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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.)


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

who was the first nanotechnologist
Lizzy Reply
technologist's thinker father is Richard Feynman but the literature first user scientist Nario Tagunichi.
Norio Taniguchi
I need help
anyone have book of Abdel Salam Hamdy Makhlouf book in pdf Fundamentals of Nanoparticles: Classifications, Synthesis
Naeem Reply
what happen with The nano material on The deep space.?
pedro Reply
It could change the whole space science.
the characteristics of nano materials can be studied by solving which equation?
sibaram Reply
plz answer fast
synthesis of nano materials by chemical reaction taking place in aqueous solvents under high temperature and pressure is call?
hydrothermal synthesis
how can chip be made from sand
Eke Reply
is this allso about nanoscale material
are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
where is the latest information on a no technology how can I find it
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
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
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
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
STM - Scanning Tunneling Microscope.
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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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