Unit 3 Cycle 2 Day 9: Error: Accessing Private Parent Fields
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Error: Accessing Private Parent Fields
Section 3.9 — Scope and Access
Key Concept
A subclass cannot directly access private fields of its superclass, even though those fields exist in the subclass object. The code super.privateField does not compile because private means private to the declaring class only. The subclass must use inherited public accessor methods to read or modify the superclass's private state. The AP exam creates error-spotting questions where a subclass method tries to read or assign a private superclass field directly. The fix is always to use the getter or setter.
Consider the following classes.
What happens when this code is compiled?
Answer: (B) Compile error in info(): name is private in Person.
name is private in Person. Even though Student extends Person, it cannot access private fields directly. Student must use getName() instead of name.
Why Not the Others?
(A) The code does not compile due to the private access violation.
(C) This is caught at compile time, not runtime.
(D) The constructor correctly uses super(n) and is valid.
Common Mistake
Private means private to the class, even from subclasses. A subclass must use public accessors to read parent data. The fix: return getName() + " grade " + grade;.
AP Exam Tip
Subclasses CANNOT access private parent fields directly. They must use public getters. This is a core encapsulation rule tested on the AP exam.