Rules for Java source file.

#Rule-1

A source file can have only one public class.

          Why? - If we give public for multiple classes in single java file , It is ambiguous for JVM.
       It is ambiguous ?
  Then what exactly JVM doing with Public class ?



   - Actually whenever java program runs JVM look for the public class and inside public class search for main method.
  - When we declare multiple classes with public access modifier, JVM can't figure out  in what class to search for main method.

    How JVM get main method access  ?
    - Actually, we are giving the access to JVM by writing the access modifier named public.

public class MleClass{
  public static void main(String args[]){
    System.out.println("Hello! There?");
   }
 }

Public: When we put this  access modifier on method then this can be accessed from any class irrespective of the package.


#Rule-2

  A java source file can have any number of non-public class.
  - I think this statement straightforward.

#Rule-3.

   If the source file contains public class then file name must be same as public class.
  - I think #Rule-1 has enough explanation for this.

#Rule-4
   If th source file doesn't contain public class then  there is no naming restriction.
   

Eg:

Valid
File name: Demo.java

 class Test{
   // Some code
 }

Valid
File name: C.java

 class A{
   // Some code
 }
 class B{
   // Some code
}

Invalid
File name: C.java

 public class A{
   // Some code
 }

Invalid
File name: A.java

 public class A{
   // Some code
 }
 public class B{
   // Some code
 }

Invalid
File name: B.java

 public class A{
   // Some code
 }
class B{
  public static void main(String args[]){

  }
 }