Can Subclasses in Different Packages Directly Access a Superclass's Protected Members?

Understanding Protected Access in Java

In Java, the protected modifier is intended to allow access to certain members within the same package and to subclasses in other packages. However, a common misconception arises when accessing protected members from an instance of the superclass outside the subclass.

Consider the following example:

// Class A
package package1;
public class A {
    protected int protectedInt = 1;
}

// Class C
package package2;
import package1.A;
public class C extends A {
    public void go() {
        A a = new A();
        System.out.println(a.publicInt);
        System.out.println(a.protectedInt); // Eclipse underlines this line
    }
}

Eclipse raises an error on the line where a.protectedInt is accessed, claiming it is not visible. This seems to contradict the definition of protected in Java: "The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package."

Resolving the Misconception

The key to understanding this behavior lies in the definition of protected, as it only applies to subclasses. Specifically, accessing protected members is permitted only within the body of a subclass.

Therefore, the protected member protectedInt can be accessed from within Class C, but only for instances of Class C itself or instances of subclasses of Class C. It cannot be accessed directly from instances of the superclass, even though they are within the same package.

To resolve the error in the go method, you would need to create an instance of Class C instead of Class A:

C c = new C();
System.out.println(c.publicInt);
System.out.println(c.protectedInt);

This will correctly access the protected member through the subclass instance.

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