[CentOS] Error: Could not find or load main class with OpenJDK and Oracle Java

[Alexander Farber]

Hello fellow Linux users,

on CentOS 7.2 I have successfully downloaded and installed Oracle Java [1]
with:

# rpm -Uvh jdk-8u91-linux-x64.rpm

Also there is already OpenJDK installed:

# rpm -qa | grep -i jdk
java-1.8.0-openjdk-headless-1.8.0.91-0.b14.el7_2.x86_64
java-1.8.0-openjdk-1.8.0.91-0.b14.el7_2.x86_64
jdk1.8.0_91-1.8.0_91-fcs.x86_64

I can switch between the 2 using this command:

# alternatives --config java

There are 2 programs which provide 'java'.

  SelectionCommand
---
*  1
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.91-0.b14.el7_2.x86_64/jre/bin/java
 + 2 /usr/java/jdk1.8.0_91/jre/bin/java

Enter to keep the current selection[+], or type selection number:

And see the selected version with:

# java -version
java version "1.8.0_91"
Java(TM) SE Runtime Environment (build 1.8.0_91-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.91-b14, mixed mode)

# javac -version
javac 1.8.0_91

Now to my problem please -

I have created a simple java file named TheClassName.java:

package thepackagename;

public class TheClassName {
public static final void main(String[] args)  {
System.out.println("Hello World!");
}
}

After successfully compiling it with "javac TheClassName.java"
(which produces TheClassName.class file in the same dir)
I unfortunately can not run it:

# java -cp . thepackagename.TheClassName
Error: Could not find or load main class thepackagename.TheClassName

Here another try:

# export
JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.91-0.b14.el7_2.x86_64/jre

# $JAVA_HOME/bin/java -cp . thepackagename.TheClassName
Error: Could not find or load main class thepackagename.TheClassName

Setting another environment variable does not help either:

# export CLASSPATH=.

Similar command on Windows 7 works well and I have tried
copying the TheClassName.class file from there to Linux too.

The setting is SELINUX=disabled and the server
was installed few weeks ago, serving (without errors) as
LAMP with MySQL/PostgreSQL/Apache/WordPress.

Any suggestions please, have I missed anything?

Regards
Alex

  [1]: http://www.oracle.com/technetwork/java/javase/
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Re: [CentOS] Error: Could not find or load main class with OpenJDK and Oracle Java

[Alexander Farber]

Nevermind, I had to move my test file under
thepackagename/TheClassName.class and then it runs fine.

However my real program [1] consisting of few jar-files still
does not run on CentOS (while running fine on Windows).

I have to investigate more and will ask a separate question.

Regards
Alex

[1]: https://github.com/afarber/jetty-newbie/tree/master/WebsocketHandler
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