Inheritance Flashcards
How many superclasses can be specified for a subclass?
One
Can a subclass access private members of its superclass?
No. inheritance doesn’t overrule private access restriction.
Accessor methods
Provide access to private members of a class
Which constructor creates an object given class inheritance?
The superclass constructor creates the superclass portion of the object & the subclass constructor creates the subclass portion.
The superclass portion of the object is constructed automatically using its default constructor.
How can a subclass call a constructor defined by its superclass?
super()
In a multilevel hierarchy, which constructor will superclass refer to?
The constructor in the closest superclass
How can you access superclass methods?
Super()
When are constructors executed in a class hierarchy?
Constructors execute in order of derivation from superclass to subclass
Can a reference variable of a superclass be assigned a reference to an object of a subclass?
Yes
Reference variable
Used to refer to an object
Can reference variables refer to objects of different class types?
No
What members do you have access to with a superclass reference variable?
The parts of the object defined by the superclass
How do you construct a copy of an object?
Define a constructor that takes an object of the class as its parameter
Method Overriding
When a method in a subclass has the same return type and signature as a method in its superclass.
When you call an overridden method in a subclass, which method is returned?
It will always refer to the subclass method
How do you access the superclass version of an overridden method?
Use super.method()
Are methods overridden if their signatures differ?
No, they are simply overloaded.
Dynamic method dispatch
The mechanism by which a call to an overridden method is resolved at run time rather than compile time.
Known as run time polymorphism
Why is Polymorphism useful?
It allows a general class to specify methods common to all derivatives, while allowing subclasses to define the specific implementation of some or all of those methods.
Abstract Class
Defines methods for its subclasses but does not provide an implementation
Abstract Method syntax
abstract type name(parameter);
What is in the body of an abstract method?
Nothing - it has no body
Where can abstract modifiers not be used?
static methods or constructors
When must a class be declared abstract?
When it contains one or mor abstract methods
Can an abstract class have objects?
No
When a subclass inherits an abstract class, what must it do to not be declared abstract as well?
Implement all abstract methods
Final
Modifier used to prevent:
a method from being overridden
a class from being inherited
a variable from being changed
Convention for finals is upper class names
Object class Methods
Clone() equals() finalize() getClass() notify() notifyAll() toString() wait()
What is the purpose of the toString() method?
It returns a string description of the object
Many classes override this method to tailor a description of objects created
