1. 1 Chapter 14 Applets, Images, and Audio

2. 2 Objectives F To explain how the Web browser controls and executes applets (§ 14.2). F To describe the init, start, stop, and destroy methods in the Applet class (§ 14.2). F To know how to embed applets in Web pages (§ 14.4). F To run applets from appletviewer and from Web browsers (§ 14.4). F To pass string values to applets from HTML (§ 14.5). F To write a Java program that can run as both an application and an applet (§ 14.6). F To get image files using the URL class and display images in the panel (§ 14.9 Optional). F To develop a reusable component ImageViewer to display images (§ 14.10 Optional). F To get audio files and play sound (§ 14.12 Optional). F To package and deploy Java projects using Java archive files (§ 14.13 Optional). F To use Swing pluggable look-and-feel (§ 14.14 Optional).

3. 3 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() {... } /** Other methods if necessary... */ }

4. 4 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.

5. 5 Browser Calling Applet Methods

6. 6 The init() Method Invoked when the applet is first loaded and again if the applet is reloaded. Common functions implemented in this method include creating threads, loading images, setting up user-interface components, and getting parameters from the tag in the HTML page.

7. 7 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). Functionality might include restarting threads (for example, to resume an animation) or simply telling the applet to run again.

8. 8 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. When the user leaves the page, any threads the applet has started—but not completed—will continue to run.

9. 9 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. Usually, you will not need to override this method unless you need to release specific resources, such as threads that the applet created.

10. 10 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. LoanAppletRun Applet Viewer

11. 11 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. F Add your own methods and data if necessary. F Applets are always embedded in an HTML page.

12. 12 The 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] >

13. 13 Running Applets in Java Plug-In (optional, not needed for IE 6 & Netscape 8) Why to Use Java Plug-In? Java Plug-in enables Web browsers to run Java applets consistently on all the platforms.

14. 14 How to Use Java Plug-In (optional not needed for IE 6 & Netscape 8) F Convert the HTML file to a new HTML file using the HTMLConverter Utility. The new HTML file contains the tags for invoking the Java Plug-In. F If the Plug-In is not installed, the new HTML file automatically downloads it from the Sun JavaSoft Web site.

15. 15 Passing Parameters to Applets <applet code = "DisplayMessage.class" width = 200 height = 50> alt="You must have a Java-enabled browser to view the applet"

16. 16 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. Run Applet ViewerDisplayMessage

17. 17 Applications vs. Applets F 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. F 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.

18. 18 Security Restrictions on Applets F Applets are not allowed to read from, or write to, the file system of the computer viewing the applets. F 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.

19. 19 Conversions Between Applications and Applets F Conversions between applications and applets are simple and easy. F You can always convert an applet into an application. F You can convert an application to an applet as long as security restrictions are not violated.

20. 20 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. Run as ApplicationRun as Applet DisplayMessageApp

21. 21 Case Study: TicTacToe Optional

22. 22 Case Study: TicTacToe, cont. Run as Applet TicTacToeRun as Application

23. 23 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. Optional Case Study: Bouncing Ball

24. 24 Case Study: Bouncing Ball, cont. BallBallControlBounceBallAppRun

25. 25 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. Optional

26. 26 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) { } Optional

27. 27 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.

28. 28 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");

29. 29 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

30. 30 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); Creating ImageIcon Using Class Reference

31. 31 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); Creating Image From ImageIcon

32. 32 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. Drawing Images in Graphics drawImage(Image img, int x, int y, Color bgcolor, ImageObserver observer) drawImage(Image img, int x, int y, ImageObserver observer) drawImage(Image img, int x, int y, int width, int height, Color bgcolor, ImageObserver observer) 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.

33. 33 Displaying Image Write a program that displays an image from /image/us.gif in the class directory on a panel. DisplayImage Run

34. 34 Case Study: ImageViewer Component ImageViewer

35. 35 Six Flag Example Objective: Use the ImageViewer class to display six flags. SixFlags Run

36. 36 Case Study: Image Animation F Objective: Simulate a movie by displaying a sequence of images in a control loop. ImageAnimationRun as an Application

37. 37 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);

38. 38 Playing Audio To manipulate a sound for an audio clip, use the play(), loop(), and stop() methods in java.applet.AudioClip.

39. 39 Playing Anthem Example Objective: Display images and playing audio in applets and in applications. FlagAnthem Run as an Application

40. 40 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

41. 41 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.

42. 42 Viewing the Contents of a JAR File You can view the contents of a.jar file using WinZip.

43. 43 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.

44. 44 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 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.

45. 45 Running Archived Projects As Applet To run TicTacToe as an applet, modify the 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 >

46. 46 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 look-and-feel styles: · Metal · Motif · Windows Optional

47. 47 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-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());

48. 48 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.”