 Chapter 10: Event Handling 29 Layout Manager Content pane uses the border layout by default Container contentPane = getContentPane(); contentPane.add(myPanel, "Center");

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 30 Chapter 10: Event Handling 30 Figure 7 Component Areas of a Border Layout

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 31 Chapter 10: Event Handling 31 Text input JTextField textField = new JTextField(); contentPane.add(textField, "South"); JTextField generates action events ActionListener interface has a single method: actionPerformed

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 32 Chapter 10: Event Handling 32 Figure 8 A Frame with a Text Field

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 33 Chapter 10: Event Handling 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(""); } }

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 34 Chapter 10: Event Handling 34 Figure 9 Drawing Random Eggs

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 35 Chapter 10: Event Handling 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;

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 36 Chapter 10: Event Handling 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();

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 37 Chapter 10: Event Handling 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

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 38 Chapter 10: Event Handling 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;

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 39 Chapter 10: Event Handling 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 count the new number of eggs */

©2000, John Wiley & Sons, Inc. Horstmann/Java Essentials, 2/e 40 Chapter 10: Event Handling 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; }