L06 (Chapter 16) Applets and Multimedia 2

1Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-222158-6

L06 (Chapter 16) Applets and Multimedia 2

Chapter 12 GUI Basics

Chapter 14 Event-Driven Programming

Chapter 15 Creating User Interfaces

§10.2, “Abstract Classes,” in Chapter 10

Chapter 13 Graphics

Chapter 16 Applets and Multimedia

§10.4, “Interfaces,” in Chapter 10


Case Study: TicTacToe

Cell

-token: char

+getToken():char

+setToken(token: char): void

#paintComponent(g: Graphics): void

+mouseClicked(e: MouseEvent): void

JPanel -char token +getToken +setToken +paintComponet +mouseClicked

Token used in the cell (default: ' ').

Returns the token in the cell.

Sets a new token in the cell.

Paints the token in the cell.

Handles a mouse click on the cell.

Optional


Case Study: TicTacToe, cont.

Run as AppletRun as AppletTicTacToeTicTacToe Run as ApplicationRun as Application

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9

TicTacToe

-whoseTurn: char

-cell: Cell[][]

-jlblStatus: JLabel

+TicTacToe()

+isFull(): boolean

+isWon(token: char): boolean

JApplet -char token +getToken +setToken +paintComponet +mouseClicked

Cell -char token +getToken +setToken +paintComponet +mouseClicked

Indicates which player has the turn, initially 'X'.

A 3 by 3, two dimensional array for cells.

A label to display game status.

Constructs the TicTacToe user interface.

Returns true if all cells are filled.

Returns true if a player with the specified token has won.


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.

OptionalCase Study: Bouncing Ball


Case Study: Bouncing Ball, cont.

BallBall BallControlBallControl BounceBallAppBounceBallApp RunRun

BounceBallApp +BounceBallApp() +main(args: String[]): void

JApplet -char token +getToken +setToken +paintComponet +mouseClicked

BallControl -ball: Ball -jsbDelay: JScrollBar -jbtResume: JButton -jbtSuspend: JButton +BallControl()


Ball -x: int -y: int -dx: int -dy: int -radius: int -delay: int -timer: Timer +Ball() +suspend(): void +resume(): void +setDelay(delay: int): void


1 1 1 1


Locating Resource from Applets

Due to security restrictions, applets cannot access local files. How can an applet load resource files for image and audio?


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");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.

Creating ImageIcon Using Absolute File Names


Assume that image/us.gif is under the class directory, you can circumvent this problem by using a relative path as follows:

ImageIcon imageIcon = new ImageIcon("image/us.gif");jlbl.setIcon(imageIcon);

This works fine with Java applications on all platforms, but does not work with Java applets because applets cannot load local files. To make it to work with both applications and applets, you need to locate the file using the URL class.

Creating ImageIcon Using Relative File Names


Locating Resource Using the URL Class The java.net.URL class can be used to identify files (image, audio, text, etc.) on the Internet. In general, a URL (Uniform Resource Locator) is a pointer to a “resource” on the World Wide Web on a local machine or a remote host. A resource can be something as simple as a file or a directory.

An URL for a file can also be accessed by class code in a way that is independent of the location of the file as long as the file is located in the class directory. Recall that the class directory is where the class (i.e., the .class file) is stored. For example, all the classes in this book are stored in c:\book. So the class directory is c:\book.


Creating a URL from a Class ReferenceAs discussed in §9.11.5, “The getClass Method,” when a class is loaded, the JVM creates a meta-object for the class, which can be obtained using

java.lang.Class metaObject = this.getClass();

The Class class provides access to useful information about the class, such as the data fields, constructors, and methods. It also contains the getResource(filename) method, which can be used to obtain the URL of a given file name in the class directory.

To obtain the URL of a file in the class directory, use

URL url = metaObject.getResource(filename);

For example, suppose the class directory is c:\book, the following statements create a URL for c:\book\image\us.gif.

Class metaObject = this.getClass();URL url = metaObject.getResource("image/us.gif");

You can now create an ImageIcon using

ImageIcon imageIcon = new ImageIcon(url);


Displaying Image

Write a program that displays an image from /image/us.gif in the class directory on a panel.

DisplayImageWithURLDisplayImageWithURL RunRun


Creating AudioClip from an Audio FileTo 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);


Playing Audio

To manipulate a sound for an audio clip, use the play(), loop(), and stop() methods in java.applet.AudioClip.

DisplayImagePlayAudioDisplayImagePlayAudio RunRun

«interface»

java.applet.AudioClip

+play()

+loop()

+stop()

Starts playing this audio clip. Each time this method is called, the clip is restarted from the beginning.

Plays the clip repeatedly.

Stops playing the clip.


Multimedia Animation

ImageAudioAnimationImageAudioAnimation Run as an ApplicationRun as an Application


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.

Optional


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.

Optional


Viewing the Contents of a JAR FileYou can view the contents of a .jar file using

WinZip.

Optional


Manifest FileA 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.classJava-Bean: True Name: TioTacToe$Cell.classJava-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.

Optional


Running Archived Projects StandaloneThe 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: TicTacToeSealed: true

Run the .jar file using the java command from the directory that contains TicTacToe.jar,

java -jar TicTacToe.jar

TIP: You can write an installation procedure that creates the necessary directories and subdirectories on the end-user’s computer. The installation can also create an icon that the end-user can double-click on to start the program. For information on creating Windows desktop icon, please see www.prenhall.com/liang/intro5e.html.

Optional


Running Archived Projects As AppletTo 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>

Optional


Pluggable Look-and-FeelThe 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 look-and-feel styles: · Metal · Motif · Windows

Optional


Setting Look-And-FeelThe 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-and-feel 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());

Optional


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) {} }

Static initialization blocks are executed when the class is loaded. For more information on static initialization blocks, please refer to Section 8.12, “Initialization Block.”

Optional

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L06 (Chapter 16) Applets and Multimedia 2