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The Collection interface declares the following two overloaded versions of the toArray method:

public Object[] toArray()public Object[]toArray(Object[] a)

In this module, will teach you how to use the first (simpler) version of the toArray method. I will also show why you need to exercise care when using the elements stored in the array to avoid corrupting the state of theobjects referred to by the elements in the collection.

I will teach you how to use the second (more complex) version of the toArray method in the next module.

Generics

The code in this series of modules is written with no thought given to Generics . As a result, if you copy and compile the code, you will probably get warnings about unchecked or unsafe operations .

While you will ultimately need to understand how to use Generics, that is a very complex topic. An understanding of Generics is beyond the scope of thiscourse. Therefore, for purposes of this course, you can simply ignore those warnings.

Discussion and sample code

Beginning with a quiz

Let's begin with a quiz to test your prior knowledge of the Collections Framework. To take this quiz, examine the program shown in Listing 1 and write down the output produced by the program.

Listing 1 . The program named ToArray01 .
//File ToArray01.java //Copyright 2001, R.G.Baldwinimport java.util.*; import javax.swing.*;public class ToArray01{ public static void main(String args[]){ new Worker().doIt();}//end main() }//end class ToArray01//===================================// class Worker{public void doIt(){ Collection ref;//Create, populate, and display the // contents of a collectionref = new LinkedList(); Populator.fillIt(ref);System.out.println("Collection contents"); showCollection(ref);//Get collection contents into the // array and display the new// contents of the array. Object[]array = ref.toArray(); System.out.println("New array contents");showArray(array); //Modify a property of an object// referred to by one of the // elements in the array. Display// array contents after // modificationSystem.out.println("Modified array contents"); ((JComponent)array[0]).setToolTipText("XX"); showArray(array);//Display the contents of the // collectionSystem.out.println("Collection contents"); showCollection(ref);}//end doIt() //-----------------------------------////Utility method for displaying // array contentsvoid showArray(Object[] array){for(int i = 0; i<array.length;i++){ if(array[i]== null){ System.out.print("null ");}else{ System.out.print(((JComponent)array[i]). getToolTipText() + " ");}//end else }//end for loopSystem.out.println();}//end showArray() //-----------------------------------////Utility method for displaying // collection contentsvoid showCollection(Collection ref){ Iterator iter = ref.iterator();while(iter.hasNext()){ System.out.print(((JComponent)iter.next()).getToolTipText() + " "); }//end while loopSystem.out.println(); }//end showCollection}// end class Worker //===================================//class Populator{ public static void fillIt(Collection ref){ref.add(new JButton()); ref.add(new JButton());ref.add(new JLabel()); ref.add(new JButton());ref.add(new JButton()); ref.add(new JLabel());Iterator iter = ref.iterator(); int cnt = 0;JComponent refVar; while(iter.hasNext()){refVar = (JComponent)iter.next(); if(refVar instanceof JButton){refVar.setToolTipText("B"+cnt++); }else{refVar.setToolTipText("L" + cnt++); }//end else}//end while loop }//end fillIt()}//end class Populator

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
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.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
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
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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