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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.)

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 mutation
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what is a cell
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classification of plants, gymnosperm features.
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urine is formed in the nephron of the renal medulla in the kidney. It starts from filtration, then selective reabsorption and finally secretion
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State the evolution relation and relevance between endoplasmic reticulum and cytoskeleton as it relates to cell.
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malaria is caused by an insect called mosquito.
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Malaria is cause by female anopheles mosquito
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Malaria is caused by plasmodium Female anopheles mosquitoe is d carrier
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Commander
what are pathogens
Don Reply
In biology, a pathogen (Greek: πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term pathogen came into use in the 1880s.[1][2
Zainab
A virus
Commander
Definition of respiration
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respiration is the process in which we breath in oxygen and breath out carbon dioxide
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how are lungs work
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in the mouth
EZEKIEL
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stimulates the follicle to release the mature ovum into the oviduct
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endocrine secrete hormone and regulate body process
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Biology is the study of living organisms, divided into many specialized field that cover their morphology, physiology,anatomy, behaviour,origin and distribution.
Lisah
biology is the study of life.
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Biology is the study of how living organisms live and survive in a specific environment
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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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