File APIs for Java Developers
Manipulate DOC, XLS, PPT, PDF and many others from your application.
The moose likes Beginning Java and the fly likes Jar Files and Classpath Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login

JavaRanch » Java Forums » Java » Beginning Java
Bookmark "Jar Files and Classpath" Watch "Jar Files and Classpath" New topic

Jar Files and Classpath

J Solomon
Ranch Hand

Joined: Oct 08, 2012
Posts: 30

I have a question and any help would be greatly appreciated. My question is regarding setting classpath and jar files. Say I have a typical 'HelloWorld.class' and it lives in '/home/me/' dir. I execute it as follows:

Now say I package that class up in a jar file, using a manifest file that points to HelloWorld as the entry point, do I need to give a classpath when I execute that jar file, or is the jar format aware of the classpath? I understand if I would like to reference other jar files then I would need to make sure the appropriate classpath is defined for each jar file in the manifest, but what about just that one class in simplest form?

I know this probably sounds confusing so please let me know if it needs further clarification.
Paul Clapham

Joined: Oct 14, 2005
Posts: 19528

No. In fact when you run an executable jar (via "java -jar executable.jar") you cannot specify a classpath at the command line. The classpath is entirely based on the jar file and nothing else (no -cp argument, no CLASSPATH environment variable, nothing else).

So if your executable jar contained only the HelloWorld class, you just run it using the "java -jar" command. If it happens that the HelloWorld class needs access to other classes which aren't in the jar, then the jar's manifest should have a "Class-Path" entry which says what those jars are and where they are relative to the executable jar.
I agree. Here's the link:
subject: Jar Files and Classpath