protectedのclassが何故実装できないのか `protected` public class ClassName{ // } protected class ProtectedClass{ // } class PackagePrivateClass{ // } private class PrivateClass{ // /**/ } protected

Java Language Specification - 8.1.1. Class Modifiers

> The access modifiers protected and private pertain only to member classes within a directly enclosing class declaration

Access Modifier`public``protected`
`public``protected``private`