Transcript Inheritance

It’s generally not a good idea for
programmers to work hard. I often
tell my students that they should
strive to be successfully lazy.
- David Conger
Object-Oriented Language
• Encapsulation
• Inheritance
• Polymorphism
Inheritance is the capability to derive one
class from another.
• The initial class used as the basis for the
derived class is referred to as either the base
class, parent class, or superclass.
• The derived class is referred to as either the
derived class, child class, or subclass
The Derived Class
• Is a completely new class
• Incorporates all of the behaviors and
characteristics of its base class
• Typically adds its own additional new data
and methods
• Can override any base class function
Simple Inheritance
• In simple inheritance,
each derived type has
only one immediate
base type
Circle (base class)
(derived class)
(derived class)
The Derivation Process
• Establishes a specific kind of relationship
between two classes
• This relationship is called an: is-a
• This type of relationship means that the
derived class is a more specific version of its
parent class
A Derived Class
• Has the same form as any other class, consisting
of a declaration and implementation
• However, has a distinguishing addition to the
first line of its declaration:
public class DerivedClassName extends BaseClassName
A Derived Class
If Circle is an existing class, a new class,
Cylinder can be derived as follows:
public class Cylinder extends Circle
// add additional members here
Author: Lewis/Loftus
// Demonstrates the use of the super reference.
public class Words2
//--------------------------------------------------// Instantiates a derived class and invokes its inherited and
// local methods.
//--------------------------------------------------public static void main (String[] args)
Dictionary2 webster = new Dictionary2 (1500, 52500);
Author: Lewis/Loftus
public class Book2
protected int pages;
// Sets up the book with the specified number of pages.
public Book2 (int numPages)
pages = numPages;
// Prints a message about the pages of this book.
public void pageMessage ()
System.out.println ("Number of pages: " + pages);
Author: Lewis/Loftus
public class Dictionary2 extends Book2
private int definitions;
// Sets up the dictionary with the specified number of pages
public Dictionary2 (int numPages, int numDefinitions)
super (numPages);
definitions = numDefinitions;
// Prints a message using both local and inherited values.
public void definitionMessage ()
System.out.println ("Number of definitions: " + definitions);
System.out.println ("Definitions per page: " + definitions/pages);
Access Specifications
• Private and public access specifiers have
been used to restrict access within a class
• As private access prevents access by any
non-class member, it also precludes access
by any derived class member as well
• To retain a restricted type of access across
derived classes, C++ provides a third access
specification, protected
End Inheritance