Inheritance
Modern object-oriented (OO) programming languages
provide 3 capabilities:
• encapsulation - a language mechanism for restricting
access to some of the object's components.
• inheritance
• polymorphism
which can improve the design, structure and reusability of
code.
Inheritance
• Allows a new class to be based on an existing class.
• The new class inherits all the member variables and
functions (except constructors and destructors)
Inheritance
C++ class hierarchy is based upon the principle of
increased specialization.
• The base class carries attributes that are common to all
classes and virtual functions that may or may not be
overridden.
• Attributes that are esoteric to a particular entity
plane/normal or sphere/radius are not defined
• in the base class
• The derived class inherits the attributes of classes above
it in the class hierarchy
• The specialization can continue over multiple levels
Inheritance
Protection attributes: Base class member access specifiers
• public - Any holder of a pointer to an instance of the
class may invoke any public method or modify any public
data item.
• private – methods/data members may be accessed only
by methods belonging to the class
• protected - methods/data members may be access by
derived classes but not others
Inheritance
Base class
access
specifier
public
protected
private
Type of inheritance
public
protected
public in derived class.
protected in derived class.
Can be accessed directly by
member functions, friend
functions, and nonmember
functions.
Can be accessed directly
by member functions and
friend functions.
protected in derived class.
protected in derived class.
Can be accessed directly by
member functions and
friend functions.
Can be accessed directly
by member functions and
friend functions.
Hidden in derived class.
Hidden in derived class.
Can be accessed by
member functions and
friend functions through
public or protected member
functions of the base class.
Can be accessed by
member functions and
friend functions through
public or protected
member functions of the
base class.
private
private in derived
class.
Can be accessed
directly by member
functions and friend
functions.
private in derived
class.
Can be accessed
directly by member
functions and friend
functions.
Hidden in derived
class.
Can be accessed by
member functions and
friend functions
through public or
protected member
functions of the base
class.
Late Binding / Dynamic Binding
• technique of waiting until runtime to determine the
implementation of a function.
• The decision of which version of a member function
is appropriate is decided at runtime.
• Polymorphism is another word for late binding.
Polymorphism
• Enables us to write programs that process objects of
classes that are part of the same class hierarchy as if
they were all objects of the hierarchy’s base class.
Virtual Functions (C++ only)
• By default, C++ matches a function call with the
correct function definition at compile time. This is
called static binding.
• You can specify that the compiler match a function
call with the correct function definition at run time;
this is called dynamic binding.
• You declare a function with the keyword virtual if you
want the compiler to use dynamic binding for that
specific function.
Virtual Functions (C++ only)
• The virtual keyword indicates to the compiler that it
should choose the appropriate definition of f() not by
the type of reference, but by the type of object that
the reference refers to.
• Therefore, a virtual function is a member function
you may redefine for other derived classes, and can
ensure that the compiler will call the redefined virtual
function for an object of the corresponding derived
class, even if you call that function with a pointer or
reference to a base class of the object.
Virtual Functions (C++ only)
• A class that declares or inherits a virtual function is
called a polymorphic class.
• You redefine a virtual member function, like any
member function, in any derived class.