Why Can't I Access a Superclass's Protected Member from a Different Package in Java?

Understanding Java's Protected Modifier and Its Accessibility Restrictions

The protected access modifier in Java often leads to confusion regarding its intended usage. One such instance arises when trying to access a protected member of a superclass from a different package.

In the provided example, Class A contains an instance variable protectedInt declared with protected access. According to Oracle documentation, protected members should be accessible within the same package or subclasses of their class in other packages. However, when Class C (extending Class A) tries to access protectedInt, Eclipse reports the error "A.protectedInt" is not visible.

The reason for this error lies in the correct interpretation of the protected access modifier. Protected access permits using protected members within the class declaring them and only within subclasses of that class, regardless of the package they belong to.

To illustrate, this code snippet works as intended:

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

This is because the type of c is an instance of C, which is a subclass of A. However, if c were an instance of A, accessing protectedInt would not be possible.

This behavior aligns with the Java Language Specification (JLS) section 6.6.2, which states that a protected member can only be accessed within subclasses, and if the access is via field access or method invocation expression, the type of the object must be the subclass or a further subclass.

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