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 {
}

or

public class Foo {
}

I understand that there will be some class – visibility issues with the former example (probably it won’t be visible from other packages). But anyway, are there any reasons why someone may want to do as in the first code sample?

UPD: What cons I see in the former solution: nobody cares that it’s non-public. That class can be simply extended by some other public class in the same package later, then, non-public part of the class may bring you visibility/access issues.

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();
    }
}