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
  • 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
    • Standard Applet Methods
    • Putting an Applet on a Web Page
    • A Sample Applet
    • The Java Plug-in
    • Sending Parameters from a Web Page
    • Receiving Parameters in the Applet
    • Workshop: Handling Parameters in an Applet
    • Summary
    • Q&A
    • Quiz
    • Activities
  • 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

Sending Parameters from a Web Page

Now that you have had some experience writing computer programs, you might be feeling one of the strongest emotions of the programmer: compiler angst. Even though it takes no more than 15 seconds to compile most programs, that time can seem interminable when you're debugging a program. Write, save, compile, Aargh—an error! Write, save, compile, Aargh! Write, save, compile, Aargh!… As this vicious cycle repeats itself, it's easy to become world-weary as a program is compiled and recompiled.

One of the driving forces behind parameter use in Java applets is the fear and loathing of compilation. Parameters enable you to change elements of an applet without editing or recompiling anything. They also make the program more useful.

Parameters are stored as part of the Web page that contains an applet. They are created using the HTML tag <PARAM> and its two attributes: NAME and VALUE. You can have more than one <PARAM> tag with an applet, but all of them must be between the opening <APPLET> tag and the closing </APPLET> tag (or the <OBJECT> and </OBJECT> tags, which also support parameters). The following is an <APPLET> tag that includes several parameters:

<APPLET CODE="ScrollingHeadline.class" HEIGHT=50 WIDTH=400> 
<PARAM NAME="Headline1" VALUE="Dewey defeats Truman"> 
<PARAM NAME="Headline2" VALUE="Stix nix hix pix"> 
<PARAM NAME="Headline3" VALUE="Man bites dog"> 
</APPLET> 

This example could be used to send news headlines to an applet that scrolls them across the screen. Because news changes all the time, the only way to create a program of this kind is with parameters. No other solution would work; just imagine how long it would take to recompile a Java program every time a National Basketball Association star player ran afoul of the law.

You use the NAME attribute to give the parameter a name. This attribute is comparable to giving a variable a name. The VALUE attribute gives the named parameter a value.

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