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Need help understanding jar file construction to utilize custom classHelpful Member! 

motoslide (MIS) (OP)
29 Mar 11 13:13
Newbie alert:
I have a vendor-supplied integration utility written in Java. They supplied a couple of jar files and a sample class which uses those custom methods. I now need to create my own jar file of a modified version of their example, and use that in a "java aware" application.
How do I create my custom jar file? Specifically, is the name of the jar file important, and the directory structure therein?
Should my jar file incorporate the vendor-supplied jar files, or do I need to move all 3 of them together as needed.
To help illustrate:
The sample code is called "SigCaptureDemo.class". I created a jar file called "BarSign.jar", which contains that class file and a MANIFEST.MF file. If I add "BarSign.jar" to my classpath, what would my corresponding "import" statement be?

I'd like to see an example of creating a custom "Hello World" class which can be used by another application and pass it a variable for the second word. In other words, allow it to print "Hello Earth", or "Hello AnyVariable". I think that would provide me with the understanding to address my specific needs.

Thanks for any pointers. Sorry that was such a long question.

"Proof that there is intelligent life in Oregon.  Well, Life anyway."

Helpful Member!  Diancecht (Programmer)
30 Mar 11 3:05
I'm not sure about how to start to answer your question. About jar files, you can pack them as you want, I don't think there's a fixed rule. A jar is like a container, a zip file intended to ease the burden of deliver a bunch of .class files, so you can do a single jar file with vendor and your classes.

Not sure if I'm helping, maybe this tutorial helps.


motoslide (MIS) (OP)
30 Mar 11 20:06
Thanks for the link to that tutorial. I've scanned quite a bit of it, but I still need a "push".

In one of their examples, I've created 3 small classes called Server, Client, and Utility. I've create a jar file which includes a "Main-Class:" label in the manifest file which allows the "Server" to be launched directly from a command line.

Now, I want to "include" those classes for another test project. I've added the jar file to my classpath. I've added "package myclass" at the beginning of each source file (then re-compiled and re-created the myclass.jar file). On my new project, I have this as my first line:
import myclass.*;
I get a compile-time error:
package myclass does not exit

Where am I going astray?

"Proof that there is intelligent life in Oregon.  Well, Life anyway."

Diancecht (Programmer)
31 Mar 11 5:25
Packages and imports have nothing to do with jars.

I'd take a look at the use of packages here before going on further.


motoslide (MIS) (OP)
6 Apr 11 20:46
Thanks once again.
I've been beating my head and have made some progress. I have a custom class now which does what I need and I'm able to launch it from within my "java aware" application. The utility runs as a frame with just a few buttons to capture a graphic and save it to a disk file. The only part which is still failing is my inability to close down the process. The demo I downloaded had a "System.exit(0)" line, which isn't allowed because my calling application is also running in the JVM. I changed that to a "dispose()". That appears to work, but my CPU pegs at 100% and stays there until I kill the JVM. Is there a better way to discard the frame once it has accomplished my needs?


"Proof that there is intelligent life in Oregon.  Well, Life anyway."

Diancecht (Programmer)
7 Apr 11 2:42
A call to setVisible(false) is also adviceable, and be sure there are no references to the JFrame so the garbage collection can get rid of it.


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