you declare that a class member has default accessibility (because you did not specify public,protected, or private)
This kind of accessibility is called package accessibilty. That's to say: only classes in same package can acces this class members. Classes in other packages can't, no matter that they inherit from this class which declared that public accessibility member. Now try this to see what happens? Declare an abstract class which has an abstract method with default accessibility. Now make anothe class in other package inherit from this one. What will happen, since the abstract method is not accessible for the inherite class?