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As a result, the users of the concrete implementations in the Java Collections Framework don't need to know any of the implementation details of the collection to create and use an iterator. All of the work necessary to properly create an iterator is done by the author of the class that implements the appropriate Collection interfaces. All the user needs to understand is the behavior of the three methods declared in the Iterator interface.


Polymorphic behavior, based on the Java interface, is one of the most important concepts in Java OOP

In this module, I began my discussion of runtime polymorphism as implemented using method overriding and the Java interface.

I presented a simple skeleton program that illustrated many of the important aspects of polymorphic behavior based on the Java interface.

By using a nonstandard notation of my own design, (a totally abstract class) , I explained how the implementation of interfaces in Java is similar to multiple inheritance.

I explained the cardinal rule, which is:

If a class implements an interface, it must provide a concrete definition for all the methods declared by that interface, and all the methods inherited by that interface. Otherwise, the class must be declared abstract and the definitions must be provided by a class that extends the abstract class.

I explained that objects instantiated from classes that implement the same interface have a new relationship that goes beyond the relationship imposed by the standard class hierarchy.

I explained that due to the combination of the class hierarchy and the fact that a class can implement many different interfaces, a single object in Java can be treated as many different types. However, for any given type, there are restrictions on the methods that can be called on the object.

I also explained that because different classes can implement the same interface, objects instantiated from different classes can be treated as a common interface type.

I suggested that there is little if anything useful that can be done in Java without understanding and using interfaces.

Finally I discussed some real-world examples of the use of the Java interface:

  • Delegation event model
  • Model View Control paradigm
  • Bound and constrained properties in JavaBeans Components
  • Java Collections Framework Iterators and Enumerators

What's next?

In the next module, I will explain a more substantive program as I continue my discussion of polymorphic behavior using the Java interface.


This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Java OOP: Polymorphism and Interfaces, Part 1
  • File: Java1616.htm
  • Published: 03/27/02

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have misappropriated copies of my modules from cnx.org, converted them to Kindle books, andplaced them for sale on Amazon.com showing me as the author. I receive no compensation for those sales and don't know who doesreceive compensation. If you purchase such a book, please be aware that it is a bootleg copy of a module that is freelyavailable on cnx.org.

Affiliation :: I am a professor of Computer Information Technology at Austin Community College in Austin, TX.

Complete program listings

A complete listing of the sample program is shown in Listing 6 below.

Listing 6 . Complete program listing.
/*File Poly05.java Copyright 2002, R.G.Baldwin**************************************/ interface I1{public void p(); }//end interface I1//===================================// interface I2 extends I1{public void q(); }//end interface I2//===================================// class A extends Object{public String toString(){ return "toString in A";}//end toString() //---------------------------------//public String x(){return "x in A"; }//end x()//---------------------------------// }//end class A//===================================// class B extends A implements I2{public void p(){ }//end p()//---------------------------------//public void q(){ }//end q();//---------------------------------// }//end class B//===================================// class C extends Object implements I2{public void p(){ }//end p()//---------------------------------//public void q(){ }//end q();//---------------------------------// }//end class B//===================================// public class Poly05{public static void main(String[] args){}//end main }//end class Poly05


Questions & Answers

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
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.
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