Inheritance in Object-Oriented Programming

Study Notes

Inheritance is a mechanism for creating new classes (derived classes) based on existing classes (base classes).
Derived classes inherit properties and behaviors from base classes.
Base class elements can be accessed using the scope operator. e.g., BaseClassName::elementName.
Inheritance limits the visibility of elements of the base class. Elements marked protected can be accessed by the derived class and other classes in the same package but not directly by users. Private elements are only accessible by the class they are defined in.
Derived classes can redefine behaviors of inherited members.
Constructors of the base class are called before those of the derived class.
Destructors of the base class are called after those of the derived class.

Examples of inheritance include geometric shapes (square, rectangle, circle, triangle) with common properties.
Each shape type has its own attributes (e.g., square: side, rectangle: width and height, circle: radius, triangle: points A, B, and C).
Base and derived classes have members (data).
Base classes define public, private, and protected members.
Example methods include drawing, erasing, and calculating area for each shape type.

A Figure (base class) is the most general class that is the parent to specific shape classes.
Derived classes (e.g., Square, Rectangle, Circle, Triangle) are specialized shapes.
Base class member functions are inherited by derived classes.
Derived classes can redefine (override) base class member functions.

Class Figure has a private Point center member. A public method Point& getCenter() retrieves the center.
Public Method void draw() and void erase()
Class Circle inherits from Figure, adding a double radius member.
The Circle class redefines the virtual draw function in the Figure class to provide a drawing action specific to circles.
The constructor and destructor for the derived class do not inherit those of the base class.

Types of Inheritance: public, private, protected
Members of the base class are visible to those of a derived class (private, protected, and public). The visibility of members of the base class depends on the visibility modifier of the base class member, and the type of inheritance.

The derived class constructor initializes the base class members first, then derived-class members.
Base-class constructors are always called before derived-class constructors.

The destructor of the derived class is called after the destructor in the opposite order.
Base-class destructors are called last.

Example code demonstrates how to create instances of Figure, Circle, Rectangle, etc.
Methods (draw, getSides()) are called on objects.
Functions, like compare, take Figure& arguments, to ensure correct use even in a polymorphic situation.

Polymorphism allows objects of different classes to be treated as objects of a common type.
This is useful for handling a diverse set of objects uniformly.
Method resolution is determined by the actual object type at run-time.

Virtual functions are declared in a base class and can be redefined in derived classes.
Virtual functions allow polymorphism because the correct derived class functions are called based on the object type at run-time.
The virtual keyword is only required in the base class definition, not in the derived-class redefinitions.

Abstract classes cannot be instantiated directly.
They serve as base classes for defining common behaviors.
A pure virtual function (declared as = 0) signals that the function must be implemented in any derived class.

A class can inherit from multiple base classes.
The order of derivation is important for initialization and cleanup.
Ambiguity resolution may be required if there are name collisions. This is often addressed with virtual inheritance.

The iostream library provides input/output functionality in C++.
Input and output are handled through streams.
Class ios is the base class in the iostream hierarchy.
Derived classes (iostream, ofstream, ifstream, istringstream, ostringstream) handle I/O with different types of media.

Manipulators are functions/classes used with insertion and extraction operators (<<, >>) to affect how data is formatted/processed. An example would be formatting numbers in a specific way, or conversion from numeric to string for display.