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

Receiving Parameters in the Applet

You have to do something in your Java program to retrieve the parameters on the Web page or they will be ignored. The getParameter() method of the JApplet class retrieves a parameter from a <PARAM> tag on a Web page. The parameter name, which is specified with the NAME attribute on the page, is used as an argument to getParameter(). The following is an example of getParameter() in action:

String display1 = getParameter("Headline1"); 

The getParameter() method returns all parameters as strings, so you have to convert them to other types as needed. If you want to use a parameter as an integer, you could use statements such as the following:

int speed; 
String speedParam = getParameter("SPEED"); 
if (speedParam != null) 
    speed = Integer.parseInt(speedParam); 

This example sets the speed variable by using the speedParam string. You have to test for null strings before setting speed because the parseInt() method cannot work with a null string. When you try to retrieve a parameter with getParameter() that was not included on a Web page with the <PARAM> tag, it will be sent as null, which is the value of an empty string.

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