Background

Have you ever heard that unforgettable children's song 100 bottles of pop on the wall? Your task is to write a program that will "sing" a few verses of this song. Here's an example recording on Youtube, but beware it may get stuck in your head the rest of the day!

Objectives

• Step through code using a debuggger.

• Trace execution flow with a debuggger.

Part 1: Bottles of Pop

Download Bottles.java as a starting point for the lab. Write your name and today's date in the Javadoc comment. Here is what the output should look like when you finish the lab:

100 bottles of pop on the wall 100 bottles of pop If one of those bottles should happen to fall 99 bottles of pop on the wall 99 bottles of pop on the wall 99 bottles of pop If one of those bottles should happen to fall 98 bottles of pop on the wall (repeat until 1)

1. Most of the algorithm has already been implemented in Bottles.java. Figure out how to complete the sing method.

2. Test your solution on a small number of verses. You may want to run this lab from the command line (i.e., java Bottles 5) for convenience.

   • Is it working right? If not, go back and fix it!
   • Do you have a blank line after each verse?

3. Modify your code to print "1 bottle" instead of "1 bottles" when applicable.

   • Don't forget the ending of the "2 bottles of pop" verse.

4. Modify your code to print "No more bottles" instead of "0 bottles" when applicable.

5. Make sure your solution works in the following cases. Test each one via the command line.

   • java Bottles 0   nothing should print
   • java Bottles 1   the last verse prints
   • java Bottles 5   only five verses print

Part 2: Debugging with DrJava

Most integrated development environments (like DrJava, Eclipse, and NetBeans) come with a debugger that allows you to "step through" your code while it is running.

6. Move your cursor to the following line of code in DrJava:

   if (args.length > 0) {

7. Click the Debugger menu and select Toggle Breakpoint on Current Line (or just press Ctrl+B).

8. Click the Debugger menu again and select Debug Mode (or Ctrl+Shift+D).

9. Now click the Run button on the toolbar (or press F2). Your program should stop on the if statement.

10. At this point, you can take any of the following steps from the Debugger menu (or use the keyboard shortcuts):

    • Step Into (F12) -- run the current line of code (the default action)
    • Step Over (F11) -- run the current line, but don't step into other methods
    • Step Out (Shift-F12) -- run all code until it returns from the current method
    • Resume (F7) -- run all code until it reaches another breakpoint (if any)

11. Practice stepping through your code one line at a time. Each time the program ends, you will need to restart the debugger.

12. DrJava has an "Automatic Trace" feature that animates the entire execution of a program. Can you figure out how it works?

Submit your completed Bottles.java file via Canvas by the end of the day.