Files with no public classes can have a name that does not match any of the classes in the file.

if you declare a class A in a file called X.java as follows ::

class A{

------

}

the class will compile correctly.

But if you declare the class A as ::

public class A{

}

this will result in an error as --- ( class A is public, must be declared in a file A.java )

This comes under Source File Declaration Rules as defined by java Developers.