java compile command line

Question

I wrote a program in the Intellij IDEA. It runs fine in the IDE but I am having problems with it from the command line (I so very rarely run my own from the command line I think I am just missing a step.) So here is the problem. If I navigate to where my file is:

cd averageAmpCov/src/

and then run my program it works fine:

java averageAmpCov

Error: Parameter 'out' is required.
Error: Parameter 'in' is required.
Usage: java averageAmpCov
       (-o|--outputlocation) <out> (-i|--inputlocation) <in>

  (-o|--outputlocation) <out>
        Where is the input file to be put? Full path and desired file name

  (-i|--inputlocation) <in>

But when I try to run from outside the folder like this:

java averageAmpCov/src/averageAmpCov

I get a sad error:

Exception in thread "main" java.lang.NoClassDefFoundError: averageAmpCov/src/averageAmpCov (wrong name: averageAmpCov)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:792)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)

Some other posts say that it might be a class path problem, but I am not really understanding what to do. What am I doing wrong here?

Answer 1

When attempting to run your program outside the class folder, set the classpath to the directory in which your .class file is located:

java -cp averageAmpCov/src averageAmpCov

Now you won't get a NoClassDefFoundError . The classpath is where Java looks to find .class files to load and run. The class name argument must be the actual class name, no directories involved.

Answer 2

To use java correctly, you should ensure that:

1. You use the fully-qualified class name of the main class.
2. The main class should be in the classpath.

The classpath can be set in 3 ways:

1. It can be set within the environment variable CLASSPATH .
2. With the option -cp which would overwrite CLASSPATH .
3. If you don't use neither, then the current directory is the classpath.

Note that if the structure of the files as follows:

bin -
     |
     com -
         |
         mypackage -
                   |
                   Hello.class

and Hello 's package name is com.mypackage , then the following command should work:

java -cp C:\projects\myprojct\bin com.mypackage.Hello

Alternatively, you can cd to C:\\projects\\myprojct\\bin and just use:

java com.mypackage.Hello

Answer 3

Running this is fine

java averageAmpCov/src/averageAmpCov

BUT i guess u forgot to set ur classpath set class path first