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
    • Choosing a Language
    • Telling the Computer What to Do
    • How Programs Work
    • How Programs Don't Work
    • Next Stop: Java
    • Workshop: Installing a Java Development Tool
    • Summary
    • Q&A
    • Quiz
    • Activities
  • 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
  • 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

How Programs Work

Most computer programs are written in the same way that you write a letter—by typing each statement into a word processor. Some programming tools come with their own word processor, and others can be used with any text-editing software. If you don't already have a tool that can be used for Java programming, you can use the free Java 2 Software Development Kit, which you will learn about later in this hour, with any of your favorite editors.

When you have finished writing a computer program, you save the file just like saving any other document to disk. Computer programs often have their own filename extension to indicate what type of file they are. Java programs have the extension .java; an example of a Java program file name is Calculator.java.

To run a program you have saved as a file, you need some help. The kind of help that's needed depends on the programming language you're using. Some languages require an interpreter to run their programs. The interpreter is a program that interprets each line of a computer program and tells the computer what to do. Most versions of BASIC are interpreted languages. The advantage of interpreted languages is that they are faster to test. When you are writing a BASIC program, you can try it out immediately, spot any errors, fix them, and try again. The primary disadvantage is that interpreted languages run more slowly than other programs.

Other programming languages require a compiler. The compiler takes a computer program and translates it into a form that the computer can understand. It also does what it can to make the program run as efficiently as possible. The compiled program can be run directly without the need for an interpreter. Compiled programs run more quickly than interpreted programs, but they take more time to test. You have to write your program and compile it before trying it out. If you find an error and fix it, you must compile the program again to verify that the error is gone.

Java is unusual because it requires a compiler and an interpreter. You'll learn more about this later as you write Java programs.

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