When trying to run  a java  program, you ommit the ".class" at the end of
the class name e.g.

java myfile

assuming that the class myfile.class is in your current directory and
myfile.class does not specifiy a package e.g. package com.tld.abc;

If you have specified myfile to be in package com.tld.abc then the command
would be

java com.tld.abc.myfile

Add exception  for invalid number.
You seems to be using C syntax for printf, check out System.out.println
API

printf is not a Java function. Use print or println
instead. See the Java SDK docs for more info.

Other than that, what problems are you having?

Java 5 does have printf() (see PrintStream and PrintWriter).

To post authors: please tell us what JDK you are working with in order
to receive accurate responses.