Working with classpaths in Java isn't too hard, but there are some rules
to follow.
1. Simplest scenario: Executing in the same directory, and there are no
package definitions in your source code. Example: HelloWorld, no package
definition. Execute from that directory, no classpath definition needed.
eg.
Class HelloWorld { ... }
2. Next simplest: You compile without packages defined:
using the same directory for source and compiled classes, or if you
compiled classes to a different directory:
export CLASSPATH=<pathtoyourclasslocation>
example directory: /opt/myapp/lib/
then
export CLASSPATH=/opt/myapp/lib/
and call it:
java HelloWorld
3. Adding a package definition to your source code, and there is a
definite source code hierachy. Using the package example below:
package project.testjava;
Class HelloWorld { ... }
Your directory structure should look like this:
<pathtoyoursourcelocation>/project/testjava/HelloWorld.java
Assuming that you compile your code in the same directory and deposit the
class files there, then set your classpath as follows:
export CLASSPATH=<pathtoyoursourcelocation>
e.g. Using /opt/myapp/source/ as <pathtoyoursourcelocation>:
ex. export CLASSPATH=/opt/myapp/source/
and call the application as follows:
java project.testjava.HelloWorld
--------------------------------------------
If you compile to a different location, then your directory structure will
look like this after a compilation:
<pathtoyoursourcelocation>/project/testjava/HelloWorld.java
<pathtoyourclasslocation>/project/testjava/HelloWorld.class
Then set the classpath as follows:
export CLASSPATH=<pathtoyourclasslocation>
e.g. Using /opt/myapp/lib as <pathtoyourclasslocation>
export CLASSPATH=/opt/myapp/lib
and call the application as follows:
java project.testjava.HelloWorld
3. You've compiled to a jarfile, e.g. MyHelloWorld.jar
export CLASSPATH=<pathtojar>/MyHelloWorld.jar
e.g. Using /opt/myapp/lib as <pathtoyourclasslocation>
export CLASSPATH=/opt/myapp/lib
and call as follows:
java project.testjava.HelloWorld
-Bob
> On Saturday 29 May 2004 05:44 pm, you wrote:
>> That didn't work. I still get the NoClassDefFoundError. Any other
>> ideas?
>
> You're right !! it doesn't work. I just try this myself, and whenever I
> try to
> execute from outside the directory where the java files is located, I got
> the
> same error. I thought I've seen this and what I suggested was the
> solution,
> obviously not ! (Now it should be obvious that I am not a java developer
> myself, I just play with it sometime)
>
> After some searching myself, I only have this solution:
>
> If for example, my java program is in ~/project/testjava/helloworld.java,
> I
> can put in helloworld.java:
>
> package project.testjava;
> <rest of the src code>
>
> then I need to go to ~, and compile it from there:
> javac project/testjava/helloworld.java
>
> and running it from there would work tpp:
> java project/testjava/helloworld
>
> The problems with the solution: First, I can't find a way so that I can
> use
> absolute path during compile and running (which is probably what you want
> in
> your case, since you're going to put the command in rc.local). So what I
> want
> is something so that I can say:
>
> javac /home/<username>/project/testjava/helloworld.java
> java /home/<username>/project/testjava/helloworld
>
> when I tried, the solution does not work. I can't also figure out what to
> put
> in after the "package" keyword in the source code to make the absolute
> path
> work.
>
> Secondly, the source code is dependent on what directory you want to
> compile
> and run the java program from. Unless I am missing something, that is just
> plain stupid !! Source code of a program should never be dependent on
> where
> the program is running from.
>
> So that's it. I am kinda stuck right now too. I don't know if that would
> help
> you, but if you find the real solution, please let me know, cause right
> now
> it bugs the hell out of me too ! (BTW, I have a task of writing some java
> program in the near future, so this would be good to know).
>
> I know this is going OT, but if anyone else on the list know a solution,
> please help.
>
> RDB
>
>
>> On Sat, 2004-05-29 at 11:59, Reuben D. Budiardja wrote:
>> > On Saturday 29 May 2004 12:16 pm, Michael Sullivan wrote:
> <snip>I wrote a java server that I want to start every time
>> > > my server PC restarts. I created a /usr/local/classes directory and
>> > > copied Server.class and the support classes it uses there. Id cd'd
>> to
>> > > /usr/local/classes and issued a java Server from there and it works
>> > > fine, but if I issue a java /usr/local/classes/Server from anywhere
>> > > outside the /usr/local/classes directory it tells me
>> > >
>> > > Exception in thread "main" java.lang.NoClassDefFoundError:
>> > > /usr/local/classes/Server
> <snip>
>> > Try the following:
>> > set the environment variable CLASSPATH to /usr/local/classes so that
>> Java
>> > knows where to find your classes. Asumming you're using bash:
>> > $> export CLASSPATH=$CLASSPATH:/usr/local/classes
>> >
>
>
> --
> Reuben D. Budiardja
> Department of Physics and Astronomy
> The University of Tennessee, Knoxville, TN
> ---------------------------------------------------------
> "To be a nemesis, you have to actively try to destroy
> something, don't you? Really, I'm not out to destroy
> Microsoft. That will just be a completely unintentional
> side effect."
> - Linus Torvalds -
>
>
> --
> redhat-list mailing list
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