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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

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
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..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
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.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
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
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
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.
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