Help to understand the issue with protected method

Question

I\'m reading Sybex Complete Java 2 Certification Study Guide April 2005 (ISBN0782144195). This book is for java developers who wants to pass java certification.

Answer 1

I am almost certain that the question meant:

"any instance of Y may call the abbey() method of any other instance of X" (not Y).

In that case it will indeed fail. To borrow the example from another answer above, the following:

package one;
public class X {
    protected void abby() {
    }
}

package other;
import one.X;
public class Y extends X {
    public void callAbbyOf(X anyOther) {
        anyOther.abby();
    }
}

will fail to compile.

The Java Language Specification explains why here: http://java.sun.com/docs/books/jls/third_edition/html/names.html#6.6.2

6.6.2.1 Access to a protected Member

Let C be the class in which a protected member m is declared. Access is permitted only within the body of a subclass S of C. In addition, if Id denotes an instance field or instance method, then: If the access is by a qualified name Q.Id, where Q is an ExpressionName, then the access is permitted if and only if the type of the expression Q is S or a subclass of S. If the access is by a field access expression E.Id, where E is a Primary expression, or by a method invocation expression E.Id(. . .), where E is a Primary expression, then the access is permitted if and only if the type of E is S or a subclass of S. (emphasis mine).