AP Computer Science A:: Inheritance

What is INHERITANCE in object-oriented programming?

- **A)** A mechanism where two classes share no relationship at all
- **B)** Copying and pasting a class's entire code into a new, unrelated class
- **C)** A mechanism where a new class (the SUBCLASS) is defined based on an EXISTING class (the SUPERCLASS), automatically gaining that superclass's instance variables and methods, while being able to add or override its own
- **D)** A synonym for encapsulation

What Java keyword is used to declare that one class INHERITS from another, such as \(public\ class\ Dog\ extends\ Animal\)?

- **A)** \(implements\)
- **B)** \(super\)
- **C)** \(inherits\)
- **D)** \(extends\)

In the relationship \(public\ class\ Dog\ extends\ Animal\), which class is the SUPERCLASS and which is the SUBCLASS?

- **A)** This relationship does not establish any superclass/subclass distinction
- **B)** \(Dog\) is the superclass, and \(Animal\) is the subclass (the reverse of the truth)
- **C)** Both classes are considered superclasses
- **D)** \(Animal\) is the SUPERCLASS (the more general, parent class), and \(Dog\) is the SUBCLASS (the more specific, child class)

What does a SUBCLASS automatically GAIN from its SUPERCLASS through inheritance?

- **A)** Only the superclass's \(private\) instance variables, nothing else
- **B)** The subclass replaces the superclass entirely, gaining none of its own identity
- **C)** The superclass's \(public\) and \(protected\) instance variables and methods (though NOT its \(private\) members, which remain inaccessible directly)
- **D)** Absolutely nothing; inheritance provides no automatic access to anything

What is the purpose of the \(super\) keyword when used to call \(super(...)\) as the FIRST line of a subclass's constructor?

- **A)** It deletes the superclass's version of the object
- **B)** It explicitly calls the SUPERCLASS's constructor, allowing the superclass's portion of the object's state to be properly initialized before the subclass's own constructor code runs
- **C)** \(super(...)\) can only be used inside a subclass's methods, never inside its constructor
- **D)** It creates an entirely separate, second object of the superclass

If a subclass's constructor does NOT explicitly call \(super(...)\), what does Java do automatically?

- **A)** Java automatically inserts an IMPLICIT call to the superclass's NO-ARGUMENT constructor as the very first statement, before the subclass's own constructor code runs
- **B)** Java calls the subclass's OWN constructor twice instead
- **C)** This causes a compile-time error in every case
- **D)** Java skips initializing the superclass portion of the object entirely

What is METHOD OVERRIDING, as distinguished from method OVERLOADING (Unit 5)?

- **A)** Defining multiple methods with the same name but different parameter lists within the SAME class
- **B)** Overriding and overloading are always exactly the same thing with no distinction
- **C)** Overriding requires the subclass method to have a DIFFERENT name from the superclass method
- **D)** A SUBCLASS providing its OWN implementation of a method that is already defined in its SUPERCLASS, using the EXACT SAME method signature (name and parameter list), to REPLACE (not add to) the inherited behavior

What is the purpose of the \(@Override\) ANNOTATION placed above a method definition, such as: \(@Override\ public\ String\ toString()\ \{\ ...\ \}\)?

- **A)** \(@Override\) is required for a method to actually override anything -- without it, overriding does not occur at all
- **B)** \(@Override\) can only be used on constructors
- **C)** It tells the COMPILER that this method is INTENDED to override a superclass method, so the compiler can catch a mistake (like a typo in the method's name or parameters) that would otherwise silently create an unrelated new method instead
- **D)** \(@Override\) changes the method's return type automatically