Bài giảng Công nghệ Java - Chương 10: Handling Mouse and Keyboard Events - SWING components - Lê Nhật Tùng

CÔNG NGHỆ JAVA
CH10. Handling Mouse and
Keyboard Events - SWING components
Giảng viên: Lê Nhật Tùng
www.lenhattung.com
4/7/2018  1
 2
Topics in This Section
Basic of Event Handling
General asynchronous event-handling strategy
Event-handling options
Handling events with separate listeners
Handling events by implementing interfaces
Handling events with named inner classes
Handling events with anonymous inner classes
The standard AWT listener types
Subtleties with mouse events
Examples
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Basic of Event Handling
Every time the user types a character or pushes a mouse button, an event 
occurs. 
•Events: Objects that describe what happened
•Event sources: The generator of an event
•Event handlers: A method that receives an event object, deciphers it, and 
processes the user’s interaction.
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Delegation Model of Event
An event can be sent to many event handlers.
Event handlers register with components when 
they are interested in events generated by that 
component.
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A Listener Example
public class TestButton {
JFrame frame;
JButton button;
public TestButton() {
frame = new JFrame("Test");
button = new JButton("Press Me!");
button.setActionCommand("ButtonPressed");
// register event listener for button
button.addActionListener(new ButtonHandler());
frame.add(button, BorderLayout.CENTER);
}
public void launchFrame() {
frame.pack();
frame.setVisible(true);
}
}
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A Listener Example (Contd.)
class ButtonHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("Action occurred");
System.out.println("Button’s command is: " +
e.getActionCommand());
}
}
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Event Categories
Class Hierarchy of GUI Events:
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Listener Type
Some Events and Their Associated Event 
Listeners:
Act that Results in the Event Listener Type
User clicks a button, presses Enter while 
typing in a text field, or chooses a menu 
item 
ActionListener 
User closes a frame (main window) WindowListener 
User presses a mouse button while the 
cursor is over a component 
MouseListener 
User moves the mouse over a component MouseMotionListener 
Component becomes visible ComponentListener 
Component gets the keyboard focus FocusListener 
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Listeners
•ActionListener Interface:
–Has only one method: actionPerformed(ActionEvent)
–To detect when the user clicks an onscreen button (or does 
the keyboard equivalent), a program must have an object 
that implements the ActionListener interface.
–The program must register this object as an action listener 
on the button (the event source), using the 
addActionListener() method.
–When the user clicks the onscreen button, the button fires 
an action event.
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Listeners (Contd.)
MouseListener interface:
To detect the mouse clicking, a program must 
have an object that implements the 
MouseListener interface.
This interface includes several events including 
mouseEntered, mouseExited, mousePressed, 
mouseReleased, and mouseClicked.
When the user clicks the onscreen button, the 
button fires an action event.
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Listeners (Contd.)
Implementing Multiple Interfaces:
A class can be declared with Multiple Interfaces 
by using comma separation:
implements MouseListener, MouseMotionListener
Listening to Multiple Sources:
Multiple listeners cause unrelated parts of a 
program to react to the same event.
The handlers of all registered listeners are 
called when the event occurs.
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General Strategy
Determine what type of listener is of interest
11 standard AWT listener types.
ActionListener, ItemListener, KeyListener, 
MouseListener, MouseMotionListener, TextListener, 
AdjustmentListener, ComponentListener, 
ContainerListener, FocusListener, WindowListener
Define a class of that type
Implement interface (KeyListener, MouseListener, )
Extend class (KeyAdapter, MouseAdapter, etc.)
Register an object of your listener class with the 
component
comp.addXxxListener(new MyListenerClass());
E.g., addKeyListener, addMouseListener
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Case 1 - Using Separate 
Listener Classes
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Separate Listener: Simple Case
Listener does not need to call any methods 
of the window to which it is attached
public class MouseClickFrame extends JFrame {
public MouseClickFrame(String title) {
super(title);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addMouseListener(new ClickListener());
setSize(300, 400);
setVisible(true);
}
public static void main(String[] args) {
new MouseClickFrame("Mouse Click");
}
}
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Separate Listener: Simple Case
class ClickListener extends MouseAdapter {
private int radius = 25;
public void mousePressed(MouseEvent event) {
JFrame comp = (JFrame) event.getSource();
Graphics g = comp.getGraphics();
g.fillOval(event.getX() - radius, 
event.getY() - radius, 
2 * radius, 2 * radius);
}
}
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Separate Listener: Simple Case (Cont')
•Register an object of ClickListener for frame
•Define a class ClickListener extends 
MouseAdapter class and override mousePress() 
method.
•General event Handling :
–Call event.getSource() to obtain a reference to 
window or GUI component from which event originated
–Cast result to type of interest
–Call methods on that reference
•get a Graphics object of component (frame) and draw
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MouseListener and MouseAdapter
public interface MouseListener {
public void mouseClicked(MouseEvent e);
public void mousePressed(MouseEvent e);
public void mouseReleased(MouseEvent e);
public void mouseEntered(MouseEvent e);
public void mouseExited(MouseEvent e);
}
public abstract class MouseAdapter implements MouseListener 
{
public void mouseClicked(MouseEvent e) {}
public void mousePressed(MouseEvent e) {}
public void mouseReleased(MouseEvent e) {}
public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
}
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Implementing a Listener Interface
class ClickListener implements MouseListener {
private int radius = 25;
public void mousePressed(MouseEvent event) {
JFrame app = (JFrame) event.getSource();
Graphics g = app.getGraphics();
g.fillOval(event.getX() - radius, 
event.getY() - radius, 
2 * radius, 2 * radius);
}
public void mouseClicked(MouseEvent e) { }
public void mouseReleased(MouseEvent e) { }
public void mouseEntered(MouseEvent e) { }
public void mouseExited(MouseEvent e) {}
}
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Implementing a Listener Interface
public class MouseClickFrame extends JFrame {
public MouseClickFrame(String title) {
super(title);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addMouseListener(new ClickListener());
setSize(300, 400);
setVisible(true);
}
public static void main(String[] args) {
new MouseClickFrame("Mouse Click");
}
}
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Adapters vs. Interfaces: Method Signature Errors
•What if you goof on the method signature?
–public void mousepressed(MouseEvent e)
–public void mousePressed()
•Interfaces
–Compile time error
•Adapters
–No compile time error, but nothing happens at run time 
when you press the mouse
•Solution for adapters: @Override annotation
–Whenever you think you are overriding a method, put 
@Override on the line above the start of the method.
–If that method is not actually overriding an inherited 
method, you get a compile-time error.
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@Override Example
class ClickListener extends MouseAdapter {
private int radius = 25;
@Override
public void mousePressed(MouseEvent event) {
JFrame comp = (JFrame) event.getSource();
Graphics g = comp.getGraphics();
g.fillOval(event.getX() - radius, 
event.getY() - radius, 
2 * radius, 2 * radius);
}
}
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Case 2 – Main window 
implements interface
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Main window implements interface
public class MouseClickFrame extends JFrame 
implements MouseListener {
private int radius = 25;
public MouseClickFrame(String title) {
super(title);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addMouseListener(this);
setSize(300, 400);
setVisible(true);
}
public void mousePressed(MouseEvent event) {
Graphics g = this.getGraphics();
g.fillOval(event.getX() - radius, event.getY() - radius, 
2 * radius, 2 * radius);
}
public void mouseClicked(MouseEvent e) { }
public void mouseReleased(MouseEvent e) { }
public void mouseEntered(MouseEvent e) { }
public void mouseExited(MouseEvent e) { }
}
Refer to current 
MouseClickFrame object
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Using Inner Classes
(Named & Anonymous)
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Review of Inner Classes
Class can be defined inside another class
Methods in the inner class can access all methods and 
instance variables of surrounding class
Even private methods and variables
Example
public class OuterClass {
private int count = ...;
public void foo(...) {
InnerClass inner = new
InnerClass();
inner.bar();
}
private class InnerClass {
public void bar() {
doSomethingWith(count);
}
}
}4/7/2018
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Case 3: Named Inner Classes
public class MouseClickFrame extends JFrame {
public MouseClickFrame(String title) {
super(title);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addMouseListener(new ClickListener())
setSize(300, 400);
setVisible(true);
}
private class ClickListener extends MouseAdapter {
private int radius = 25;
public void mousePressed(MouseEvent event) {
Graphics g = getGraphics();
g.fillOval(event.getX()-radius, event.getY()-radius, 
2 * radius, 2 * radius);
} 
}
}
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public class MouseClickFrame extends JFrame {
public MouseClickFrame(String title) {
super(title);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addMouseListener(new MouseAdapter() {
private int radius = 25;
public void mousePressed(MouseEvent event) {
Graphics g = getGraphics();
g.fillOval(event.getX()-radius, event.getY()-radius, 
2 * radius, 2 * radius);
} 
});
setSize(300, 400);
setVisible(true);
}
}
Case 4: Anonymous Inner Classes
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Anonymous Inner Classes (other)
public class MouseClickFrame extends JFrame {
public MouseClickFrame(String title) {
super(title);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
MouseListener listener = new MouseAdapter() {
private int radius = 25;
public void mousePressed(MouseEvent event) {
Graphics g = getGraphics();
g.fillOval(event.getX()-radius, event.getY()-radius, 
2 * radius, 2 * radius);
} 
};
addMouseListener(listener);
setSize(300, 400);
setVisible(true);
}
}
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Summary of
Approaches
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Event Handling Strategies: Pros and Cons
Separate Listener
Advantages
Can extend adapter and thus ignore unused methods
Separate class easier to manage
Disadvantage
Need extra step to call methods in main window
Main window that implements interface
Advantage
No extra steps needed to call methods in main window
Disadvantage
Must implement methods you might not care about
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Event Handling Strategies: Pros and Cons
•Named inner class
–Advantages
•Can extend adapter and thus ignore unused methods
•No extra steps needed to call methods in main window
–Disadvantage
•A bit harder to understand
•Anonymous inner class
–Advantages
•Same as named inner classes
•Even shorter
–Disadvantage
•Much harder to understand
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Event Handler Details
and Examples
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Standard AWT Event Listeners
Listener Adapter Class (If Any) Registration Method
ActionListener addActionListener
AdjustmentListener addAdjustmentListener
ComponentListener ComponentAdapter addComponentListener
ContainerListener ContainerAdapter addContainerListener
FocusListener FocusAdapter addFocusListener
ItemListener addItemListener
KeyListener KeyAdapter addKeyListener
MouseListener MouseAdapter addMouseListener
MouseMotionListener MouseMotionAdapter addMouseMotionListener
TextListener addTextListener
WindowListener WindowAdapter addWindowListener
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Standard AWT Event Listeners (Details)
ActionListener
Handles buttons and a few other actions
actionPerformed(ActionEvent event)
AdjustmentListener
Applies to scrolling
adjustmentValueChanged(AdjustmentEvent event)
ComponentListener
Handles moving/resizing/hiding GUI objects
componentResized(ComponentEvent event)
componentMoved(ComponentEvent event)
componentShown(ComponentEvent event)
componentHidden(ComponentEvent event)
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Standard Event Listeners (Details cont')
ContainerListener
Triggered when window adds/removes GUI 
controls
componentAdded(ContainerEvent event)
componentRemoved(ContainerEvent event)
FocusListener
Detects when controls get/lose keyboard focus
focusGained(FocusEvent event)
focusLost(FocusEvent event)
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Standard Event Listeners (Details cont')
ItemListener
Handles selections in lists, checkboxes, etc.
itemStateChanged(ItemEvent event)
KeyListener
Detects keyboard events
keyPressed(KeyEvent event) 
any key pressed down
keyReleased(KeyEvent event)
any key released
keyTyped(KeyEvent event)
key for printable char released
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Standard Event Listeners (Details cont')
MouseListener
Applies to basic mouse events
mouseEntered(MouseEvent event)
mouseExited(MouseEvent event)
mousePressed(MouseEvent event)
mouseReleased(MouseEvent event)
mouseClicked(MouseEvent event)
Release without drag. Do not use this for mousePressed!
Applies on release if no movement since press
MouseMotionListener
Handles mouse movement
mouseMoved(MouseEvent event)
mouseDragged(MouseEvent event)
MouseInputListener
Combines MouseListener and MouseMotionListener
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Standard Event Listeners (Details cont')
TextListener
Applies to textfields and text areas
textValueChanged(TextEvent event)
WindowListener
Handles high-level window events
windowOpened, windowClosing, windowClosed, 
windowIconified, windowDeiconified, 
windowActivated, windowDeactivated
windowClosing particularly useful
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Example: Simple Whiteboard
public class SimpleWhiteboard extends JApplet {
protected int lastX=0, lastY=0;
public void init() {
getContentPane().setBackground(Color.WHITE);
getContentPane().setForeground(Color.BLUE);
addMouseListener(new PositionRecorder());
addMouseMotionListener(new LineDrawer());
}
protected void record(int x, int y) {
lastX = x;
lastY = y;
}
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Simple Whiteboard (Continued)
private class PositionRecorder extends MouseAdapter {
public void mouseEntered(MouseEvent event) {
requestFocus(); // Plan ahead for typing
record(event.getX(), event.getY());
}
public void mousePressed(MouseEvent event) {
record(event.getX(), event.getY());
}
}
private class LineDrawer extends MouseMotionAdapter {
public void mouseDragged(MouseEvent event) {
int x = event.getX();
int y = event.getY();
Graphics g = getGraphics();
g.drawLine(lastX, lastY, x, y);
record(x, y);
}
}
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Simple Whiteboard (Results)
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Whiteboard: Adding Keyboard Events
public class Whiteboard extends SimpleWhiteboard {
protected FontMetrics fm;
public void init() {
super.init();
Font font = new Font("Serif", Font.BO ... ut");
frame.pack(); 
frame.setVisible(true);
}
}
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JTextField Example
Output
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JTextArea
JTextArea component is used to accept several 
lines of text from the user.
It implements the scrollable interface to activate 
scrollbars.
JTextArea component can be created using any 
one of the following constructors:
JTextArea()
JTextArea(int rows, cols)
JTextArea(String text)
JTextArea(String text, int rows, int cols)
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public class TextAreaApp extends JFrame {
public TextAreaAppln(String title) {
super(title);
setLayout(new FlowLayout());
JLabel lbl = new JLabel("Sample TextArea");
add(lbl);
JTextArea txt = new JTextArea(5, 15);
txt.setFont(new Font("Serif", Font.ITALIC, 16));
txt.setLineWrap(true);
// create croll panel contain text area
JScrollPane areaScrollPane = new JScrollPane(txt);
add(areaScrollPane);
pack();
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
JTextArea Example
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JTextArea Example
Output
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JPasswordField
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class PasswordDemo extends Jframe 
implements ActionListener {
JPasswordField txtPassword;
public PasswordDemo() { 
txtPassword = new JPasswordField(12);
txtPassword.setEchoChar('*');
JLabel lblPassword = new JLabel("Password : ");
lblPassword.setLabelFor(txtPassword);
JPanel pnlLeft = new JPanel();
// Add the Label and TextBox to the Panel
pnlLeft.add(lblPassword);
pnlLeft.add(txtPassword); 
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JPasswordField
JPanel pnlRight = new JPanel(new GridLayout(0,1));
JButton btnOk = new JButton("OK");
JButton btnCancel = new JButton("Cancel");
// Set the command string that will be used for
// handling events on the ok button
btnOk.setActionCommand("Ok");
btnCancel.setActionCommand("Cancel");
btnOk.addActionListener(this);
btnCancel.addActionListener(this);
pnlRight.add(btnOk);
pnlRight.add(btnCancel);
getContentPane().add(pnlLeft, BorderLayout.WEST);
getContentPane().add(pnlRight, BorderLayout.CENTER);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setTitle("Password Field Demo");
}
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public void actionPerformed(ActionEvent e) {
String str = e.getActionCommand();
if ("Ok".equals(str)) {
char chPassword[] = txtPassword.getPassword();
String strPassword = new String(chPassword);
if (strPassword.trim().equals("pass")) {
JOptionPane.showMessageDialog(this, "Correct Password");
} else {
JOptionPane.showMessageDialog(this, 
"Incorrect Password", "Error Message", 
JOptionPane.ERROR_MESSAGE);
}
txtPassword.selectAll();
txtPassword.requestFocusInWindow();
} else {
System.exit(0);
}
}
JPasswordField (contd)
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JPasswordField Contd
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
PasswordDemo frame = new PasswordDemo();
frame.pack();
frame.setVisible(true);
}
});
}
}
Output
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JButton
Buttons trap user action.
JButton class descends from 
javax.swing.AbstractButton class.
JButton object consists of a text label and/or image 
icon, empty area around the text/icon and border.
A JButton can be created using:
JButton()
JButton(Icon icon)
JButton(String text)
JButton(String text, Icon icon)
JButton(Action a)
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JButton Example
public class ButtonDemo extends JPanel {
JButton btnImage1, btnImage2;
String message = " ";
public ButtonDemo() {
// Create icons that display on the buttons
ImageIcon btnIcon1 = new ImageIcon("images/red-ball.gif");
ImageIcon btnIcon2 = new ImageIcon("images/cyan-ball.gif");
// Create the buttons
btnImage1 = new JButton("First Button", btnIcon1);
// Assign hot key for the button label
btnImage1.setMnemonic(KeyEvent.VK_F);
btnImage1.setActionCommand("first");
btnImage2 = new JButton("Second button", btnIcon2);
btnImage2.setMnemonic(KeyEvent.VK_S);
btnImage2.setActionCommand("second");
// Register the butttons with the ActionListener
ActionListener listener = new ActionHandler();
btnImage1.addActionListener(listener);
btnImage2.addActionListener(listener);
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JButton Example (contd)
add(btnImage1); 
add(btnImage2);
}
class ActionHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
// If first button clicked
if (e.getActionCommand().equals("first")) {
message = "You like Red Balls!";
} else if (e.getActionCommand().equals("second")) {
message = "You like Cyan Balls!";
} 
repaint();
}
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawString(message, 100, 150);
}
}
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JButton Example (contd)
Output
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JCheckbox
Checkbox is used to provide the user with a set of 
options.
JCheckBox class has the following constructors:
JCheckBox()
JCheckBox(Icon icon)
JCheckBox(Icon icon, boolean selected)
JCheckBox(String text)
JCheckBox(String text, boolean selected)
JCheckBox(String text, Icon icon)
JCheckBox(String text, Icon icon, boolean 
selected)
JCheckBox(Action a)
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JCheckbox Example
public class CheckBoxDemo extends JPanel {
JCheckBox chinButton, glassesButton, hairButton, teethButton;
StringBuffer choices;
JLabel pictureLabel;
public CheckBoxDemo() {
// Create the check boxes
chinButton = new JCheckBox("Chin");
chinButton.setMnemonic(KeyEvent.VK_C);
chinButton.setSelected(true);
glassesButton = new JCheckBox("Glasses");
glassesButton.setMnemonic(KeyEvent.VK_G);
glassesButton.setSelected(true);
hairButton = new JCheckBox("Hair");
hairButton.setMnemonic(KeyEvent.VK_H);
hairButton.setSelected(true);
teethButton = new JCheckBox("Teeth");
teethButton.setMnemonic(KeyEvent.VK_T);
teethButton.setSelected(true);
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JCheckbox Example (contd)
// Register a listener for the check boxes.
CheckBoxListener myListener = new CheckBoxListener();
chinButton.addItemListener(myListener);
glassesButton.addItemListener(myListener);
hairButton.addItemListener(myListener);
teethButton.addItemListener(myListener);
// Indicates what's on the geek.
choices = new StringBuffer("cght");
// Set up the picture label
pictureLabel = new JLabel(new ImageIcon("images/geek/geek-"
+ choices.toString() + ".gif"));
pictureLabel.setToolTipText(choices.toString());
// Put the check boxes in a column in a panel
JPanel checkPanel = new JPanel();
checkPanel.setLayout(new GridLayout(0, 1));
checkPanel.add(chinButton); checkPanel.add(glassesButton);
checkPanel.add(hairButton); checkPanel.add(teethButton);
setLayout(new BorderLayout());
add(checkPanel, BorderLayout.WEST);
add(pictureLabel, BorderLayout.CENTER);
setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
}
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JCheckbox Example (contd)
/** Listens to the check boxes. */
class CheckBoxListener implements ItemListener {
public void itemStateChanged(ItemEvent e) {
int index = 0; char c = '-';
Object source = e.getSource();
if (source == chinButton) {
index = 0; c = 'c';
} else if (source == glassesButton) {
index = 1; c = 'g';
} else if (source == hairButton) {
index = 2; c = 'h';
} else if (source == teethButton) {
index = 3; c = 't';
}
if (e.getStateChange() == ItemEvent.DESELECTED)
c = '-';
choices.setCharAt(index, c);
pictureLabel.setIcon(new ImageIcon("images/geek/geek-"
+ choices.toString() + ".gif"));
pictureLabel.setToolTipText(choices.toString());
}
}
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JCheckbox Example (contd)
Output
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JRadiobutton
A set of radio buttons displays a number of options out of which 
only one may be selected.
A ButtonGroup is used to create a group in Swing.
JRadioButton object can be created by using:
JRadioButton()
JRadioButton(Icon icon)
JRadioButton(Icon, boolean selected)
JRadioButton(String text)
JRadioButton(String text, boolean selected)
JRadioButton(String text, Icon icon)
JRadioButton(String text, Icon icon, boolean selected)
JRadioButton(Action a)
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JRadio Example
public class RadioButtonDemo extends JPanel {
static JFrame frame;
static String birdString = "Bird";
static String catString = "Cat";
static String dogString = "Dog";
static String rabbitString = "Rabbit";
static String pigString = "Pig";
JLabel picture;
public RadioButtonDemo() {
// Create the radio buttons.
JRadioButton birdButton = new JRadioButton(birdString);
birdButton.setMnemonic(KeyEvent.VK_B);
birdButton.setActionCommand(birdString);
birdButton.setSelected(true);
JRadioButton catButton = new JRadioButton(catString);
catButton.setMnemonic(KeyEvent.VK_C);
catButton.setActionCommand(catString);
JRadioButton dogButton = new JRadioButton(dogString);
dogButton.setMnemonic(KeyEvent.VK_D);
dogButton.setActionCommand(dogString);
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JRadio Example (contd)
JRadioButton rabbitButton = new JRadioButton(rabbitString);
rabbitButton.setMnemonic(KeyEvent.VK_R);
rabbitButton.setActionCommand(rabbitString);
JRadioButton pigButton = new JRadioButton(pigString);
pigButton.setMnemonic(KeyEvent.VK_P);
pigButton.setActionCommand(pigString);
// Group the radio buttons.
ButtonGroup group = new ButtonGroup();
group.add(birdButton);
group.add(catButton);
group.add(dogButton);
group.add(rabbitButton);
group.add(pigButton);
// Register a listener for the radio buttons.
RadioListener myListener = new RadioListener();
birdButton.addActionListener(myListener);
catButton.addActionListener(myListener);
dogButton.addActionListener(myListener);
rabbitButton.addActionListener(myListener);
pigButton.addActionListener(myListener);
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JRadio Example (contd)
// Set up the picture label
picture = new JLabel(new ImageIcon
("images/" + birdString + ".gif"));
picture.setPreferredSize(new Dimension(177, 122));
// Put the radio buttons in a column in a panel
JPanel radioPanel = new JPanel();
radioPanel.setLayout(new GridLayout(0, 1));
radioPanel.add(birdButton);
radioPanel.add(catButton);
radioPanel.add(dogButton);
radioPanel.add(rabbitButton);
radioPanel.add(pigButton);
setLayout(new BorderLayout());
add(radioPanel, BorderLayout.WEST);
add(picture, BorderLayout.CENTER);
setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
}
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JRadio Example (contd)
/** Listens to the radio buttons. */
class RadioListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
picture.setIcon(new ImageIcon("images/" + 
e.getActionCommand() + ".gif"));
}
}
public static void main(String s[]) {
frame = new JFrame("RadioButtonDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane()
.add(new RadioButtonDemo(), BorderLayout.CENTER);
frame.pack();
frame.setVisible(true);
}
}
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JRadio Example (contd)
Output
4/7/2018  84
JList
When the options to choose from is large, the user 
can be presented with a list to choose .
JList component arranges elements one after the 
other, which can be selected individually or in a 
group.
JList class can display strings as well as icons.
JList does not provide support for double clicks.
MouseListener can be used to overcome the 
double click problem.
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JList (contd)
•public JList() – constructs a JList with an empty 
model.
•public JList(ListModel dataModel) –
displays the elements in the specified, non-null list 
model.
•public JList(Object[] listData) – displays 
the elements of the specified array “listData”.
•JList does not support scrolling. To enable scrolling, 
the following piece of code can be used:
JScrollPane myScrollPane = new JScrollPane();
myScrollPane.getViewport().setView(dataList);
Or 
JScrollPane myScrollPane = new JScrollPane(dataList);
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JList Example (contd)
class AllStars extends JFrame implements ListSelectionListener {
String stars[] = {"Antonio Banderas", "Leonardo DiCaprio", 
"Sandra Bullock", "Hugh Grant", "Julia Roberts" };
JList lstMovieStars = new JList(stars);
JLabel lblQuestion = new JLabel("Who is your favorite movie star?");
JTextField txtMovieStar = new JTextField(30);
public AllStars(String str) {
super(str);
JPanel lstPanel = (JPanel) getContentPane();
lstPanel.setLayout(new BorderLayout());
lstPanel.add(lblQuestion, BorderLayout.NORTH);
lstMovieStars.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
lstMovieStars.setSelectedIndex(0);
// register selection listener
lstMovieStars.addListSelectionListener(this);
lstMovieStars.setBackground(Color.LIGHT_GRAY);
lstMovieStars.setForeground(Color.BLUE);
lstPanel.setBackground(Color.WHITE);
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JList Example (contd)
lstPanel.setForeground(Color.BLACK);
lstPanel.add("Center", new JScrollPane(lstMovieStars));
lstPanel.add(txtMovieStar, BorderLayout.SOUTH);
}
// implement selection listener method
public void valueChanged(ListSelectionEvent e) {
if (e.getValueIsAdjusting() == false) {
if (lstMovieStars.getSelectedIndex() != -1) {
txtMovieStar.setText(
(String) lstMovieStars.getSelectedValue());
}
}
}
public static void main(String args[]) {
AllStars allStars = new AllStars("A sky full of stars!");
allStars.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
allStars.setSize(300, 300);
allStars.setVisible(true);
}
}
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JList Example (contd)
Output
4/7/2018  89
JComboBox
Combination of text field and drop-down list.
In Swing, combo box is represented by JComboBox
class.
public JComboBox() – this constructor creates a 
JComboBox with a default data model.
public JComboBox(ComboBoxModel asModel) –
a combo box that takes its items from an existing 
ComboBoxModel.
public JComboBox(Object[] items) – a combo 
box that contains the elements of the specified array.
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JComboBox Example
class BestSeller extends JFrame implements ItemListener {
String names[] = { "Frederick Forsyth", "John Grisham",
"Mary Higgins Clarke", "Patricia Cornwell" };
JComboBox authors = new JComboBox(names);
public BestSeller(String str) {
super(str);
JPanel bestPane = (JPanel) getContentPane();
bestPane.setLayout(new BorderLayout());
authors.addItemListener(this);
authors.setBackground(Color.LIGHT_GRAY);
authors.setForeground(Color.BLACK);
bestPane.setForeground(Color.BLACK);
bestPane.add(authors, BorderLayout.PAGE_START);
}
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JComboBox Example (contd)
public void itemStateChanged(ItemEvent e) {
if (e.getStateChange() == ItemEvent.SELECTED) {
System.out.println((String) e.getItem());
}
}
public static void main(String args[]) {
BestSeller author = new BestSeller("BestSellers!");
author.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
author.setSize(200, 200);
author.setVisible(true);
}
}
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JComboBox Example (contd)
Output
4/7/2018  93
Summary
The Java Foundation Classes (JFC) are developed as an 
extension to Abstract Windows Toolkit (AWT), to 
overcome the shortcomings of AWT.
Swing is a set of classes under the JFC that provide 
lightweight visual components and enable creation of 
an attractive GUI. 
Swing Applets provide support for assistive 
technologies and a RootPane (and thus support for 
adding menubar).
With Swing, most of the components can display text 
as well as images.