The theory is that someone extending your class with protected access knows more about what they are doing than someone who is merely using it with public access. They also need more access to your class’s inner workings. Other than that, protected behaves like default package access.

You can’t use a protected constructor in a class that extends the constructor’s class, other than via an implicit or explicit super() to invoke the protected constructor. In other words, you can’t say new X() in an extending class where X is the protected constructor. The following code should make it clearer: