Non-public top level class in Java

Question

What\'s the reason of making top-level class non-public in Java?

Let\'s say we have Foo.java, there could be

class Foo {
}

Answer 1

Here is an example. No one needs to know about existence of our ConcreteDocument.

DocumentIF.java

public interface DocumentIF {
}

ConcreteDocument.java

class ConcreteDocument implements DocumentIF {
}

DocumentFactory.java

public class DocumentFactory {
    public DocumentIF createDocument() {
        return new ConcreteDocument();
    }
}