Changes

Inheritance is the ability for one class to use the data and methods of an ancestor class (or multiple ancestor classes if multiple inheritance is allowed), rather than having to define those again within a new class.  If class B inherits from class A, then class A is called an ancestor class of B, and class B is called a descendant class of A.

Inheritance is the ability for one class to use the data and methods of an ancestor class (or multiple ancestor classes if multiple inheritance is allowed), rather than having to define those again within a new class.  If class B inherits from class A, then class A is called an ancestor class of B, and class B is called a descendant class of A.

=== Polymorphism ===

===Polymorphism===

Polymorphism allows an object to be used in place of an ancestor object without the code that is using it having to know about the descendant. This means that a complex object can appear to be a simple one. The example below shows that you can have a specific model of car, such as the [[Model T]], which looks like and acts like a normal car.  Polymorphism can be implemented in different ways.  [[Smalltalk]] implemented it via messages.  Most compilers that support OOP implement a virtual method table, which is an array of method pointers as per the CORBA standard.  A descendant class instance can be used in place of any ancestor class instance, but an ancestor class instance cannot be used in place of a descendant class instance.

Polymorphism allows an object to be used in place of an ancestor object without the code that is using it having to know about the descendant. This means that a complex object can appear to be a simple one. The example below shows that you can have a specific model of car, such as the [[Model T]], which looks like and acts like a normal car.  Polymorphism can be implemented in different ways.  [[Smalltalk]] implemented it via messages.  Most compilers that support OOP implement a virtual method table, which is an array of method pointers as per the CORBA standard.  A descendant class instance can be used in place of any ancestor class instance, but an ancestor class instance cannot be used in place of a descendant class instance.

===Encapsulation===

===Encapsulation===

Encapsulation means that the data used by a class is defined within the class itself, rather than having to resort to global data.

Encapsulation means that the data used by a class is defined within the class itself, rather than the code having to resort to global data.  Further, functions specific to the class, called "methods" are also defined within the class.

== Classes and Instances ==

== Classes and Instances ==

A class is a definition.  In most languages, a class is a data type.  An instance is an instantiation of a class.  It can be considered in terms of a real-world analog: the designs for a pickup truck are akin to a class.  An actual pickup truck build according to those designs is an instance of that class.  The term "object" is often used to refer to either the class, an instance, or the general concept.  The data within an instance is referred to as "instance data".

A class is a definition.  In most languages, a class is a data type.  An instance is an instantiation of a class.  It can be considered in terms of a real-world analog: the designs for a pickup truck are akin to a class.  An actual pickup truck build according to those designs is an instance of that class.  The term "object" is often used to refer to either the class, an instance, or the general concept.  The data within an instance is referred to as "instance data".

==Constructors and Destructors==

==Constructors and Destructors==