chapter 10 event handling. chapter goals to understand the java event model to install mouse and...

CHAPTER 10

EVENT HANDLING

CHAPTER GOALS

• To understand the Java event model

• To install mouse and action listeners

• To accept mouse and text input

• To display frame windows  

• To show text output in a text area with a

scroll bar

Event Classes• Event source: Generates events and manages

listenersExample: applet

• Listener: Notified when event happensExample: MouseListener

• Event class: Describes eventExample: MouseEvent

The MouseListener Interface public interface MouseListener

{ void mousePressed(MouseEvent event); //Called when a mouse button has been pressed on a componentvoid mouseReleased(MouseEvent event);  //Called when a mouse button has been released on a componentvoid mouseClicked(MouseEvent event); //Called when the mouse has been clicked on a componentvoid mouseEntered(MouseEvent event); //Called when the mouse enters a component void mouseExited(MouseEvent event); //Called when the mouse exits a component

}

File MouseSpy.java1 import java.awt.event.MouseEvent;

2 import java.awt.event.MouseListener;

3

4 /**

5 This listener simply prints out the listener method name

6 and the x- and y-coordinate of the mouse position.

7 */

8 public class MouseSpy implements MouseListener

9 {

10 public void mousePressed(MouseEvent event)

11 {

12 System.out.println("Mouse pressed. x = "

13 + event.getX() + " y = " + event.getY());

14 }

15

16 public void mouseReleased(MouseEvent event)

17 {

18 System.out.println("Mouse released. x = "

19 + event.getX() + " y = " + event.getY());

20 }

21

22 public void mouseClicked(MouseEvent event)

23 {

24 System.out.println("Mouse clicked. x = "

25 + event.getX() + " y = " + event.getY());

26 }

27

28 public void mouseEntered(MouseEvent event)

29 {

30 System.out.println("Mouse entered. x = "

31 + event.getX() + " y = " + event.getY());

32 }

33

34 public void mouseExited(MouseEvent event)

35 {

36 System.out.println("Mouse exited. x = "

37 + event.getX() + " y = " + event.getY());

38 }

39 }

File MouseSpyApplet.java1 import java.applet.Applet;

2

3 /**

4 This applet installs a mouse spy. Try generating the

5 five mouse event types by moving and clicking the mouse.

6 */

7 public class MouseSpyApplet extends Applet

8 {

9 public MouseSpyApplet()

10 {

11 MouseSpy listener = new MouseSpy();

12 addMouseListener(listener);

13 }

14 }

15

Spying on Mouse Events

Mouse Listener that Moves a Rectangle

public MouseApplet()

{ ... //add mouse press listener class MousePressListener implements MouseListener { public void mousePressed(MouseEvent event) {

int x = event.getX(); int y = event.getY(); box.setLocation(x,y); repaint();

}

//do-nothing methods public void mouseReleased(MouseEvent event){}

public void mouseClicked(MouseEvent event){}

public void mouseEntered(MouseEvent event){}

public void mouseExited(MouseEvent event){} } MouseListener listener = new MousePressListener(); addMouseListener(listener);

}

Mouse Listener that Moves a Rectangle

• Gets mouse position from event object • Accesses box instance field of outer class • Invokes repaint method on outer class • repaint triggers paint method • You should always call repaint to trigger painting

Don't call paint directly

The Mouse Applet

The Mouse Applet

An Applet with a Control Panel

Control Panel Components

• Use Swing package javax.swing • Class names start with J

• JTextField xField = new JTextField(width); • JLabel xLabel = new JLabel("x = "); • Icon buttonIcon = new ImageIcon("hand.gif");• moveButton = new JButton("Move",buttonIcon);

Button Listener• Moves rectangle when button is clicked • Reads xField, yField variables from enclosing scope public ButtonApplet() { ... class MoveButtonListener implements ActionListener { public void actionPerformed(ActionEvent event) { int x =Integer.parseInt(xField.getText()); int y =Integer.parseInt(yField.getText()); box.setLocation(x,y); repaint(); } }; ActionListener listener = new MoveButtonListener(); moveButton.addActionListener(listener); ... }

Placing Components in a Panel •JPanel is container for components • Add components to panelJPanel panel = new JPanel();panel.add(xLabel);panel.add(xField);. . .

• Place panel inside frameJFrame frame = new JFrame();frame.setContentPane(panel);

• Pack frame: size it to just contain the componentsframe.pack();frame.show();

File ButtonApplet.java 1 import java.applet.Applet;

2 import java.awt.Graphics;

3 import java.awt.Graphics2D;

4 import java.awt.Rectangle;

5 import java.awt.event.ActionEvent;

6 import java.awt.event.ActionListener;

7 import javax.swing.ImageIcon;

8 import javax.swing.JButton;

9 import javax.swing.JFrame;

10 import javax.swing.JLabel;

11 import javax.swing.JPanel;

12 import javax.swing.JTextField;

13

14 /**

15 This applet lets the user move a rectangle by specifying

16 the x- and y-position of the top left corner.

17 */

18 public class ButtonApplet extends Applet

19 {

20 public ButtonApplet()

21 {

22 // the rectangle that the paint method draws

23 box = new Rectangle(BOX_X, BOX_Y,

24 BOX_WIDTH, BOX_HEIGHT);

25

26 // the text fields for entering the x- and y-coordinates

27 final JTextField xField = new JTextField(5);

28 final JTextField yField = new JTextField(5);;

29

30 // the button to move the rectangle

31 JButton moveButton = new JButton("Move",

32 new ImageIcon("hand.gif"));

33

34 class MoveButtonListener implements ActionListener

35 {

36 public void actionPerformed(ActionEvent event)

37 {

38 int x = Integer.parseInt(xField.getText());

39 int y = Integer.parseInt(yField.getText());

40 box.setLocation(x, y);

41 repaint();

42 }

43 };

44

45 ActionListener listener = new MoveButtonListener();

46 moveButton.addActionListener(listener);

47

48 // the labels for labeling the text fields

49 JLabel xLabel = new JLabel("x = ");

50 JLabel yLabel = new JLabel("y = ");

51

52 // the panel for holding the user interface components

53 JPanel panel = new JPanel();

54

55 panel.add(xLabel);

56 panel.add(xField);

57 panel.add(yLabel);

58 panel.add(yField);

59 panel.add(moveButton);

60

61 // the frame for holding the component panel

62 JFrame frame = new JFrame();

63 frame.setContentPane(panel);

64 frame.pack();

65 frame.show();

66 }

67

68 public void paint(Graphics g)

69 {

70 Graphics2D g2 = (Graphics2D)g;

71 g2.draw(box);

72 }

73

74 private Rectangle box;

75 private static final int BOX_X = 100;

76 private static final int BOX_Y = 100;

77 private static final int BOX_WIDTH = 20;

78 private static final int BOX_HEIGHT = 30;

79 }

Multiple Buttons with Similar Behavior

• Don't want to write separate code for similar listeners

• Remedy: Write method that attaches the listener

• Make variable parts into final method parameters • Local listener class can access final parameters

An Applet with Multiple Buttons

Method for Attaching Listenerpublic JButton makeButton(String label, final int dx,final int dy) { JButton button = new JButton(label); class ButtonListener implements ActionListener { public void actionPerformed(ActionEvent event) { box.translate(dx, dy); repaint(); } };

ButtonListener listener = new ButtonListener(); button.addActionListener(listener); return button; }

Method for Attaching Listener

• Call multiple times

panel.add(makeButton("Left",-BOX_WIDTH,0)); panel.add(makeButton("Right",BOX_WIDTH,0)); panel.add(makeButton("Up",0,-BOX_HEIGHT)); panel.add(makeButton("Down",0,BOX_HEIGHT));

File ButtonApplet.java 1 import java.applet.Applet;

2 import java.awt.Graphics;

3 import java.awt.Graphics2D;

4 import java.awt.Rectangle;

5 import java.awt.event.ActionEvent;

6 import java.awt.event.ActionListener;

7 import javax.swing.JButton;

8 import javax.swing.JFrame;

9 import javax.swing.JPanel;

10

11 /**

12 This applet lets the user move a rectangle by clicking

13 on buttons labeled "Left", "Right", "Up", and "Down".

14 */

15 public class ButtonApplet extends Applet

16 {

17 public ButtonApplet()

18 {

19 // the rectangle that the paint method draws

20 box = new Rectangle(BOX_X, BOX_Y,

21 BOX_WIDTH, BOX_HEIGHT);

22

23 // the panel for holding the user interface components

24 JPanel panel = new JPanel();

25

26 panel.add(makeButton("Left", -BOX_WIDTH, 0));

27 panel.add(makeButton("Right", BOX_WIDTH, 0));

28 panel.add(makeButton("Up", 0, -BOX_HEIGHT));

29 panel.add(makeButton("Down", 0, BOX_HEIGHT));

30

31 // the frame for holding the component panel

32 JFrame frame = new JFrame();

33 frame.setContentPane(panel);

34 frame.pack();

35 frame.show();

36 }

37

38 public void paint(Graphics g)

39 {

40 Graphics2D g2 = (Graphics2D)g;

41 g2.draw(box);

42 }

43

44 /**

45 Makes a button that moves the box.

46 @param label the label to show on the button

47 @param dx the amount by which to move the box in x-direction

48 when the button is clicked

49 @param dy the amount by which to move the box in y-direction

50 when the button is clicked

51 @return the button

52 */

53 public JButton makeButton(String label, final int dx,

54 final int dy)

55 {

56 JButton button = new JButton(label);

57

58 class ButtonListener implements ActionListener

59 {

60 public void actionPerformed(ActionEvent event)

61 {

62 box.translate(dx, dy);

63 repaint();

64 }

65 };

66

67 ButtonListener listener = new ButtonListener();

68 button.addActionListener(listener);

69 return button;

70 }

71

72 private Rectangle box;

73 private static final int BOX_X = 100;

74 private static final int BOX_Y = 100;

75 private static final int BOX_WIDTH = 20;

76 private static final int BOX_HEIGHT = 30;

77 }

Frame Windows• Application program, not applet

• Construct and show frameJFrame frame = new JFrame();. . .frame.show();

• Set the default close operationframe.setDefaultCloseOperation(EXIT_ON_CLOSE);

• Add components to a panel, then set the panel as content paneJPanel panel = new JPanel();panel.add(. . .);panel.add(. . .)frame.setContentPane(panel);

A Frame with Two Labels

File FrameTest.java1 import javax.swing.ImageIcon;

2 import javax.swing.JFrame;

3 import javax.swing.JLabel;

4 import javax.swing.JPanel;

5

6 /**

7 This program displays a frame with an image and a text label.

8 */

9 public class FrameTest

10 {

11 public static void main(String[] args)

12 {

13 JFrame frame = new JFrame();

14 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

15

16 JLabel iconLabel = new JLabel(new ImageIcon("world.gif"));

17 JLabel textLabel = new JLabel("Hello, World!");

18

19 JPanel panel = new JPanel();

20 panel.add(iconLabel);

21 panel.add(textLabel);

22 frame.setContentPane(panel);

23

24 frame.pack();

25 frame.show();

26 }

27 }

Text Components • JTextField holds a single line of text • JTextArea holds multiple lines

• Construct with new JTextArea(rows, columns)

• textArea.append(aString) appends text

• Use textArea.setEditable(false) to use for display only

• To add scroll bars, useJScrollPane scrollPane = new JScrollPane(textArea);

textArea.setContentPane(scrollPane);

A Text Area with Scroll Bars

The Control Panel for Adding Interest

File TextAreaTest.java1 import java.awt.event.ActionEvent;

2 import java.awt.event.ActionListener;

3 import javax.swing.JButton;

4 import javax.swing.JFrame;

5 import javax.swing.JLabel;

6 import javax.swing.JPanel;

7 import javax.swing.JScrollPane;

8 import javax.swing.JTextArea;

9 import javax.swing.JTextField;

10

11 /**

12 This program shows a frame with a text area that displays

13 the growth of an investment. A second frame holds a text

14 field to specify the interest rate.

15 */

16 public class TextAreaTest

17 {

18 public static void main(String[] args)

19 {

20 // the application adds interest to this bank account

21 final BankAccount account = new BankAccount(INITIAL_BALANCE);

22 // the text area for displaying the results

23 final JTextArea textArea = new JTextArea(10, 30);

24 textArea.setEditable(false);

25 JScrollPane scrollPane = new JScrollPane(textArea);

26

27 // construct the frame for displaying the text area

28 JFrame frame = new JFrame();

29 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

30 frame.setContentPane(scrollPane);

31 frame.pack();

32 frame.show();

33

34 // the label and text field for entering the interest rate

35 JLabel rateLabel = new JLabel("Interest Rate: ");

36

37 final JTextField rateField = new JTextField(10);

38 rateField.setText("" + DEFAULT_RATE);

39

40 // the button to trigger the calculation

41 JButton calculateButton = new JButton("Add Interest");

42

43 class CalculateListener implements ActionListener

44 {

45 public void actionPerformed(ActionEvent event)

46 {

47 double rate = Double.parseDouble(

48 rateField.getText());

49 double interest = account.getBalance()

50 * rate / 100;

51 account.deposit(interest);

52 textArea.append(account.getBalance() + "\n");

53 }

54 }

55

56 ActionListener listener = new CalculateListener();

57 calculateButton.addActionListener(listener);

58

59 // the control panel that holds the input components

60 JPanel controlPanel = new JPanel();

61 controlPanel.add(rateLabel);

62 controlPanel.add(rateField);

63 controlPanel.add(calculateButton);

64

65 // the frame to hold the control panel

66 JFrame controlFrame = new JFrame();

67 controlFrame.setContentPane(controlPanel);

68 controlFrame.pack();

69 controlFrame.show();

70 }

71

72 private static final double DEFAULT_RATE = 10;

73 private static final double INITIAL_BALANCE = 1000;

74 }