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Interface type is not used

The program makes no use of the interface as a type, and exhibits no polymorphic behavior (no decision among methods having the same signature is required) .

The class named A inherits an abstract method named intfcMethod from the interface and must define it. (Otherwise, it would be necessary to declare the class named A abstract.)

The interface is not a particularly important player in this program.

Back to Question 3

Answer 2

A. Compiler Error

Explanation 2

Simple hierarchical polymorphic behavior

This program is designed to test your knowledge of simple hierarchical polymorphic behavior.

Implement the interface named X

This program defines a class named A that extends a class named Base , and implements an interface named X , as shown in the following code fragment.

class A extends Base implements X{ public void inherMethod(){System.out.print( " A-inherMethod ");}//end inherMethod()public void intfcMethod(){ System.out.print("A-intfcMethod ");}//end intfcMethod() }//end class Ainterface X{ public void intfcMethod();}//end X

Override and define some methods

The class named A overrides the method named inherMethod , which it inherits from the class named Base . It also provides a concrete definition of the method named intfcMethod , which is declared in the interface named X .

Store object's reference as superclass type

The program instantiates an object of the class named A and assigns that object's reference to a reference variable of type Base , as shown in the following code fragment.

Base myVar2 = new A();

Oops! Cannot call this method

So far, so good. However, the next fragment shows where the program turns sour. It attempts to call the method named intfcMethod on the object's reference, which was stored as type Base .


Polymorphic behavior doesn't apply here

Because the class named Base does not define the method named intfcMethod , hierarchical polymorphic behavior does not apply. Therefore a reference to the object being stored as type Base cannot be used to directly call the method named intfcMethod , and the program produces a compiler error.

What is the solution?

Hierarchical polymorphic behavior is possible only when the class defining the type of the reference (or some superclass of that class) contains a definition for the method that is called on the reference.

There are a couple of ways that downcasting could be used to solve the problem in this case.

Back to Question 2

Answer 1

A. Compiler Error

Explanation 1

I put this question in here just to see if you are still awake.

Can store reference as interface type

A reference to an object instantiated from a class can be assigned to any reference variable whose declared type is the name of an interface implementedby the class from which the object was instantiated, or implemented by any superclass of that class.

Define two classes and an interface

This program defines a class named A that extends a class named Base . The class named Base extends Object by default.

The program also defines an interface named X .

Instantiate an object

The following statement instantiates an object of the class named A , and attempts to assign that object's reference to a reference variable whosetype is the interface type named X .

X myVar2 = new A();

Interface X is defined but not implemented

None of the classes named A , Base , and Object implement the interface named X . Therefore, it is not allowable to assign a reference to an object of the classnamed A to a reference variable whose declared type is X . Therefore, the program produces the following compiler error under JDK 1.3:

Ap131.java:20: incompatible types found : Arequired: X X myVar2 = new A();

Back to Question 1


Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
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
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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