Java set up in Linux and Hello World

[WhiskyMac]

I have seen many questions about getting Hello World to work.
I have a similar problem: I used thsi code in my text editor in Ubuntu -
"public class MainTest {

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

} "

-I saved it as MainTest.java in my /home/me/ directory
-then complied it with "javac MainTest.java" to create the .class file
-then attempted to run it with "java MainTest" and also "java MainTest.java" both of which failed with error messages as follows;

Exception in thread "main" java.lang.UnsupportedClassVersionError: MainTest : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java :634)
at java.security.SecureClassLoader.defineClass(Secure ClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader .java:277)
at java.net.URLClassLoader.access$000(URLClassLoader. java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java: 212)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.j ava:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:3 21)
at sun.misc.Launcher$AppClassLoader.loadClass(Launche r.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:2 66)
Could not find the main class: MainTest. Program will exit.

-At this point there seem to be 3 files in the directory: Maintest.java , Maintest.class and Maintest.java~.

- I have tried changing the CLASSPATH to the working directory, using the CLASSPATH and -cp options in the "java" command line instruction, entering and omitting the .java file type but nothing works.

Advice required please!

[Tolls]

Nothing to do with CLASSPATH, indeed you do not (nor should ever use) that.
It has everything to do with you having two versions of Java on your system.
A 1.7 JDK and a 1.6 JRE.

[WhiskyMac]

Hi Tolls, You are right.

I googled the "Exception in Thread" error message and realsied it was because there were multiple versions of Java. I managed to find a piece of code in Ubuntu documentation that, once installed, allowed me to choose which version of Java runs. I selected the latest version and the code ran.

Thanks for your help and all the forum users whose comments pointed me in this directiopn!