Question

I have a client/server program that attempts to send and receive an object.

There are three packages: server, client and shared
shared contains only the Message class

I put Message.java from shared package into the same folder as calcclient package source files and calcserver package source files.

I compile using the line: javac -classpath .; (long list of client or server.java files) Message.java
They can compile.
Then I change directory up one level and ran with: java -classpath .; .Main

When I use Netbeans to run, the entire program works as per normal. But not if I run from command line. If its executed through command line, the program will work until it needs to use the Message object. Then it will show a NoClassDefFoundError

Am I putting the right files at the right places? How do I get the program to find shared package through command line?

Answer 1

The files are not in the right place. The Message class belongs to a different package so it shouldn’t be living with the other classes. From http://java.sun.com/j2se/1.5.0/docs/tooldocs/findingclasses.html :

User classes are classes which build
on the Java platform. To find user
classes, the launcher refers to the
user class path — a list of
directories, JAR archives, and ZIP
archives which contain class files.

A class file has a subpath name that
reflects the class’s fully-qualified
name. For example, if the class
com.mypackage.MyClass is stored under
/myclasses, then /myclasses must be in
the user class path and the full path
to the class file must be
/myclasses/com/mypackage/MyClass.class.
If the class is stored in an archive
named myclasses.jar, then
myclasses.jar must be in the user
class path, and the class file must be
stored in the archive as
com/mypackage/MyClass.class.

You have a couple of options:

The best solution is to take the time to learn Ant. Netbeans projects are built with Ant, which is a really great feature of Netbeans in my book, and you can open up the build.xml in your project and find a reasonably well commented description of what Netbeans does to build your project. And really I don’t think there would be many places around that run builds from the command line so learning something like Ant would be a great help.

The next level down in sophistication would be to manually build a Jar for your shared package and put it somewhere on the classpath.

The most basic approach is just to compile the java files into class files and put them in the appropriate directory reflecting the package name as explained in the quote above.