Download Chapter 12 Applets and Advanced Graphics

Chapter 14 Applets, Images, and Audio
Prerequisites for Part III
Chapter 8 Inheritance and Polymorphism
Chapter 9 Abstract Classes and Interfaces
Chapter 11 Getting Started with GUI Programming
Chapter 12 Event-Driven Programming
愿生如夏花之绚烂，死如秋叶之静美---- 泰戈尔
Chapter 13 Creating User Interfaces
Chapter 14 Applets, Images, Audio
Liang,Introduction to Java Programming,revised by Dai-kaiyu
1
Objectives











To explain how the Web browser controls and executes applets (§ 14.2).
To describe the init, start, stop, and destroy methods in the Applet class (§
14.2).
To know how to embed applets in Web pages (§ 14.4).
To run applets from appletviewer and from Web browsers (§ 14.4).
To pass string values to applets from HTML (§ 14.5).
To write a Java program that can run as both an application and an applet (§
14.6).
To get image files using the URL class and display images in the panel (§
14.9 Optional).
To develop a reusable component ImageViewer to display images (§ 14.10
Optional).
To get audio files and play sound (§ 14.12 Optional).
To package and deploy Java projects using Java archive files (§ 14.13
Optional).
To use Swing pluggable look-and-feel (§ 14.14 Optional).
2
Liang,Introduction to Java Programming,revised by Dai-kaiyu
Introduction
Applet
Program that runs in Applet Container
appletviewer (test utility for applets)
Web browser (IE, Communicator)
Executes when HTML (Hypertext Markup
Language) document containing applet is opened
and downloaded
Applications run in command windows
Liang,Introduction to Java Programming,revised by Dai-kaiyu
3
Launching applets
 Applications are
started by a call to the
main method
 Applets have no main
method
 Class file referenced in
the HTML document
 Browser loads and
runs the Applet
 JDK includes the
appletviewer
application
Liang,Introduction to Java Programming,revised by Dai-kaiyu
4
The TicTacToe Applet
You start as player "X"
Fig. 3.2
Sample execution of the TicTacToe applet.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
5
The DrawTest Applet
Fig. 3.4
Sample execution of applet DrawTest.
Radio
button
Combo
Box
Liang,Introduction to Java Programming,revised by Dai-kaiyu
6
The Applet Class
public class MyApplet extends java.applet.Applet {
...
/** The no-arg constructor is called by the browser when the Web
page containing this applet is initially loaded, or reloaded
*/
public MyApplet() {
...
}
/** Called by the browser after the applet is loaded
*/
public void init() {
...
}
/** Called by the browser after the init() method, or
every time the Web page is visited
*/
public void start() {
...
}
/** Called by the browser when the page containing this
applet becomes inactive
*/
public void stop() {
...
}
/** Called by the browser when the Web browser exits */
public void destroy() {
...
}
Liang,Introduction to Java Programming,revised by Dai-kaiyu
/** Other methods if necessary... */
}
7
The Applet Class, cont.
When the applet is loaded, the Web browser creates an
instance of the applet by invoking the applet’s no-arg
constructor.
 The browser uses the init, start, stop, and destroy
methods to control the applet. By default, these methods do
nothing. To perform specific functions, they need to be
modified in the user's applet so that the browser can call
your code properly.
See figure14.1 (a) in textbook
Liang,Introduction to Java Programming,revised by Dai-kaiyu
8
11.4.2 Applet lifecycle methods
 init(), start(), stop(),
destroy()
 init() is called when
the applet is loaded
 start() is called by
init, and when the
user returns to the
page
 stop() is called when
the user leaves the
page
 destroy() is called
when the browser is
closed
Liang,Introduction to Java Programming,revised by Dai-kaiyu
9
Browser Calling Applet Methods
Loaded
JVM loads the
applet class
Browser creates
the applet
Created
Browser
invokes init()
Initialized
Browser
invokes start()
Browser
invokes stop()
Started
Stopped
Browser
invokes stop()
Browser invokes
destroy()
Destroyed
Liang,Introduction to Java Programming,revised by Dai-kaiyu
10
The init() Method
Invoked when the applet is first loaded and again if
the applet is reloaded.
A subclass of Applet should override this method if the
subclass has an initialization to perform.
 The functions usually implemented in this method
include creating new threads, loading images, setting up
user-interface components, and getting string parameter
values from the <applet> tag in the HTML page.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
11
The start() Method
Invoked after the init() method is executed; also called
whenever the applet becomes active again after a period of
inactivity (for example, when the user returns to the page
containing the applet after surfing other Web pages).
A subclass of Applet overrides this method if it has
any operation that needs to be performed whenever
the Web page containing the applet is visited. An
applet with animation, for example, might use the
start method to resume animation.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
12
The stop() Method
The opposite of the start() method, which is called when the user
moves back to the page containing the applet; the stop() method is
invoked when the user moves off the page.
A subclass of Applet overrides this method if it has any
operation that needs to be performed each time the Web
page containing the applet is no longer visible. When the
user leaves the page, any threads the applet has started
but not completed will continue to run. You should
override the stop method to suspend the running threads
so that the applet does not take up system resources when
it is inactive.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
13
The destroy() Method
Invoked when the browser exits normally to
inform the applet that it is no longer needed and
that it should release any resources it has allocated.
A subclass of Applet overrides this method if it
has any operation that needs to be performed
before it is destroyed. Usually, you won't need to
override this method unless you wish to release
specific resources, such as threads that the applet
created.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
14
applet methods
 Applet methods
are called by the
browser
 Different browser
events result in
calls to the
methods
Liang,Introduction to Java Programming,revised by Dai-kaiyu
15
The JApplet Class
The Applet class is an AWT class and is not designed to
work with Swing components.
To use Swing components in Java applets, it is necessary to
create a Java applet that extends javax.swing.JApplet, which
is a subclass of java.applet.Applet.
JApplet inherits all the methods from the Applet class. In
addition, it provides support for laying out Swing
components.
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First Simple Applet
// WelcomeApplet.java: Applet for displaying a message
import javax.swing.*;
public class WelcomeApplet extends JApplet {
/** Initialize the applet */
public void init() {
getContentPane().add(new JLabel("Welcome to Java",
JLabel.CENTER));
}
}
Liang,Introduction to Java Programming,revised by Dai-kaiyu
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First Simple Applet
<html>
<head>
<title>Welcome Java Applet</title>
</head>
<body>
<applet
code = "WelcomeApplet.class"
width = 350
height = 200>
</applet>
</body>
</html>
WelcomeApplet
Run Applet Viewer18
Liang,Introduction to Java Programming,revised by Dai-kaiyu
Writing Applets
 Always extends the JApplet class, which is a
subclass of Applet for Swing components.
 Override init(), start(), stop(), and destroy() if
necessary. By default, these methods are empty.
 Add your own methods and data if necessary.
 Applets are always embedded in an
HTML page.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
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The <applet> HTML Tag
<applet
code=classfilename.class
width=applet_viewing_width_in_pixels
height=applet_viewing_height_in_pixels
[archive=archivefile]
[codebase=applet_url]
[vspace=vertical_margin]
[hspace=horizontal_margin]
[align=applet_alignment]
[alt=alternative_text]
>
<param name=param_name1
value=param_value1>
</applet>
Liang,Introduction to Java Programming,revised by Dai-kaiyu
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Example 14.1 Using Applets
Objective: Compute
Loans. The applet enables
the user to enter the
annual interest rate, the
number of years, and the
loan amount. Click the
Compute Loan button,
and the applet displays
the monthly payment and
the total payment.
LoanApplet
Run Applet Viewer21
Liang,Introduction to Java Programming,revised by Dai-kaiyu
Passing Parameters to Applets
<applet
code = "DisplayMessage.class"
width = 200
height = 50>
<param name=MESSAGE value="Welcome to Java">
<param name=X value=20>
<param name=Y value=20>
alt="You must have a Java-enabled browser to view the
applet"
</applet>
Liang,Introduction to Java Programming,revised by Dai-kaiyu
22
Example 14.2 Passing Parameters to
Java Applets
Objective: Display a
message at a
specified location.
The message and the
location (x, y) are
obtained from the
HTML source.
DisplayMessage
Run Applet Viewer23
Liang,Introduction to Java Programming,revised by Dai-kaiyu
Applications vs. Applets
 Similarities
Since they both are subclasses of the Container class, all the user
interface components, layout managers, and event-handling features
are the same for both classes.
 Differences
Applications are invoked from the static main method by the Java
interpreter, and applets are run by the Web browser. The Web
browser creates an instance of the applet using the applet’s no-arg
constructor and controls and executes the applet through the init,
start, stop, and destroy methods.
Applets have security restrictions
Web browser creates graphical environment for applets, GUI
applications are placed in a frame.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
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Security Restrictions on Applets
 Applets are not allowed to read from, or write to,
the file system of the computer viewing the
applets.
 Applets are not allowed to run any programs on
the browser’s computer.
 Applets are not allowed to establish connections
between the user’s computer and another
computer except with the server where
the applets are stored.
Excute
Liang,Introduction to Java Programming,revised by Dai-kaiyu
25
Conversions Between Applications
and Applets
 Conversions between applications and applets are
simple and easy.
 You can always convert an applet into an application.
 You can convert an application to an
applet as long as security restrictions are
not violated.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
26
Example 14.3
Running a Program as an Applet
and as an Application
 Objective: Modify MessageApplet to enable it to run
both as an applet and as an application.
DisplayMessageApp
Run as Application
Run as Applet
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27
Optional
Case Study: TicTacToe
JPanel
-char token
+getToken
+setToken
-token: char
+paintComponet
+mouseClicked
+getToken():char
MouseListener
-char token
Cell +getToken
+setToken
+paintComponet
+mouseClicked
Token used in the cell (default: ' ').
Returns the token in the cell.
+setToken(token: char): void
Sets a new token in the cell.
#paintComponent(g: Graphics): void
Paints the token in the cell.
+mouseClicked(e: MouseEvent): void
Handles a mouse click on the cell.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
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Case Study: TicTacToe, cont.
Cell
JApplet
9 token
-char
-char token
1
+getToken
+setToken
+paintComp
onet
+mouseClic
ked
+getToken
TicTacToe
+setToken
+paintComp
-whoseTurn:
char
onet
-cell: Cell[][]
+mouseClic
ked
-jlblStatus:
JLabel
Indicates which player has the turn, initially 'X'.
+TicTacToe()
Constructs the TicTacToe user interface.
+isFull(): boolean
Returns true if all cells are filled.
+isWon(token: char): boolean
Returns true if a player with the specified token has won.
TicTacToe
A 3 by 3, two dimensional array for cells.
A label to display game status.
Run as Application
Run as Applet
Liang,Introduction to Java Programming,revised by Dai-kaiyu
29
Optional
Case Study: Bouncing Ball
Objective: Write an
applet that displays a ball
bouncing in a panel. Use
two buttons to suspend
and resume the
movement and use a
scroll bar to control the
bouncing speed.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
30
Case Study: Bouncing Ball, cont.
JPanel
JPanel ActionListener AdjustmentListener
-char token
1
+getToken
Ball
+setToken
+paintComponet
-x: int
+mouseClicked
-y: int
-dx: int
-dy: int
-radius: int
-delay: int
-timer: Timer
+Ball()
+run(): void
+suspend(): void
+resume(): void
+setDelay(delay: int): void
Ball
-char
token
1
-char token
BallControl
1
1
+getToken
+setToken
-ball: Ball
+paintCo
-jsbDelay: int
mponet
-jbtResume: JButton
+mouseCli
-jbtSuspend: JButton
cked
+BallControl()
+actionPerformed(e: ActionEvent): void
+adjustmentValueChanged
(AdjustmentEvent e): void
BallControl
JApplet
BounceBallApp
Liang,Introduction to Java Programming,revised by Dai-kaiyu
+getToken
BounceBallApp
+setToken
+paintComponet
+BounceBallApplet()
+mouseClicked
+main(args:
String[]): void
Run
31
Optional
What is Multimedia?
Multimedia is a broad term that encompasses making, storing,
retrieving, transferring, and presenting various types of information,
such as text, graphics, pictures, videos, and sound.
 Multimedia involves a complex weave of communications,
electronics, and computer technologies. It is beyond the scope of this
book to cover multimedia in great detail. This chapter concentrates
on the presentation of multimedia in Java.
Whereas most programming languages have no built-in multimedia
capabilities, Java was designed with multimedia in mind. It provides
extensive built-in support that makes it easy to develop powerful
multimedia applications. Java's multimedia capabilities include
animation that uses drawings, audio, and images.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
32
Optional
The URL Class
Audio and images are stored in files. The java.net.URL class can be
used to identify the files on the Internet. In general, a URL (Uniform
Resource Locator) is a pointer to a "resource" on the World Wide
Web. A resource can be something as simple as a file or a directory.
You can create a URL object using the following constructor:
public URL(String spec) throws MalformedURLException
For example, the following statement creates a URL object for
http://www.sun.com:
try {
URL url = new URL("http://www.sun.com");
}
catch(MalformedURLException ex) {
}
Liang,Introduction to Java Programming,revised by Dai-kaiyu
33
Creating a URL for Local Files
The following statement creates a URL object for the file
c:\book\image\us.gif.
try {
URL url = new URL("c:\\book\\image\\us.gif");
}
catch(MalformedURLException ex) {
}
The preceding statement creates a URL for the absolute file name
c:\book\beep.au on the Windows. There are two problems: (1) the file
location is fixed; (2) it is platform-dependent. To circumvent these
problems, you can create the URLs for files using through the
resource of the class file using the java.lang.Class class.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
34
Creating a URL from a Class Reference
Whenever the Java Virtual Machine loads a class or an interface, it creates an
instance of a special class named Class. The Class class provides access to useful
information about the class, such as the data fields and methods. It also contains
the getResource(filename) method, which can be used to obtain the URL of a
given file name in the same directory with the class or in its subdirectory. As
discussed in Section 8.4.5, “The getClass Method,” you can obtain the class for the
object at runtime. Thus, you can use the following code to get the URL of a file:
Class class = this.getClass();
URL url = class.getResource(filename);
where filename is a relative file name in the same directory or a subdirectory of
the class. Suppose you run a class stored in c:\book, the following statement creates
a URL object for c:\book\image\us.gif.
URL url = this.getClass().getResource(“image/us.gif");
Liang,Introduction to Java Programming,revised by Dai-kaiyu
35
Creating ImageIcon Using Absolute File Names
You used the ImageIcon class to create an icon from an image file
and the setIcon method or the constructor to place the image in a
GUI component, such as a button and a label. For example, the
following statements create an ImageIcon and set it on an JLabel
object jlbl.
ImageIcon imageIcon = new ImageIcon("c:\\book\\image\\us.gif");
//ImageIcon imageIcon = new ImageIcon("image/us.gif");
jlbl.setIcon(imageIcon);
This approach suffers a problem. The file location is fixed since it
uses the absolute file path on Window. Thus, the program cannot
run on other platforms and cannot run as applet.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
36
Creating ImageIcon Using Class Reference
To circumvent this problem, you can create the URLs for
files through the class reference using the java.lang.Class
class. For example, suppose the class file is in c:\book, the
following statements create a URL for
c:\book\image\us.gif.
Class class = this.getClass();
URL url = class.getResource("image/us.gif");
You can now create an ImageIcon using
ImageIcon imageIcon = new ImageIcon(url);
Liang,Introduction to Java Programming,revised by Dai-kaiyu
37
Creating Image From ImageIcon
An image icon displays a fixed-size image. To display an
image in a flexible size, you need to use the
java.awt.Image class. An image can be created from an
image icon as follows:
Image image = imageIcon.getImage();
Given an Image, you can create an ImageIcon using
ImageIcon imageIcon = new ImageIcon(image);
Liang,Introduction to Java Programming,revised by Dai-kaiyu
38
Drawing Images in Graphics
Using a label as an area for displaying images is simple and convenient, but you
don't have much control over how the image is displayed. A more flexible way to
display images is to use the drawImage method of the Graphics class on a panel
using one of the foure overloaded drawImage method.
drawImage(Image img, int x, int y,
observer)
drawImage(Image img, int x, int y,
drawImage(Image img, int x, int y,
ImageObserver observer)
drawImage(Image img, int x, int y,
bgcolor, ImageObserver observer)
Color bgcolor, ImageObserver
ImageObserver observer)
int width, int height,
int width, int height, Color
ImageObserver is an asynchronous update interface that receives notifications of
image information as the image is constructed. The Component class implements
ImageObserver. Therefore, every GUI component is an instance of ImageObserver.
To draw images using the drawImage method in a Swing component, such as
JPanel, override the paintComponent method to tell the component how to display
the image in the panel.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
39
Displaying Image
Write a program that displays an image from
/image/us.gif in the class directory on a panel.
DisplayImage
Liang,Introduction to Java Programming,revised by Dai-kaiyu
Run
40
Case Study: ImageViewer Component
javax.swing.JPanel
ImageViewer
-image: Image
Image in the image viewer.
-imageFilename: String
Filename of the image.
-stretched: boolean
True if the image is stretched in the viewer.
-xCoordinate: int
x-Coordinate of the upper left corner of the image in the viewer.
-yCoordinate: int
y-Coordinate of the upper left corner of the image in the viewer.
+ImageViewer()
Constructs an image viewer with no image.
+ImageViewer(image: Image)
Constructs an image viewer with the specified image.
+createImage(imageFilename:
String, object: Object): Image
Creates an image from the specified image file.
+createImageIcon(imageFilename:
String, object: Object): ImageIcon
Creates an image icon from the specified image file.
+createImage(urlString: String):
Image
Creates an image from the specified URL string.
+createImageIcon(urlString:
String): ImageIcon
Creates an image icon from the specified URL string.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
ImageViewer 41
Six Flag Example
Objective: Use the
ImageViewer class
to display six flags.
SixFlags
Liang,Introduction to Java Programming,revised by Dai-kaiyu
Run
42
Case Study: Image Animation
 Objective: Simulate a movie by displaying a sequence
of images in a control loop.
ImageAnimation
Run as an Application
Liang,Introduction to Java Programming,revised by Dai-kaiyu
43
Creating AudioClip from an Audio File
To play an audio file in an applet, first create an audio clip object for
the audio file. The audio clip is created once and can be played
repeatedly without reloading the file. To create an audio clip, use the
static method newAudioClip() in the java.applet.Applet class:
AudioClip audioClip = Applet.newAudioClip(url);
Audio was originally used with Java applets. For this reason, the
AudioClip interface is in the java.applet package.
The following statements, for example, create an AudioClip for the
beep.au audio file in the same directory with the class you are running.
Class class = this.getClass();
URL url = class.getResource("beep.au");
AudioClip audioClip = Applet.newAudioClip(url);
Liang,Introduction to Java Programming,revised by Dai-kaiyu
44
Playing Audio
java.applet.AudioClip
+play()
Starts playing this audio clip. Each time this method is called, the clip is
restarted from the beginning.
+loop()
Plays the clip repeatedly.
+stop()
Stops playing the clip.
To manipulate a sound for an audio clip, use the play(), loop(), and
stop() methods in java.applet.AudioClip.
Liang,Introduction to Java Programming,revised by Dai-kaiyu
45
Playing Anthem Example
Objective: Display
images and playing
audio in applets
and in applications.
FlagAnthem
Run as an Application
Liang,Introduction to Java Programming,revised by Dai-kaiyu
46
Optional
Packaging and Deploying
Java Projects
What is JAR?
Java archive file can be used to group all the project files in a
compressed file for deployment.
The Java archive file format (JAR) is based on the popular ZIP file
format.
This single file can be deployed on an end-user’s machine as an
application. It also can be downloaded to a browser in a single HTTP
transaction, rather than opening a new connection for each piece. This
greatly simplifies application deployment and improves the speed
with which an applet can be loaded onto a web page and begin
functioning.
47
Liang,Introduction to Java Programming,revised by Dai-kaiyu
Creating JAR
You can use the JDK jar command to create an
archive file. The following command creates an
archive file named TicTacToe.jar for classes
TicTacToe.class and TicTacToe$Cell.class.
jar -cf TicTacToe.jar TicTacToe.class TicTacToe$Cell.class
The -c option is for creating a new archive file, and
the -f option specifies the archive file’s name.
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48
Viewing the Contents of a JAR File
You can view the contents of a .jar file using
WinZip.
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49
Manifest File
A manifest file was created with the path name meta-inf\. The
manifest is a special file that contains information about the files
packaged in a JAR file. For instance, the manifest file in
TicTacToe.jar contains the following information:
Manifest-Version: 1.0
Name: TicTacToe.class
Java-Bean: True
Name: TioTacToe$Cell.class
Java-Bean: True
You can modify the information contained in the manifest file to
enable the JAR file to be used for a variety of purposes. For instance,
you can add information to specify a main class to run an application
using the .jar file.
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50
Running Archived Projects Standalone
The manifest file must have an entry to contain the
main class. For example, to run TicTacToe, you
need to insert the following two lines in the manifest
file:
Main-Class: TicTacToe
Sealed: true
Run the .jar file using the java command from the
directory that contains TicTacToe.jar,
java -jar TicTacToe.jar
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51
Create file for double click to run
 Javac to compile the source file to .class file, for
example, TestUI.class
 Create a config file , name it , for example, conf.txt.
Put the following in it:
Main-Class: TestUI
Create-By: 1.5
 Make a runnable jar file from the following command:
jar cmf conf.txt TestUI.jar TestUI.class
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52
Running Archived Projects As Applet
To run TicTacToe as an applet, modify the <APPLET> tag
in the HTML file to include an ARCHIVE attribute. The
ARCHIVE attribute specifies the archive file in which the
applet is contained. For example, the HTML file for
running TicTacToe can be modified as shown below:
<APPLET
CODE = "TicTacToe.class"
ARCHIVE = "TicTacToe.jar"
WIDTH = 400
HEIGHT = 300
HSPACE = 0
VSPACE = 0
ALIGN = Middle
>
</APPLET> Liang,Introduction to Java Programming,revised by Dai-kaiyu
53
Optional
Pluggable Look-and-Feel
The pluggable look-and-feel feature lets you design
a single set of GUI components that automatically
has the look-and-feel of any OS platform. The
implementation of this feature is independent of the
underlying native GUI, yet it can imitate the native
behavior of the native GUI.
Currently, Java supports the following three lookand-feel styles:
·
·
·
Metal
Motif
Windows
Liang,Introduction to Java Programming,revised by Dai-kaiyu
54
Setting Look-And-Feel
The javax.swing.UIManager class manages the
look-and-feel of the user interface. You can use one
of the following three methods to set the look-andfeel for Metal, Motif, or Windows:
UIManager.setLookAndFeel
(UIManager.getCrossPlatformLookAndFeelClassName());
UIManager.setLookAndFeel
(new com.sun.java.swing.plaf.motif.MotifLookAndFeel());
UIManager.setLookAndFeel
(new
com.sun.java.swing.plaf.windows.WindowsLookAndFeel()
);
TestUI
Liang,Introduction to Java Programming,revised by Dai-kaiyu
55
Setting Look-And-Feel in Static Initialization
Block
To ensure that the setting takes effect, the
setLookAndFeel method should be executed before
any of the components are instantiated. Thus, you
can put the code in a static block, as shown below:
static {
try {
// Set a look-and-feel, e.g.,
//UIManager.setLookAndFeel
// (UIManager.getCrossPlatformLookAndFeelClassName());
}
catch (UnsupportedLookAndFeelException ex) {}
}
Liang,Introduction to Java Programming,revised by Dai-kaiyu
56