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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:
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.
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.
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 |
-end-
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