If this program isn't for a course or isn't an exercise of some sort,
the following paragraph does not really apply to you.

I'd hate to discover I was cheating you out of learning for a course by
telling you the answer, but maybe this will help you learn the
fundamentals better.

I can't tell what you're asking in question 1, have you thought about
this thoroughly? Are you trying to run both with one command?

If so, you could possibly put in the first one, the one you want to run
from the command prompt, a line telling the other class to run.

That is, if your classes were something like

    public class A
    {
         public static void main(String[] args)
         {
              System.out.println("Class A is running");
         }
    }

and an identical one with B instead of A, you could put instead for A:

    public class A
    {
         public static void main(String[] args)
         {
              System.out.println("Class A is running");
              B.main(args);
         }
    }

To see whether there was an input or not, you can do this: pretend your
code looks like the following, and has an additional
isPalindrome(String s) method.

    public class B
    {
         public static void main(String[] args)
         {
              if(args == null)
                   System.out.println("No input!");
              else
              {
                   String wholestring = "";
                   for(int i = 0; i < args.length; i++)
                        wholestring += args[i];
                   if(isPalindrome(wholestring))
                        System.out.println("A palindrome");
                   else
                        System.out.prinltn("Not a palindrome");
              }
         }
         //also there should be a boolean method
"isPalindrome(String)"
    }

Sub: Question:

1st point.  A title of 'Question:' is not very helpful.
This post should ideally be split into two parts, the
first titled (something like) 'Run from command prompt'.

Note that title does not mention 'question' or 'problem'
or 'help', which is almost assumed, and the body of the
message can make clear, in any case.

I will deal with only the first, on this thread.

...

(good illustration)
The code above shows two classes File and Main,
both with no attributes, and no *methods*, let alone
a method called main (that is of the right form to
be understood as *the* main(String[] args) method
that the JVM looks for, to start a class).

The JVM understands that any class to be loaded
and run has a 'main', so ..

..here it reports it was unable to find that 'main' method.

Google for HelloWorld in Java and it should show
a valid form for the main.

As an aside, an excellent group for those beginning
Java, is comp.lang.java.help

HTH

Andrew T.