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If your answer was A. Compiler Error , you were correct.

What caused the compiler error?

The compiler error was caused by the code shown in Listing 2 .

Listing 2 . The code with the problem.
public static void fillIt(Collection ref){ ref.add(0,new MyClass(4));

The problem here is that the method named fillIt receives a reference to an object of the ArrayList class as the interface type Collection , and attempts to call the following overloaded method on that reference:

add(int index, Object element)

However, the Collection interface knows nothing about a method having that signature.

Implements Collection and List

The ArrayList class implements both the Collection interface and the List interface. As you may recall from earlier modules in this series, List is a sub-interface of Collection . The List interface declares the following overloaded versions of the add method:

  • add(Object o)
  • add(int index, Object element)

The second of these two methods, which is called in Listing 2 , is unknown to the Collection interface. The Collection interface declares only the first version of the add method shown above.


This is the result of specialization. A List object is a more-specialized collection than a Collection object.

Therefore, the version of the add method that requires two parameter cannot be called on a reference to an ArrayList object when that object is treated as the generic type Collection .

Modified program

Now, take a look at the modified version of the program as shown in Listing 3 .

What output is produced by the program shown in Listing 3 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. 44321
  • D. 4321
  • E. 1234
  • F. 12344
  • G. 443521
  • H. None of the above.
Listing 3 . The program named Comparable02.
//File Comparable02.java import java.util.*;public class Comparable02{ public static void main(String args[]){ new Worker().doIt();}//end main() }//end class Comparable02class Worker{ public void doIt(){Iterator iter; Collection ref;ref = new ArrayList(); Populator.fillIt(ref);iter = ref.iterator(); while(iter.hasNext()){System.out.print(iter.next()); }//end while loopSystem.out.println(); }//end doIt()}// end class Workerclass Populator{ public static void fillIt(Collection ref){((List)ref).add(0,new MyClass(4)); ((List)ref).add(1,new MyClass(4));((List)ref).add(2,new MyClass(3)); ((List)ref).add(3,new MyClass(2));((List)ref).add(4,new MyClass(1)); ((List)ref).add(3,new MyClass(5));}//end fillIt() }//end class populatorclass MyClass{ int data;MyClass(){ data = 0;}//end noarg constructor MyClass(int data){this.data = data; }//end parameterized constructorpublic String toString(){ return "" + data;}//end overridden toString() }//end MyClass

If your answer was G. 443521 , you are correct.

The corrected code

This version of the program illustrates a mechanism for correcting the problem in the earlier program shown in Listing 1 . The updated code that corrected the problem is shown in Listing 4 .

Listing 4 . The corrected code.
class Populator{ public static void fillIt(Collection ref){((List)ref).add(0,new MyClass(4)); ((List)ref).add(1,new MyClass(4));((List)ref).add(2,new MyClass(3)); ((List)ref).add(3,new MyClass(2));((List)ref).add(4,new MyClass(1)); ((List)ref).add(3,new MyClass(5));}//end fillIt() }//end class populator

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.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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