protected access requires a little more elaboration.
Suppose class A declares a protected field x and is extended by a class B, which is defined in a different package (this last point is important). Class B inherits the protected field x, and its code can access that field in the current instance of B or in any other instances of B that the code can refer to.
This does not mean, however, that the code of class B can start reading the protected fields of arbitrary instances of A!
《java in a nutshell》
protected
原文：http://www.cnblogs.com/lnas01/p/5953154.html
