Unit 3 Cycle 1 Day 25: Inheritance: Method Availability

February 18, 2026

Unit 3 Foundation (Cycle 1) Day 25 of 28 Foundation

Inheritance: Method Availability

Section 3.12 — Inheritance Basics

Key Concept

Inheritance determines which methods are available to a subclass, but private members of the superclass are not directly accessible. A subclass inherits all public and protected methods but cannot access private instance variables directly — it must use inherited getters and setters. The AP exam tests whether a method call on a subclass object is valid by checking: is the method defined or inherited? A method defined only in the subclass cannot be called through a superclass reference without casting.

Consider the following hierarchy.

public class Appliance { public void turnOn() { /* ... */ } public void turnOff() { /* ... */ } } public class Washer extends Appliance { public void wash() { /* ... */ } }

Which methods can be called on a Washer object?

Answer: (B) turnOn(), turnOff(), and wash()

Washer inherits turnOn() and turnOff() from Appliance and adds its own wash(). A subclass has all parent methods plus its own.

Why Not the Others?

(A) Washer also inherits turnOn() and turnOff() from Appliance.

(C) Washer has its own wash() method in addition to inherited methods.

(D) No casting is needed. The Washer object has direct access to all three methods.

Common Mistake

A subclass inherits ALL public methods from its parent. It can also add new methods. The subclass has the union of parent methods and its own methods.