[prog] Errors using JDK

[David Sumbler]

Wishing to learn Java, I am using http://math.hws.edu/javanotes/ .  I
run Ubuntu 7.10, and I have installed Sun JDK 5.0 from Ubuntu.  Version
6.0 is also available, but as the book only assumes 5.0, and the J2RE I
had already was 5.0, I thought I would perhaps be spared problems by
sticking with 5.0.

Compiling programs using 'javac' seems to work OK, but when I try to run
them using 'java', I get the following:

Exception in thread "main" java.lang.UnsupportedClassVersionError:
HelloWorld (Unsupported major.minor version 49.0)
        at java.lang.ClassLoader.defineClass0(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:539)
        at
java.security.SecureClassLoader.defineClass(SecureClassLoader.java:123)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:251)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:55)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:194)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:187)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:289)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:274)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:235)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:302)

Obviously the name of the program varies, but otherwise the messages are
always the same.  The problem, I assume, is in "Unsupported major.minor
version 49.0".

Could someone tell me what I need to do to solve this, please?

David

-- 
David Sumbler <david at aeolia.co.uk>