http://837062099.iteye.com/blog/1609340
protected修改的属性和方法：
相同：在同一个包中访问的时候和public、default修饰是一样的
不同：在包外访问的时候要遵循一个原则
But a subclass in another package can access the protected members in the super-class via only the references of subclass or its subclasses. A subclass in the same package doesn’t have this restriction. This ensures that classes from other packages are accessing only the members that are part of their inheritance hierarchy.
1、在包外要访问protected修饰的member，那么这个包外要试图去访问protected修饰的member的类一定要是member所在类的子类或者子类的子类...
2、只有通过这个包外类的引用或者其子孙类的引用才能访问到那个protected修饰的member
这个引用包括this.method()