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Corresponding to the above notions, abstract classes in Java cannot be instantiated. Abstract classes are denoted by the abstract keyword in the class definition: public abstract class AFruit {...} By convention, the classnames of abstract classes always begin with "A".

In Ballworld, ABall is an abstract class representing a circular ball that has a number of properties: a color, a position, a velocity, etc. The abstract ball also has some defining behaviors, such as that all balls should paint a filled, colored circle when requested to display themselves on a graphics context (a panel). Likewise all balls know how to bounce off the walls of the container. These concrete behaviors are called "default behaviors" because all subclasses of ABall , such as StraightBall and CurveBall , automatically get these behaviors by default. One of the most common and useful reasons for using an abstract class is to be able to define the default behaviors for all the subclasses.

Abstract methods

But what about the abstract behaviors that abstract classes exhibit? For instance the abstract "ripening" behavior of a fruit? At the abstraction level of a fruit, the exact implentation of ripening cannot be specified because it varies from one concrete subclass to another. In Java, this is represented by using the keyword abstract as part of the signature of a method which has no code body: public abstract class AFruit { // rest of the codepublic abstract void ripen();} There is no code body because it cannot be specified at this abstraction level. All that the above code says is that the method does exist in all AFruit . The specific implmentation of method is left to the subclasses, where the method is declared identically except for the lack of the abstract keyword: public class Mango extends AFruit { // rest of codepublic void ripen() {// code to ripen a mango goes here }}public class Tomato extends AFruit { // rest of codepublic void ripend() {// code to ripen a tomato goes here }} The technical term for this process is called overriding . We say that the concrete methods in the subclasses override the abstract method in the superclass.

Note that if a class has an abstract method, the class itself must be declared abstract . This simply because the lack of code in the abstract method means that the class connot be instantiated, or perhaps more importantly, it says that in order for a class to represent abstract behavior, the class itsefl must represent an abstract notion.

Overriding is not limited to abstract methods. One can override any concrete method not declared with the final keyword. We will tend to avoid this technique however, as the changing of behavior as one changes abstraction levels leads to very unclear symantics of what the classes are actually doing.

In Ballworld we see the abstract method updateState . Abstract methods and classes are denoted in UML diagrams by italic lettering. This method is called by the update method as part of the invariant process of updating the condition of the ball every 50 milliseconds. The update method does 4 things:

  1. Update the state of the ball by calling the abstract updateState method.
  2. Move (translate) the position of the ball by adding the velocity to it.
  3. Check if the ball needs to bound off a wall.
  4. Paint the ball up on the screen.
This technique of calling an abstract method from inside of a concrete method is called the template method design pattern --which we will get to later in the course.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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Source:  OpenStax, Principles of object-oriented programming. OpenStax CNX. May 10, 2013 Download for free at http://legacy.cnx.org/content/col10213/1.37
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