Fundamentals - SCJP Sun Certified Programmer for Java Platform SE6 - page 16

FIGURE 1.3 The source code and bytecode are typically stored in separate folders.

• c:\myproject\
• +src\
• | +com\
• | +sybex\
• | +demos\
• | | +TestColors.java
• | +events\
• | +ColorChanger.java
• +build\
• +com\
• +sybex\
• +demos\
• | +TestColors.class
• +events\
• +ColorChanger.class

A typical exam question at this point is to ask what the CLASSPATH needs to be for you to
run the TestColors program at the command prompt from any working directory. Do you
know the answer? I will reveal it in a moment, but fi rst here is the command prompt that
runs the TestColors application if you execute it from the c:\myproject\build directory:

java com.sybex.demos.TestColors

Notice the fully qualifi ed class name of TestColors must be specifi ed to execute
properly. Using the fully qualifi ed name has nothing to do with CLASSPATH or the current
working directory. The following command does not work and results in a java.lang
.NoClassDefFoundError , no matter what directory you run it from or what your CLASSPATH
is set to :

java TestColors

Why will this never work? Because there is no class called TestColors . Remember,
putting a class in a package changes the name of the class. Because TestColors is in the
com.sybex.demos package, the name of the class is com.sybex.demos.TestColors , and that
name must be used on the command line.
By the way, the answer to the question earlier about CLASSPATH is it needs to contain
c:\myproject\build :

set CLASSPATH=c:\myproject\build;

With this CLASSPATH , the command to run the TestColors program can be executed
from any directory.