<< Chapter < Page Chapter >> Page >

An array is a container

As you should already know, an array is a container that can be used to store a collection of primitive values or a collection of references to objects.

The Collection interface declares a method named toArray , which can be called on a Collection object to "return an array containing all of the elements in this collection whose runtime type is that of thespecified array" .

An opportune time

Since you are studying this sub-series of modules to learn about the uses of the Comparator interface, this seems like an opportune time to teach you how to get an array from a collection, and how to use the Comparator interface to sort the contents of the array. (While I'm at it, I will also teach you how to sort the elements in an array of object references into naturalorder without the use of a Comparator object.)

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

See if you can write down the output produced by the program shown in Listing 1 .

Listing 1 . The program named Comparator 05 .
//File Comparator05.java //Copyright 2001, R.G.Baldwinimport java.util.*; import java.io.Serializable;public class Comparator05{ public static void main(String args[]){ new Worker().doIt();}//end main() }//end class Comparator05class Worker{ public void doIt(){Iterator iter; Collection ref;Object[] array;ref = new Vector(); Populator.fillIt(ref);iter = ref.iterator(); System.out.println("Collection data");while(iter.hasNext()){ System.out.print(iter.next() + " ");}//end while loop System.out.println();array = ref.toArray(); System.out.println("Raw array data");display(array); //Sort the array into natural order// and display it.Arrays.sort(array); System.out.println("Natural order sorted " +"array data"); display(array);//Sort the array into custom order // and display it.Arrays.sort(array, new TheComparator()); System.out.println("Custom order sorted " +"array data"); display(array);iter = ref.iterator(); System.out.println("Collection data");while(iter.hasNext()){ System.out.print(iter.next() + " ");}//end while loop System.out.println();}//end doIt() static void display(Object[]array){ for(int i = 0; i<array.length;i++){ System.out.print(array[i]+ " "); }//end for loopSystem.out.println(); }//end display()}// end class Worker class Populator{public static void fillIt(Collection ref){ ref.add("Joe");ref.add("Bill"); ref.add("Tom");ref.add("JOE"); ref.add("BILL");ref.add("TOM"); }//end fillIt()}//end class Populator class TheComparator implements Comparator,Serializable{public int compare(Object o1,Object o2){ if(!(o1 instanceof String))throw new ClassCastException(); if(!(o2 instanceof String))throw new ClassCastException(); int result = ((String)o1).compareTo(((String)o2));return result*(-1); }//end compare()}//end class TheComparator

Questions & Answers

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 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
How can I make nanorobot?
Lily
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
how can I make nanorobot?
Lily
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





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
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?

Ask