Sams Teach Yourself Java 2 in 24 Hours

By Rogers Cadenhead

• Table of Contents
  • Copyright
  • About the Author
  • About the Technical Editor
  • Acknowledgments
  • We Want to Hear from You!
  • Reader Services
  • Introduction
  • Hour 1. Becoming a Programmer
  • Hour 2. Writing Your First Program
  • Hour 3. Vacationing in Java
  • Hour 4. Understanding How Java Programs Work
    • Creating an Application
    • Sending Arguments to Applications
    • Applet Basics
    • Sending Parameters to Applets
    • Workshop: Viewing the Code Used to Run Applets
    • Summary
    • Q&A
    • Quiz
    • Activities
  • Part II: Learning the Basics of Programming
  • Hour 5. Storing and Changing Information in a Program
  • Hour 6. Using Strings to Communicate
  • Hour 7. Using Conditional Tests to Make Decisions
  • Hour 8. Repeating an Action with Loops
  • Part III: Working with Information in New Ways
  • Hour 9. Storing Information with Arrays
  • Hour 10. Creating Your First Object
  • Hour 11. Describing What Your Object Is Like
  • Hour 12. Making the Most of Existing Objects
  • Part IV: Programming a Graphical User Interface
  • Hour 13. Building a Simple User Interface
  • Hour 14. Laying Out a User Interface
  • Hour 15. Responding to User Input
  • Hour 16. Building a Complex User Interface
  • Part V: Creating Multimedia Programs
  • Hour 17. Creating Interactive Web Programs
  • Hour 18. Handling Errors in a Program
  • Hour 19. Creating a Threaded Program
  • Hour 20. Reading and Writing Files
  • Part VI: Creating Multimedia Programs
  • Hour 21. Using Fonts and Color
  • Hour 22. Playing Sound Files
  • Hour 23. Working with Graphics
  • Hour 24. Creating Animation
  • Part VII: Appendixes
  • Appendix A. Tackling New Features of Java 2 Version 1.4
  • Appendix B. Using the Java 2 Software Development Kit
  • Appendix C. Programming with the Java 2 Software Development Kit
  • Appendix D. Using Sun ONE Studio
  • Appendix E. Where to Go from Here: Java Resources
  • Appendix F. This Book's Web Site

Q&A

1. Can a single Java program be both an applet and an application?

   It is possible to make a program serve as both applet and application, but it's often an unwieldy solution unless the program is simple. An applet could be set up to run as an application also by including a main() block in the applet, but you would not be able to use the init() block or paint() block in the automatic fashion they are used in an applet. Most programs are written as either an application or as an applet, rather than attempting to do both.

2. Do all arguments sent to a Java application have to be strings?

   Java makes all arguments into strings for storage when an application runs. When you want to use one of these arguments as an integer or some other non-string type, you have to convert the value. You'll learn how to do this during Hour 11, "Describing What Your Object Is Like."

3. I get errors when I try to load RootApplet.html into either Mozilla or Microsoft Internet Explorer. What's the problem?

   In most cases, the problem is that the browser isn't equipped to run Java 2 applets. Internet Explorer and Netscape Navigator have built-in support for Java 1.0, the first widely available version of the language, and partial support for Java 1.1. Sun offers a Java Plug-in that makes it possible for both leading browsers to support Java 2 applets, but it only works if the Web page containing the applet is equipped to work with the plug-in. When you're in doubt about why an applet won't work in a browser, try loading it with the appletviewer tool included with the Software Development Kit. If it works in appletviewer, the problem is with the browser rather than your Java applet.

4. Why don't Java applets require the same kind of special access as gateway programs?

   Java applets don't have the same access requirements because they don't pose the same risk to a Web hosting provider. Gateway programs don't have much security in place to prevent the program from attempting to do harmful things to the machine presenting the Web page. Java applets, on the other hand, have strict restrictions to prevent them from being used to write harmful programs. Also, Java programs do not run on the Web site's machine—they run on the system of the person viewing the page. This means that the Web site's machine will not slow down due to numerous people running a Java applet on a page.

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