Data structures outside in with Java

512 Pages·2.93 MB·English

by  Venugopal, Sesh

DATA STRUCTURES OUTSIDE IN
™
With Java
Sesh Venugopal
Rutgers University
UpperSaddleRiver,NewJersey07458
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Venugopal,Sesh.
DataStructuresOutsideInwithJava/SeshVenugopal.
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ISBN0-13-198619-8
1.Datastructures(Computerscience)2.Java(Computerprogramlanguage)
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Preface
Therearetwobroadapproachestostudyingdatastructures.
Oneisthe‘‘inside-out’’approachinwhichtheimplementationofthedatastructure,
i.e.,howitisbuilt,islearnedeitherbeforeorinconjunctionwithitsapplicationtoproblem
solving.Inotherwords,startfromthenucleusofthedatastructureandbuildoutwardto
itsuseinaproblem.
Theinside-outapproach,however,isdiscordantwiththemannerinwhichsoftware
isbuiltinpracticeoutoflibrariesofobjectsthatareknownonlythroughtheirapplication
programming interfaces (APIs). Here, the ‘‘outside-in’’ approach becomes the norm: a
component orobjectisfirst—andoftenonly—seenviaits interface,whichcharacterizes
itsbehaviorandthereforeitssuitabilityforagivenapplication.Thatis,whatacomponent
doesprecedeshowitisbuilt.
Outside-in:Fromprice-taggedinterfacetoimplementation
In this book, we are interested in the interface as well as the implementation of data
structures. We follow the outside-in approach to presenting them because it will enable
students to easily apply in practical software development what they learn in class. Our
approachisoutlinedinthefollowingsequenceofsteps.
1. Introduceadatastructurebynarratingitspropertiesanduseinapplications.
This step familiarizes the student with the characteristic behavior of the data
structure,settingthestagefortheencapsulationofdataandoperationsintoaJava
class.
2. Formalizethecharacteristicpropertiesofadatastructurebypresentingthepublic
interfaceofaJavaclassthatimplementsthedatastructure.
This step defines the set of operations that may be applied on the data structure,
formulated from the discussion in Step 1. With the interface, there also comes a
‘‘pricetag’’—therunningtimesoftheinterfaceoperations.
Thepricetagisanimportantconsiderationintheselectionofdatastructuresforan
application. It may be argued that the price tag determination may only be made
afterthedatastructureisimplemented. Whilethisistrue,theoutside-inapproach
thatisusedtobuildsoftwareinpracticetypicallyseparatesthegroupofpeoplewho
work with the outside from the group of people who build the inside. The outside
group must rely on all, and only, that information that comes with the interface.
Havingapricetagwiththeinterfaceiscriticalfortheoutsidegrouptoevaluateand
choosethebestobjectspossiblefortheapplicationathand.
Tobeconsistentwiththisapproach,wehaveattachedthepricetagtotheinterface,
butmadeaworkingcompromise:intheinterface,specifytheminimalrequirements
of the implementation so that the running times of the operations stay within the
pricetag.
We admit that this blurs the separation between interface and implementation,
whilerecognizingthatpartoftheissueisalsothatthesameperson—thestudent—is
v
vi Preface
working with both the outside and the inside, albeit at different times. The best
wayforthestudenttoapproachtheinterface-implementation separationistofirst
imagine that he or she is a client of the data structure, with full cognizance of the
interface and the price tag, and then imagine being the implementor of the data
structure, who has been told whatlimitations (price tag) to work with to build the
structure.
3. Further illustrate the use of a data structure by writing Java applications using its
classinterfacepresentedinStep2.
This step gives the student a clear practical understanding of how to build an
application in Java using a data structure whose public interface is known, but
whoseinternalimplementationishidden.
Steps 2 and 3 strongly emphasize the interface of a data structure. By repeatedly
building applications using only thepublic interfaceofdata structures,the student
gets a practical feel for software development using components whose internal
implementationdetailsneednot(andindeed,maynot)beavailable.
4. Design and implement the data structure, i.e., develop the code for the Java class
whoseinterfacewaspresentedinStep2,analyzetherunningtimesofitsoperations,
andverifythemagainstthepricetag.
Thisstepemphasizescodereuseinoneoftwoforms:(a)composition:usingprevious
data structuresas component (Java)objects inbuilding, or composing, a new data
structure, or (b) inheritance: building a new data structure by inheriting from a
previouslybuiltdatastructure(Javaclass).
Whilewearefollowing anoutside-inapproach,this‘‘in’’partdoesnotdegenerate
into using classes from the Java collections framework. Instead, it is on an equal
footingwiththe‘‘outside’’part,withadetailedunderstandingoftheimplementation
sothatthestudentlearnsallaspectsofbuildingdatastructures,includingevaluating
thetradeoffsinvolvedinchoosingamongasetofcandidateimplementations.
Apart from providing a consistent pedagogical form, these steps help students to
understand and apply the important object-oriented design principles of encapsulation,
separationofinterfacefromimplementation,andcodereuse.
PrerequisitesinJava
This book assumes a CS1-level background in Java 1.5, with the following specific
coverage: program structure, data types, control structures for decision and repetition,
includingtheif,if-else,for,while,andrepeatstatements,andarrays.Italsoassumes
thatthestudentisfamiliarwiththewidelyusedStringclass.
Chapter 1 is a Java primer on object-oriented programming that starts by assum-
ing this CS1-level background, and introduces objects and classes, inheritance, the
Object class, exceptions, core input and output features, class packaging, and access
control. In the context of input/output, the java.util.StringTokenizer and the
java.util.Scanner (new to Java 1.5) classes are described, with a discussion of their
typicalusage.
Preface vii
Theprimeralsointroducesspecificallydesign-orientedfeatures,includingpolymor-
phism,abstractclasses,andinterfaces.
The last section discusses the new Java 1.5 generics, an indispensable tool for
buildingusableandrobustdatastructures.Thisdiscussionalsodetailsthedesignanduse
of the java.util.ArrayList class, which is a very useful component in implementing
containerstructures,orcollections.
Pathsthroughthebook
Anessentialcoursefocusingonthebasicdatastructuresandsortingalgorithms,preceded
by reviewing/learning the required Java tools and techniques in two weeks, could cover
Chapters1–10,skippingSection10.7(AVLTree),andChapters12–13,skippingSections
13.3(Heapsort)and13.4(Radixsort).
A course that could conduct the Java due diligence in lab instead of lecture could
add Heap from Chapter 11, and Heapsort and Radix sort from Sections 13.3 and 13.4
respectively.
AdvancedmaterialcouldbeincorporatedbycoveringAVLtreesfromSection10.7,
andChapters14and15ongraphs.Incaseoftimelimitation,Chapter14wouldsufficeto
familiarizestudentswithgraphalgorithms,whileleavingouttheimplementation details
ofChapter15.
A two-course sequence could cover the entire book, including much of the Java
backgroundmaterialinChapter1.ThefirstcoursecouldcoverChapters1through9,up
to and including Binary Tree/General Tree, and the second could cover the rest of the
chapters,startingwithBinarySearchTree/AVLTreeofChapter10.
Pedagogicalstructures.
• Every chapter, except the preliminary Chapters 1 and 2, begins with a list of
Learning Objectives.Thisgivesapreciseoverviewofthelearningmaterialinthe
chapter.
• Keypointsineverychapterarepresentedinthefollowingformat:
Thesekeypointsarealsoitemizedintheend-of-chaptersummary.
• Public interfaces of Java classes for data structures are presented as figures in the
followingformat:
Class classname
Constructors
Signatureanddescriptionofeachpublicconstructor
Methods
Runningtime(pricetag),signature,anddescriptionofeachpublicmethod
viii Preface
• EverycompleteJavaclassimplementationispresentedinthefollowingstyle:
ClassFilenumber ClassFileName
Classoutline,withsomeconstructors/methodspossiblyfilledin
• Throughoutthebook,weusealgorithmswritteninpseudo-code,providinglanguage-
independent descriptions of processes. These algorithms appear with a header of
theform:
Algorithm name of algorithm
Thenotationsusedinthepseudo-codeareself-explanatory.
• EverychapterexceptChapter2concludeswithalistingofSummarypoints.These
includethekeypointsinthechapter,aswellasotherimportantpointstoremember,
includingspecificJavaissues.
• EverychapterexceptChapter2teststhestudent’sunderstandingofthematerialin
theformofexercisesandprogrammingproblems:
• Exercises, which are, for the most part, conceptual language-independent
material, especiallyfocusingonwork-through reviews,abstractdesignissues,
andtime-spaceanalysis.
• ProgrammingProblems,whichfocusonbuildingJavaclasses,especiallyfocus-
ingondesign/implementationalternativesandcodereuse.
Acknowledgments
IwouldliketothanktheDataStructuresteamsintheComputerSciencedepartmentat
Rutgers University with whom I have taught this course for over more than a decade,
and who have provided direct as well as indirect input that has helped shape this book.
Special thanks to current and former faculty members Diane Souvaine, Ken Kaplan,
MilesMurdocca,andDonSmithfordiscussingandreviewingthecontent.
Many thanks to my friends and former graduate student colleagues Nathalie
Japkowicz,GeorgeKatsaros,andDanArenaforcarefullyreviewingtheinitialC++draft,
Gabriela Hristescu for providing help with typesetting aspects, and Sri Divakaran for
reviewing parts of the Java manuscript. Several students in my data structures class of
Fall 1997 readthe firstcomplete draft of this book and gave valuable feedback. Thanks
tothemall,especiallyAlexChang,forbeingsuchatremendouslyloyalfanofthebook.
ThanksalsotothestudentsinFall2002andSpring2003whopointedoutvariouserrors
andothershortcomingsinanearlierversionthatwascustomizedforRutgers.
Thanks are also due to the Data Structures faculty at Middlesex County College,
and my former colleagues when I was working at Lucent Technologies with whom I
discussed the material in this book at some point or the other. Special thanks to Tom
WalshatLucentforcheeringmeon.
Thankstoallthereviewerswhohelpedmakethisabetterbook:BarbaraGoldner
at North Seattle Community College, Mark Llewellyn at University of Central Florida,
ChrisDovolisatUniversityofMinnesota,IyadA.AjwaatAshlandUniversity,Minseok
Kwon at Rochester Institute of Technology, George Rouskas at North Carolina State
Preface ix
University, Roxanne Canosa at Rochester Institute of Technology, Mary Horstman at
WesternIllinoisUniversity,RayWhitneyatUniversityofMaryland,UniversityCollege,
andRobertP.BurtonatBrighamYoungUniversity.
TheeditorialteamatPrenticeHallhavesupportedmeinallaspectsofthisproject.
Thanks to my editor Tracy Dunkelberger for believing that this book project would be
a worthwhile enterprise, for her cheery confidence that kept me on an even keel, and
formakingthisbookreal.ThankstoChristiannaLeeandCaroleSnyderforguidingme
through the review process, and for responding to all my questions with patience and
grace.
John Shannon, Irwin Zucker, Camille Trentacoste and the production staff at
Laserwordshelpedcorrectthenumeroustypographicalandgrammaticalerrorsthathad
crept into the book, and formatted the pages to make sure they were presentable. Due
totheirdiligenceandexpertise,you,dearreader,aresparedmyinadvertentmistakesor
plainignoranceintheseareas.Forthis,mysincereappreciationandthankstoallofthem.
I am deeply grateful to the members of my family and that of my wife’s for their
adviceandencouragement,andforbeingtheretopepmeupwhenthingsdidn’tseemto
begoingtoowellattimes.Iwouldspeciallyliketothankmyparents,mymother-in-law,
and my wife’s grandparents for their constant support. Above all, thanks to my father,
C.N. Venugopal, and to my wife’s grandfather, Dr. Hayrettin Tanacan, for their special
participation. Although both of them are far removed from computers in general, and
Data Structures in particular, they took the pains to go through my book to try and
understandexactlywhatitwasthatIwastryingtowritethatwastakingsolong!
Thankstomywife,ZehraTulin,forherhelpinmanywaysduringthewritingofthis
book,andmoreimportantly,forherloveandsupportatalltimes.Andanextrabighug
tomysonAmarwhoseunfailingprideinhisdadspursmeon.
Finally,thankstoallthestudentswhotookmyclassesinvarioussubjectsatRutgers
University and Middlesex County College over the years. They have been instrumental
inmygrowthasaneducator,andIhopethisbookcanserveasatokenofmygratitudeto
eachandeveryoneofthem.
Inclosing,Iwouldbeveryhappytohearfromyouaboutthisbook—whatyouliked,
whatyoudidnotcarefor,andtheerrorsyoufound,ifany.Youcanreachmebyemailat
sesh [email protected].
SeshVenugopal
Piscataway,NewJersey
November,2006