Why Does Eclipse Flag Protected Field Access as Invalid in Java Inheritance?

Understanding Java's Protected Modifier

Eclipse's Confusion over Protected Access

When examining a class hierarchy, Eclipse mistakenly flags the access of a protected field as invalid. This apparent contradiction arises from a misunderstanding of the intended functionality of the protected modifier.

According to the Java Language Specification (JLS), a protected member is accessible within the declaring class's package and by subclasses of that class, regardless of the subclass's package. In this case, class A declares the protected field protectedInt.

Issue Analysis

In the given example, class C extends class A, which means that C instances should have access to A's protectedInt field. However, Eclipse reports that the access is prohibited when using an instance of A in C.

Resolving the Discrepancy

The solution lies in understanding that protected access is restricted to subclasses of the declaring class. Therefore, A's protectedInt field can only be accessed by instances of C or subclasses of C. This is a crucial distinction that Eclipse misses.

To illustrate, accessing protectedInt through an instance of C would work as intended:

C c = new C();
System.out.println(c.protectedInt); // Access to 'protectedInt' allowed

Ultimately, the protected modifier provides controlled access to fields and methods, allowing them to be inherited by subclasses while maintaining encapsulation within a package.

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