Bug 124147

Having a public class extend a non-public class generates a warning/hint ("Exporting non-public type through public 
API"). The same should happen when a public class implements a non-public interface.


A few notes regarding the description of the hint "Exporting non-public type through public API" in the Options, which 
reads as follows:

"Checks that return types and parameter types of allpublic methods and all types of public fields are publicly 
available from other packages.Having private or package private types in a package API is useless."

– It only talks about method return and parameter types, thus the behavior for extending non-public classes is actually 
undocumented.

– The claim that "having private or package private types in a package API is useless" is not exactly true. For example 
if there is a method g() returning some non-public type and a method f() taking a parameter of that same non-public 
type, it's still valid to have a nested call f(g()) in code that doesn't have access to the type.

– There are spaces missing in "allpublic" and "packages.Having".