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macOS Can't execute java from command line

l0uismustdie

l0uismustdie

macrumors regular
Original poster
Nov 30, 2009
109
1
Edinburgh, UK
Hello, I am attempting to run some java from my terminal and seems to be getting the following error:
Code: 
09:44@joshMac:.+rc/edu/american$ java DataLink
Exception in thread "main" java.lang.NoClassDefFoundError: DataLink
Caused by: java.lang.ClassNotFoundException: DataLink
	at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:248)

Upon reading some stuff online I found that this is an error with the java CLASSPATH. So, I tried that following:
Code: 
09:46@joshMac:.+rc/edu/american$ java DataLink -cp .
Which has the same result.

Also, when checking the classpath:
Code: 
09:50@joshMac:.+t1/edu/american$ pwd
/Users/***/Documents/school/11spr/csc546/project1/edu/american
09:50@joshMac:.+t1/edu/american$ $CLASSPATH
-bash: /Users/***/Documents/school/11spr/csc435/project/edu/american: No such file or directory

This is very odd because I have run tons of java code from my terminal so I'm not sure what could be going on here.

Any help would be much appreciated. Thanks.
 
L

lesterjune

macrumors newbie
May 12, 2009
5
0
l0uismustdie said:
Hello, I am attempting to run some java from my terminal and seems to be getting the following error:
Code: 
09:44@joshMac:.+rc/edu/american$ java DataLink
Exception in thread "main" java.lang.NoClassDefFoundError: DataLink
Caused by: java.lang.ClassNotFoundException: DataLink
	at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:248)

Upon reading some stuff online I found that this is an error with the java CLASSPATH. So, I tried that following:
Code: 
09:46@joshMac:.+rc/edu/american$ java DataLink -cp .
Which has the same result.

Also, when checking the classpath:
Code: 
09:50@joshMac:.+t1/edu/american$ pwd
/Users/***/Documents/school/11spr/csc546/project1/edu/american
09:50@joshMac:.+t1/edu/american$ $CLASSPATH
-bash: /Users/***/Documents/school/11spr/csc435/project/edu/american: No such file or directory

This is very odd because I have run tons of java code from my terminal so I'm not sure what could be going on here.

Any help would be much appreciated. Thanks.
Click to expand...

In which directory did you execute your command? And is your DataLink class part of a package?
 
l0uismustdie

l0uismustdie

macrumors regular
Original poster
Nov 30, 2009
109
1
Edinburgh, UK
I executed the javac and java commands from within the same directory as the pwd printed (/Users/***/Documents/school/11spr/csc546/edu/american)

It is part of a package and that could be my problem because that is really the only thing different between this and what I've done in the past.
 
naples98

naples98

macrumors member
Sep 9, 2008
95
3
Houston
l0uismustdie said:
I executed the javac and java commands from within the same directory as the pwd printed (/Users/***/Documents/school/11spr/csc546/edu/american)

It is part of a package and that could be my problem because that is really the only thing different between this and what I've done in the past.
Click to expand...

You will have to run the java command from the package directory. For example, if your package folder was "package" and your class was "MyClass" then you would have to run the following command inside the package directory

Code: 
java package.MyClass
 
l0uismustdie

l0uismustdie

macrumors regular
Original poster
Nov 30, 2009
109
1
Edinburgh, UK
Still no luck. If this is what you meant. My package is edu.american. So, I tried the following:
Code: 
14:41@joshMac:.+t1/edu/american$ pwd
/Users/***/Documents/school/11spr/csc546/project1/edu/american
14:41@joshMac:.+t1/edu/american$ java edu.american.DataLink
Exception in thread "main" java.lang.NoClassDefFoundError: edu/american/DataLink
Caused by: java.lang.ClassNotFoundException: edu.american.DataLink
	at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:248)

Is that what you meant?

One thing to note is these are all symbolic links
Code: 
-rw-r--r--  1 ***  ***   853 Mar  3 19:27 DataLink$ButtonListener.class
-rw-r--r--  1 ***  ***  2422 Mar  3 19:27 DataLink.class
lrwxr-xr-x  1 ***  ***    85 Feb 24 22:17 DataLink.java -> /Users/***/EclipseProjects/SlidingWindowProtocol/src/edu/american/DataLink.java
-rw-r--r--  1 ***  ***  6249 Mar  3 19:27 DataLinkHost.class
lrwxr-xr-x  1 ***  ***    89 Feb 24 22:18 DataLinkHost.java -> /Users/***/EclipseProjects/SlidingWindowProtocol/src/edu/american/DataLinkHost.java
-rw-r--r--  1 ***  ***  1454 Mar  3 19:27 Wire.class
lrwxr-xr-x  1 ***  ***    81 Feb 24 22:18 Wire.java -> /Users/***/EclipseProjects/SlidingWindowProtocol/src/edu/american/Wire.java

However, I have tried running all these commands from both locations.
 
robbieduncan

robbieduncan

Moderator emeritus
Jul 24, 2002
25,611
893
Harrogate
As per normal, standard, Java rules the .class files must be in a folder hierarchy that matches the reverse DNS package.

So in this case they should be in edu/american/ relative to the current path (or relative to any path in the CLASSPATH).
 
R

RaceTripper

macrumors 68030
May 29, 2007
2,867
178
you need to have a directory structure along the lines of

Code: 
.../build/edu/american/DataLink.class
.../build/edu/american/etc (other class files in package

Then you can execute your java command from the build directory, e.g.

Code: 
/Users/***/Documents/school/11spr/csc546/build $ java edu.american.DataLink

Your classpath needs to point to the directory that roots your package directory structure. So for the path: /Users/***/Documents/school/11spr/csc546/build/edu/american/DataLink.class

Your classpath entry needs to be: /Users/***/Documents/school/11spr/csc546/build

If you are executing java from build/ you are set since . is automatically part of the classpath (unless you set the CLASSPATH environment variable otherwise).

If you are not executing from build, then you need to set the classpath explicitly:

Code: 
java -cp /Users/***/Documents/school/11spr/csc546/build edu.american.DataLink
 
R

RaceTripper

macrumors 68030
May 29, 2007
2,867
178
robbieduncan said:
As per normal, standard, Java rules the .class files must be in a folder hierarchy that matches the reverse DNS package.

So in this case they should be in edu/american/ relative to the current path (or relative to any path in the CLASSPATH).
Click to expand...

It's more correct to say the directory structure should match the package hierarchy for defined classes. Using reverse DNS is nothing more than a convention.

So for package a.b.c.d there should be a corresponding directory structure for source files and class files (they don't have to be the same ones), e.g.
src/a/b/c/d
build/a/b/c/d
 
R

RaceTripper

macrumors 68030
May 29, 2007
2,867
178
l0uismustdie said:
Yeah I am good to go. On top of all that I forgot I had set a classpath in my .bashrc for something...

Thanks!!
Click to expand...
CLASSPATH environment variable set globally is evil. Don't do it. It will cause you nothing but grief. Use projects scripts (better yet, use Apache Ant or Maven) to set classpath locally for each project.
 
J

jhuerta50

macrumors newbie
Feb 7, 2013
2
0
RaceTripper said:
you need to have a directory structure along the lines of

Code: 
.../build/edu/american/DataLink.class
.../build/edu/american/etc (other class files in package

Then you can execute your java command from the build directory, e.g.

Code: 
/Users/***/Documents/school/11spr/csc546/build $ java edu.american.DataLink

Your classpath needs to point to the directory that roots your package directory structure. So for the path: /Users/***/Documents/school/11spr/csc546/build/edu/american/DataLink.class

Your classpath entry needs to be: /Users/***/Documents/school/11spr/csc546/build

If you are executing java from build/ you are set since . is automatically part of the classpath (unless you set the CLASSPATH environment variable otherwise).

If you are not executing from build, then you need to set the classpath explicitly:

Code: 
java -cp /Users/***/Documents/school/11spr/csc546/build edu.american.DataLink
Click to expand...


I realize this is an old post that I found. But for other new users out there, here is what I was able to do to get the java command to actually run the .class file.

I was able to cd to the directory of my .java and .class files and run both the javac and java cammands. Once I ran the java command, my program popped up an input window just as it should have.

So my terminal prompt began at (systemname:~ user$) and since my Java files are in a folder called JavaFiles, I typed this to change directory to my file location. (cd JavaFiles/Assn2) without the parenthesis of coarse.

then I was able to run both the javac and the java commands just fine without getting the Exception error when running the java command.
 
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