4 classes in one program..how to

I have this program..,

interface Inter
{
public void amethod();
}
class NoInstance
{
}
class Instance implements Inter
{
public void amethod()
{
System.out.println("Print");
}
}
public class SubInstance extends Instance
{
public static void main(String[] args)
{
Instance inst = new Instance();
SubInstance subinst = new SubInstance();
NoInstance noinst = new NoInstance();
System.out.println((inst instanceof Inter));
System.out.println((subinst instanceof Inter));
System.out.println((noinst instanceof Inter));
}
}

I am relatively new to java. How do u compile the above program(i know it is javac file name), but the above code has got three classes like NoInstance, Instance and subInstance and interface.what should be the name of the program NoInstance.javaor Instance.java or subInstance.java
i tried with subInstance.java it is working., can u please clarify because all the three classes are different(i mean not inner classes)
can u please explain this
------------------
Reddy

you can have as many classes as you like in one source file but only one public class per source file
and it is the public class that you must use to save the file as the public classes name and to compile it

can the classes above the public classes be private? i.e
in the above program, classes like Instance, no instance can
they be private

they can be anything you want them to be they are totally seperate classes the compiler will break them up in to 3 diffrent class files

Hi,
i think you can't apply 'private' or 'protected' access modifier to the top level classes.
any comment from java expert would be appreciated.
vivek

Yes, Vivek you are right. Top level classes cannot be private or protected. They can either be public or the default(i.e no access modifier).
Suma

protected cannot be used for classes only for methods

And...
When we use default (also called "friendly") for one class, every class in the current directory can access this. It happens because Java assumes that all classes in the same directory belongs to the same package.
So, if we write code in the same directory, as many people does; for these classes, it doesn�t matter if we define them as friendly or as public.
Adrian

Fred- you're thinking only of top-level classes. It's entirely possible to have a protected inner class. Also fields (member variables) can be protected as well - not just methods.