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Baldwin shows you how to extend an existing class to create a new class. The new class is the blueprint for a new type. This is the mechanism for class inheritance in Java. Inheritance provides a formal mechanism for code reuse.

Revised: Thu Mar 31 10:07:12 CDT 2016

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This module is one of a series of modules designed to teach you about the essence of Object-Oriented Programming (OOP) using Java.

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Extending a class

This module shows you how to extend an existing class to create a new class. The new class is the blueprint for a new type.

Inheritance and code reuse

The existing class is often called the superclass and the new class is often called the subclass . This is the mechanism for class inheritance in Java. Inheritance provides a formal mechanism for code reuse.

The subclass inherits all of the variables and all of the methods defined in the superclass.

Although not explicitly demonstrated in this module, whenever you declare a reference variable whose type is defined by a class, that variable can be usedto store references to objects instantiated from that class or instantiated from any subclass of that class. Furthermore, that reference can be used to callmethods defined in or inherited into that class with no requirement for a cast. If the method is defined in that class and overridden in the subclass, and ifthe object is actually of the subclass type, the overridden version will be executed. This is polymorphism.

Car radios with tape players

A class from a previous module (whose objects represent car radios) is extended to define a new class, whose objects represent expanded car radios that contain tape players. (Yes, at one point in history, car radios did contain tape players instead of CDs.)

Sending messages to the object

Objects of the new class know how to respond to messages for inserting, playing, and removing a tape, in addition to those messages that are appropriate for objects of the original Radio class.

Discussion and sample code

The three pillars of OOP

In an earlier module, I explained that most books on OOP will tell you that in order to understand OOP, you must understand the following three concepts:

  • Encapsulation
  • Inheritance
  • Polymorphism

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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