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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

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.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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 did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit 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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