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
    • for Loops
    • while Loops
    • do-while Loops
    • Exiting a Loop
    • Naming a Loop
    • Workshop: Teaching Your Computer a Lesson
    • Summary
    • Q&A
    • Quiz
    • Activities
  • 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

while Loops

The while loop does not have as many different sections to set up as the for loop. The only thing it needs is a conditional test, which accompanies the while statement. The following is an example of a while loop:

while (gameLives > 0) { 
    // the statements inside the loop go here 
} 

This loop will continue repeating until the gameLives variable is no longer greater than 0.

The while statement tests the condition at the beginning of the loop, before any statements in the loop have been handled. For this reason, if the tested condition is false when a program reaches the while statement for the first time, the statements inside the loop will be ignored.

If the while condition is true, the loop goes around once and tests the while condition again. If the tested condition never changes inside the loop, the loop will keep looping indefinitely.

The following statements cause a while loop to display the same line of text several times:

int limit = 5; 
int count = 1; 
while (count < limit) { 
    System.out.println("Frodo lives!"); 
    count++; 
} 

A while loop uses one or more variables that are set up before the loop statement. In this example, two integer variables are created: limit, which has a value of 5, and count, which has a value of 1.

The while loop displays the text Frodo lives! four times. If you gave the count variable an initial value of 6 instead of 1, the text would never be displayed.

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