Commons Math: java.lang.ClassNotFoundException

Question

I have this tiny bit of Java code:

import java.io.*;
import org.apache.commons.math3.linear.*;

class Test
{
    public static void main(String[] args){
        RealVector alpha= MatrixUtils.createRealVector(new double[10]);
        System.out.println(alpha.getEntry(0));      
    }
}

I can compile it successfully using javac Test.java -cp .;commons-math.jar But when I try to run it using java Test -cp .;commons-math.jar, it throws up this:

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/ma
th3/linear/MatrixUtils
        at Test.main(Test.java:9)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.math3.linear.Mat
rixUtils
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 1 more

From the Googling I did, a ClassNotFoundException usually occurs when your classpath isn't pointing to the right location. But since my code compiles, I don't see why it shouldn't execute. Any ideas?

You should have the class file and jar in the same directory — Keerthivasan, May 27 '14 at 13:06

Viorel Florian · Accepted Answer · 2016-05-09T10:54:12.943

4

If you type java into a command window you actually get how to setup a command to start a class file correctly:

Usage: java [-options] class [args...] (to execute a class) or java [-options] -jar jarfile [args...] (to execute a jar file)

"-cp" is an option so it goes before the class name

So a command script would look like this:

java -cp <SEMICOLON_SEPARETE_LIST_OF_LOCATIONS> qualified.path.to.MainClass <ARGUMENTS>

edited May 09 '16 at 10:54

answered May 27 '14 at 13:23

Viorel Florian

594
9
29

I feel quite silly. Thanks a lot. (Thanks to merlin too) – user8472 May 27 '14 at 15:54

score 3 · Answer 2 · answered May 27 '14 at 13:08

3

I just reproduced your problem, and changing the order fixes it for me.

java -cp .;commons-math.jar Test

answered May 27 '14 at 13:08

merlin2011

71,677
44
195
329

Commons Math: java.lang.ClassNotFoundException

2 Answers2