Is there a way I can allow someone to run my Java program without them seeing the code?

Question

So basically I made a terminal-dependent Java program and want to start handing it out, but I can't seem to find a way to do that without giving them my code. When making a .jar file it only works on Windows.

When trying to run on Linux (CentOS) I get

  Exception in thread "main" java.lang.UnsupportedClassVersionError:

and

   Could not find the main class: MyClass. Program will exit.

I'm using the command java -jar MyJar.jar to run them on both. I am using JavaMail in this program so perhaps that could be an issue. There is only one class and it has a main in it.

If anyone even has any alternatives to using a jar file to deliver the program where the user can't read the code that'd be great too. Thanks!

`java.lang.UnsupportedClassVersionError` is thrown when your compile a class with a newer JDK than the one being used to run it. Make sure you're using the same version of Java on your linux machine and your windows machine. — Jeffrey, Jul 03 '13 at 19:30

score 3 · Accepted Answer · answered Jul 03 '13 at 19:30

The JDK that you've actually used to compile and build your Jar is more recent than compared to the one installed on your client's Linux machine. That's when JVM throws an

Exception in thread "main" java.lang.UnsupportedClassVersionError:

Ask your client to report his Java version by running the following on console

java -version

Then if you're using Eclipse set the target runtime of your project accordingly. If you're compiling your Java source files on your own use

javac -target 1.4 source/MyClass.java

Oh shoot, they were different versions! Thanks! I was using BlueJ on Windows to create the jar file — Big Money, Jul 03 '13 at 19:33

score 0 · Answer 2 · edited May 23 '17 at 11:50

To me it sounds like the problem is that you compiled the code on an incompatible version that you're running the code on. For example, you compiled it with JDK 1.7 but the CentOS OS has only the java 1.5 version installed. Here is some more detailed information on the matter.

As for the title of your question, no, you don't have to give them the java source for them to run it. So something else is going wrong. Most likely the answer I gave.

score 0 · Answer 3 · answered Jul 03 '13 at 19:32

Regarding question title:

Obfuscate your code. Dont print your name directly, use a generator method.

http://en.wikipedia.org/wiki/Obfuscation_(software)

http://www.yworks.com/en/products_yguard_about.htm

http://www.allatori.com/

http://www.zelix.com/

http://www.sable.mcgill.ca/JBCO/

score 0 · Answer 4 · answered Jul 03 '13 at 21:03

In addition to the version issue others have described, and the fact that you don't need to distribute the .java files, you'll need to set up a Class-Path entry in the manifest file of your application jar file to reference the JavaMail jar file, and you'll have to deliver your application jar file and the JavaMail jar file to users. That can be tricky to get right. You might want to look at One-JAR to solve that problem.

Is there a way I can allow someone to run my Java program without them seeing the code?

4 Answers4