Can I run from command line program created by Eclipse?

Question

Using Eclipse I have created a SWT Hello World program. I was able to run this program from Eclipse and it worked fine.

In the "/home/myname/workspace/HelloWorldSWT" I found two files: HelloWorldSWT.java and HelloWorldSWT.class. I wanted to execute the corresponding program from the command line. First I tried to type "java HelloWorld" and I got the following error message:

Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld
   at gnu.java.lang.MainThread.run(libgcj.so.90)
Caused by: java.lang.ClassNotFoundException: HelloWorld not found in gnu.gcj.runtime.SystemClassLoader{urls=[file:./], parent=gnu.gcj.runtime.ExtensionClassLoader{urls=[], parent=null}}
   at java.net.URLClassLoader.findClass(libgcj.so.90)
   at gnu.gcj.runtime.SystemClassLoader.findClass(libgcj.so.90)
   at java.lang.ClassLoader.loadClass(libgcj.so.90)
   at java.lang.ClassLoader.loadClass(libgcj.so.90)
   at gnu.java.lang.MainThread.run(libgcj.so.90)

I also tried this "java -cp /home/roman/workspace/ HelloWorld.HelloWorld". As the result I got the following error message:

Exception in thread "main" java.lang.NoClassDefFoundError: loaded class HelloWorld.HelloWorld was in fact named HelloWorld
   at java.lang.VMClassLoader.defineClass(libgcj.so.90)
   at java.lang.ClassLoader.defineClass(libgcj.so.90)
   at java.security.SecureClassLoader.defineClass(libgcj.so.90)
   at java.net.URLClassLoader.findClass(libgcj.so.90)
   at gnu.gcj.runtime.SystemClassLoader.findClass(libgcj.so.90)
   at java.lang.ClassLoader.loadClass(libgcj.so.90)
   at java.lang.ClassLoader.loadClass(libgcj.so.90)
   at gnu.java.lang.MainThread.run(libgcj.so.90)

Does anybody know what I am doing wrong? Thank you in advance for any help.

Answer 1

It is possible that you are not loading the SWT library correctly, and as a result your class fails to load.

The SWT library is part of jars that are already loaded when you run Eclipse but are not loaded in a command line parameter. Did you modify your class path accordingly?

Here is an old article about how to do this sort of stuff in older versions of Eclipse http://www.ibm.com/developerworks/opensource/library/os-ecgui1/ You will need different jars today with latest version fo Eclipse. It might even come down to a single jar.

Check out the SWT FAQ; at least for Mac Carbon, you can use a single jar, I would bet you can do that for other platforms.

Also, I'm not 100% sure that you can run Eclipse under openJDK, which seems to be the case on your platform.

Answer 2

This is the problem which is caused because the JVM is not able to find the HelloWorld class as you have the class name as HelloWorldSWT with main method in it. try with

java HelloWorldSWT

Answer 3

Go to the Debug perspective, and select the program you just run (where it says Termintated, exit value...) Right click, and choose Properties, there you can see the whole command line command that was launched by eclipse.

You can run this same command in the same dir eclipse did (see in Run Configurations, Arguments, Working directory) and it will work.

Answer 4

You must add the directory where eclipse is storing the HelloWorldSWT.class file in the classpath. It is defined when the project is created, like "bin", "build" or "classes". Check the project properties or search the HelloWorldSWT.class file.

Assuming it is the build directory inside the HelloWorldSWT workspace and that your class is in no package (default package), the command should be:

java -cp /home/roman/workspace/HelloWorldSWT/build HelloWorldSWT

or just change to that directory and use:

java -cp . HelloWorldSWT

EDIT:
The -cp . means that only the actual directory is used for finding the class files. You must also add all libraries (JARs or other directories) used by your program (databse, SWT, ...).
For more details you can have a look at the documentation: How Classes are Found, Setting the Classpath and java comand

Answer 5

You have not set classpath correctly then.

I think it is usually more convenient to have the IDE build a jar-file with all non-jre libs included and execute that from the command-line.

java -jar myprogram.jar

What is the use of the program written in Eclipse if it can be easily executed only within the Eclipse?

That's really a good question, and deployment of java applications is really an art in itself. Both compilation and execution is - if not complicated - at least cumbersome when performed by hand. But Eclipse and other tools like Netbeans can help you perform these tasks in an easy way, and even package up your program for you so that others that do not use these tools also can execute the programs easily.

Answer 6

Seems to me you don't have a class named HelloWorldSWT, but rather a class named HelloWorldSWT in a package named HelloWorldSWT (youc an confirm this by going at the first line of HellowWorldSWT.java, where you will find package HelloWorldSWT;

If so, go in parent directory and type

java HelloWorldSWT.HelloWorldSWT This would work.