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COS240 O-O Languages
AUBG, COS dept
Lecture 11
Title:
Java and Event-Driven
Programming
Reference: COS240 Syllabus
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
1
Lecture Contents:











To describe events, event sources, and event classes.
To define listener classes, register listener objects with the source
object, and write the code to handle events.
To define listener classes using inner classes.
To define listener classes using anonymous inner classes.
To explore various coding styles for creating and registering
listeners.
To get input from text field upon clicking a button.
To write programs to deal with WindowEvent.
To simplify coding for listener classes using listener interface
adapters.
To write programs to deal with MouseEvent.
To write programs to deal with KeyEvent.
To use the javax.swing.Timer class to control animations
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
2
Motivations
Suppose you wish to write a GUI program that lets user enter
the loan amount, annual interest rate, & number of years, and
click the Compute Loan button to obtain the monthly
payment and total payment. How do you accomplish the
task? You have to use event-driven programming to write the
code to respond to the button-clicking event.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
3
Motivations
Suppose you wish to write a program that animates
a rising flag, as shown in Figures below. How do
you accomplish the task? An effective way to solve
it is to use a timer in event-driven programming,
which is the subject of this lecture.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
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Procedural vs. Event-Driven
Programming
 Procedural
programming is executed in
procedural order.
 In
event-driven programming, code is executed
upon activation of events.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
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5
Event-Driven Programming
Practical Demo Introduction
Example: the ActionListener Interface
(open file ProgDemoEvH1.java)
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
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To feel Event-Driven Programming
 The
case:
 3 buttons (OK, Cancel, Exit) placed into a panel.
 Panel placed into a frame.
 The program displays 3 buttons in the frame.
 A message is displayed on the console and into a
message box when a button is clicked.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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
To respond to a button click, you must write the code to
process the button-clicking action

The button is a source object where the action originates.

You need to create an object capable of handling the
action event on a button. This object is called a listener.

Button ------------------ Event ------------------ Listener
↑
Clicking
Button fires
action event
↑
An event
is an object
↑
Listener object
processes the
event
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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How to understand source & listener
Source is an object, like component button
 To be a listener:

– The object must be instance of the ActionListener
interface. You need a user class to implement the
interface ( method actionPeformed() ) and to
create object of your user defined class.
– The object created as a listener must be registered with
(i.e. to bind it to) the source using method
source.addListener(listener)
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
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How to understand source & listener
You have to follow a sequence of four steps:
A: create a component – source of an event
B: develop user defined class that implements
ActionListener interface
C: create an instance of user defined class above in
section B.
D: bind action listener /object from section C/ with the
source of the event /object from section A/
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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How to understand source & listener
// Create a button with text OK
JButton jbtOK1 = new JButton("OK");
// creating listener as object/instance
OK1ListenerClass listenerOK = new OK1ListenerClass();
// registering listener, i.e. binding listener by component
jbtOK1.addActionListener(listenerOK);
// user specified class to implement interface
class OK1ListenerClass implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("OK button clicked" );
JOptionPane.showMessageDialog(null,"OK button clicked");
} // end of method
} // end of class
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
11
How to understand source & listener
// Create a button with text OK
JButton jbtOK1 = new JButton("OK");
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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How to understand source & listener
// Create a button with text OK
JButton jbtOK1 = new JButton("OK");
// user specified class to implement interface
class OK1ListenerClass implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("OK button clicked" );
JOptionPane.showMessageDialog(null,"OK button clicked");
} // end of method
} // end of class
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
13
How to understand source & listener
// Create a button with text OK
JButton jbtOK1 = new JButton("OK");
// creating listener as object/instance
OK1ListenerClass listenerOK = new OK1ListenerClass();
// user specified class to implement interface
class OK1ListenerClass implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("OK button clicked" );
JOptionPane.showMessageDialog(null,"OK button clicked");
} // end of method
} // end of class
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
14
How to understand source & listener
// Create a button with text OK
JButton jbtOK1 = new JButton("OK");
// creating listener as object/instance
OK1ListenerClass listenerOK = new OK1ListenerClass();
// registering listener, i.e. binding listener by component
jbtOK1.addActionListener(listenerOK);
// user specified class to implement interface
class OK1ListenerClass implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("OK button clicked" );
JOptionPane.showMessageDialog(null,"OK button clicked");
} // end of method
} // end of class
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
15
The ActionListener Interface
and Handling GUI Events
Source object (e.g., button)
Listener object contains a method for
processing the event.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Trace Execution
public class HandleEvent extends JFrame {
public HandleEvent() {
…
OKListenerClass listener1 = new OKListenerClass();
jbtOK.addActionListener(listener1);
…
}
public static void main(String[] args) {
…
}
}
class OKListenerClass implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("OK button clicked");
}
}
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
17
Event-Driven Programming
Comprehensive Introduction
.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
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Java uses a delegation-based model for event
handling:
a source object fires an event;
an object interested in the event, handles it
Button --------------------- Event ------------------- Listener
↑
Clicking
Button fires
action event
↑
An event
is an object
↑
Listener object
processes the
event
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Event Source
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Event Source
 The
component that creates an event and
fires it, is called
– Source object or
– Source component
 E.g.
a button is a source object for a buttonclicking action event
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rights reserved. 0132130807
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Events
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Events
An event can be defined as a type of signal to the
program that something has happened.
The event is generated
– by external user actions such as mouse movements, mouse
clicks, and keystrokes,
OR
– by the operating system, such as a timer.
 An
event is an instance of EventObject class.
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rights reserved. 0132130807
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Event Classes
EventObject
AWTEvent
ActionEvent
ContainerEvent
AdjustmentEvent
FocusEvent
ComponentEvent
InputEvent
ItemEvent
PaintEvent
TextEvent
WindowEvent
MouseEvent
KeyEvent
ListSelectionEvent
ChangeEvent
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Event Information
An event object contains whatever properties are
pertinent to the event. You can identify the source
object of the event using the getSource()
instance method in the EventObject class. The
subclasses of EventObject deal with special
types of events, such as button actions, window
events, component events, mouse movements, and
keystrokes. Table on next page lists external user
actions, source objects, and event types generated.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Selected User Actions
Source
Object
User Action
Event Type
Generated
Click a button
Click a check box
Click a radio button
JButton
JCheckBox
JRadioButton
ActionEvent
ItemEvent, ActionEvent
ItemEvent, ActionEvent
Press return on a text field
JTextField
ActionEvent
Select a new item
Window opened, closed, etc.
Mouse pressed, released, etc.
JComboBox
Window
Component
ItemEvent, ActionEvent
WindowEvent
MouseEvent
Key released, pressed, etc.
Component
KeyEvent
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rights reserved. 0132130807
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Listeners, Registrations, and
Handling Events
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Java and EvH

Java uses delegation-based model for EvH:
– A source object fires an event, and
– An object, interested in the event, handles it. The object
is called listener.

For an object to be a listener for an event on a
source object, two requirements must meet:
– The object must be instance of the corresponding eventlistener interface. You need a user class to implement
the interface and to create object of your user defined
class.
– The listener object created must be registered by (i.e. to
bind it to) the source using method like
source.addListener(listener)
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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The Delegation Model
Trigger an event
source: SourceClass
User
Action
XListener
+addXListener(listener: XListener)
(a) A generic source component
with a generic listener
+handler(event: XEvent)
Register by invoking
source.addXListener(listener);
listener: ListenerClass
source: JButton
ActionListener
+addActionListener(listener: ActionListener)
+actionPerformed(event: ActionEvent)
(b) A JButton source component
with an ActionListener
Register by invoking
source.addActionListener(listener);
listener: CustomListenerClass
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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The Delegation Model: Example
JButton jbt = new JButton("OK");
ActionListener listener = new OKListener();
jbt.addActionListener(listener);
Comment: when you click the button,
the JButton source object (jbt) fires an ActionEvent event
and passes it to invoke the listener’s actionPerformed() method
to handle the event
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Selected Event Handlers
Event Class
Listener Interface
Listener Methods (Event Handlers)
ActionEvent
ItemEvent
WindowEvent
ActionListener
ItemListener
WindowListener
ContainerEvent
ContainerListener
MouseEvent
MouseListener
KeyEvent
KeyListener
actionPerformed(ActionEvent)
itemStateChanged(ItemEvent)
windowClosing(WindowEvent)
windowOpened(WindowEvent)
windowIconified(WindowEvent)
windowDeiconified(WindowEvent)
windowClosed(WindowEvent)
windowActivated(WindowEvent)
windowDeactivated(WindowEvent)
componentAdded(ContainerEvent)
componentRemoved(ContainerEvent)
mousePressed(MouseEvent)
mouseReleased(MouseEvent)
mouseClicked(MouseEvent)
mouseExited(MouseEvent)
mouseEntered(MouseEvent)
keyPressed(KeyEvent)
keyReleased(KeyEvent)
keyTyped(KeyEvent)
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java.awt.event.ActionEvent
java.util.EventObject
+getSource(): Object
Returns the object on which the event initially occurred.
java.awt.event.AWTEvent
java.awt.event.ActionEvent
+getActionCommand(): String
Returns the command string associated with this action. For a
button, its text is the command string.
+getModifiers(): int
Returns the modifier keys held down during this action event.
+getWhen(): long
Returns the timestamp when this event occurred. The time is
the number of milliseconds since January 1, 1970, 00:00:00
GMT.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Demo program

Open file ProgDemoEvH1.java
– Examine the source text

Three buttons, three classes to implement
interface ActionListener, three listeners objects
registered to the buttons
– Compile
– Run

Output – mixture of console output and
showMessageDialog
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
33
Demo program

Open file ProgDemoEvH1.java

Examine the source text
Modify the program on your choice
 Call ActionEvent methods like

– getSource()
– getActionCommand()
– getWhen()
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
34
Demo program

Open file ProgDemoMouseEvents.java
– Examine the source text

Panel into a frame, one user defined class to
implement interface MouseListener and all its
methods, one listener object registered to the panel
– Compile
– Run

Output – console output
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
35
MouseEvent
java.awt.event.InputEvent
+getWhen(): long
Returns the timestamp when this event occurred.
+isAltDown(): boolean
Returns whether or not the Alt modifier is down on this event.
+isControlDown(): boolean
Returns whether or not the Control modifier is down on this event.
+isMetaDown(): boolean
Returns whether or not the Meta modifier is down on this event
+isShiftDown(): boolean
Returns whether or not the Shift modifier is down on this event.
java.awt.event.MouseEvent
+getButton(): int
Indicates which mouse button has been clicked.
+getClickCount(): int
Returns the number of mouse clicks associated with this event.
+getPoint(): java.awt.Point
Returns a Point object containing the x and y coordinates.
+getX(): int
Returns the x-coordinate of the mouse point.
+getY(): int
Returns the y-coordinate of the mouse point.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
36
Handling Mouse Events

Java provides two listener interfaces,
MouseListener and MouseMotionListener,
to handle mouse events.

The MouseListener listens for actions such as
when the mouse is pressed, released, entered,
exited, or clicked.

The MouseMotionListener listens for
actions such as dragging or moving the
mouse.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Handling Mouse Events
java.awt.event.MouseListener
+mousePressed(e: MouseEvent): void
Invoked when the mouse button has been pressed on the
source component.
+mouseReleased(e: MouseEvent): void
Invoked when the mouse button has been released on the
source component.
+mouseClicked(e: MouseEvent): void
Invoked when the mouse button has been clicked (pressed and
released) on the source component.
+mouseEntered(e: MouseEvent): void
Invoked when the mouse enters the source component.
+mouseExited(e: MouseEvent): void
Invoked when the mouse exits the source component.
java.awt.event.MouseMotionListener
+mouseDragged(e: MouseEvent): void
Invoked when a mouse button is moved with a button pressed.
+mouseMoved(e: MouseEvent): void
Invoked when a mouse button is moved without a button
pressed.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
38
Demo program
 Open
file ProgDemoMouseEvents.java
 Examine
the source text
 Modify
the program on your choice
 Call some MouseEvent methods (details
before 3 slides)
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
39
Demo program

Open file ProgDemoKeyEvents.java
– Examine the source text

Panel into a frame, one user defined class to
implement interface KeyListener and all its
methods, one listener object registered to the panel
– Compile
– Run

Output – console output and graphic output
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
40
Inner Class Listeners
A listener class is designed specifically to
create a listener object for a GUI
component (e.g., a button). It will not be
shared by other applications. So, it is
appropriate to define the listener class
inside the frame class as an inner class.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
41
Inner Classes
Inner class: A class is a member of another class.
Advantages: In some applications, you can use an
inner class to make programs simple.

An inner class can reference the data and
methods defined in the outer class in which it
nests, so you do not need to pass the reference
of the outer class to the constructor of the inner
class.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
42
Inner Classes, cont.
public class Test {
...
}
// OuterClass.java: inner class demo
public class OuterClass {
private int data;
/** A method in the outer class */
public void m() {
// Do something
}
public class A {
...
}
(a)
// An inner class
class InnerClass {
/** A method in the inner class */
public void mi() {
// Directly reference data and method
// defined in its outer class
data++;
m();
}
}
public class Test {
...
// Inner class
public class A {
...
}
}
(b)
}
(c)
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
43
Inner Classes (cont.)
 Inner
classes can make programs simple and
concise.
 An
inner class supports the work of its
containing outer class and is compiled into a
class named
OuterClassName$InnerClassName.class. For
example, the inner class InnerClass in
OuterClass is compiled into
OuterClass$InnerClass.class.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
44
Inner Classes (cont.)
 An
inner class can be declared public,
protected, or private subject to the same
visibility rules applied to a member of the
class.
 An
inner class can be declared static. A
static inner class can be accessed using
the outer class name. A static inner class
cannot access nonstatic members of the
outer class
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
45
Demo program
 Open
file ProgDemoKeyEvents.java
 Examine
 Modify
the source text
the program on your choice
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
46
Handling Keyboard Events
To process a keyboard event, use the following
handlers in the KeyListener interface:

keyPressed(KeyEvent e)
Called when a key is pressed.

keyReleased(KeyEvent e)
Called when a key is released.

keyTyped(KeyEvent e)
Called when a key is pressed and then
released.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
47
The KeyEvent Class

Methods:
getKeyChar() method
getKeyCode() method

Keys:
Home
End
Page Up
Page Down
etc...
VK_HOME
VK_END
VK_PGUP
VK_PGDN
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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The KeyEvent Class, cont.
java.awt.event.InputEvent
java.awt.event.KeyEvent
+getKeyChar(): char
Returns the character associated with the key in this event.
+getKeyCode(): int
Returns the integer keyCode associated with the key in this event.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
49
Demo program

Open file ProgDemoControlRectangle.java
– Examine the source text

Three buttons, three classes to implement
interface ActionListener and its EvHandler
method ActionPerformed(), three listeners
objects registered to the buttons
– Compile
– Run

Output – console output and graphics output
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
50
Ideas to modify this demo
Circle instead of rectangle.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
51
Demo program
 Open
file ProgDemoControlRectangle.java
 Examine
 Modify
the source text
the program on your choice
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
52
Demo program

Open file ProgDemoWindowEvents.java
– Examine the source text

Panel into a frame, one user defined class to
implement interface WindowListener and all its
seven methods, one listener object registered to
the entire frame or window
– Compile
– Run

Output – console output
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
53
Demonstrate: Handling Window Events

Objective: Any subclass of the Window class can
generate the following window events:
 window opened,


window closing,
window closed,

window activated,
window deactivated,

window iconified,
window deiconified.
This program creates a frame, listens to the window
events, and displays a message to indicate the occurring
event.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
54
Demo program
 Open
file ProgDemoWindowEvents.java
 Examine
 Modify
the source text
the program on your choice
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
55
Demo program

Open file ProgDemoWindowEventsVer2.java
– Examine the source text

Panel into a frame, one user defined class to
implement interface WindowListener and all its
seven methods, one anonymous listener object
registered to the entire frame or window
– Compile
– Run

Output – console output
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
56
Anonymous Inner Classes




An anonymous inner class must always extend a superclass or
implement an interface, but it cannot have an explicit extends or
implements clause.
An anonymous inner class must implement all the abstract
methods in the superclass or in the interface.
An anonymous inner class always uses the no-arg constructor
from its superclass to create an instance. If an anonymous inner
class implements an interface, the constructor is Object().
An anonymous inner class is compiled into a class named
OuterClassName$n.class. For example, if the outer class Test
has two anonymous inner classes, these two classes are
compiled into Test$1.class and Test$2.class.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
57
Anonymous Inner Classes (cont.)
Inner class listeners can be shortened using anonymous
inner classes. An anonymous inner class is an inner
class without a name. It combines declaring an inner
class and creating an instance of the class in one step.
An anonymous inner class is declared as follows:
new SuperClassName/InterfaceName() {
// Implement or override methods in superclass or interface
// Other methods if necessary
}
AnonymousListenerDemo
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
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Alternative Ways of Defining
Listener Classes
There are many other ways to define the listener
classes. For example, you may rewrite Listing
with separate listener objects from separate
listener classes by creating just one listener,
register the listener with the buttons, and let the
listener detect the event source, i.e., which
button fires the event.
DetectSourceDemo
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
59
Alternative Ways of Defining
Listener Classes
You may also define the custom frame class that
implements ActionListener.
FrameAsListenerDemo
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
60
Demo program
 Open
file ProgDemoWindowEventsVer2.java
 Examine
 Modify
the source text
the program on your choice
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
61
Demo program
 Open
file ProgDemoTimerRectangle.java
– Examine the source text
– Compile
– Run
 Output
– graphics output
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
62
The Timer Class
Some non-GUI components can fire events. The javax.swing.Timer
class is a source component that fires an ActionEvent at a predefined
rate.
javax.swing.Timer
+Timer(delay: int, listener:
ActionListener)
Creates a Timer with a specified delay in milliseconds and an
ActionListener.
+addActionListener(listener:
ActionListener): void
Adds an ActionListener to the timer.
+start(): void
Starts this timer.
+stop(): void
Stops this timer.
+setDelay(delay: int): void
Sets a new delay value for this timer.
The Timer class can be used to control animations. For example, you
can use it to display a moving message.
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
63
Demo program
 Open
file ProgDemoTimerRectangle.java
 Examine
 Modify
the source text
the program on your choice
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All
rights reserved. 0132130807
64
Thank You
for
Your attention!
Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807
65