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DickBaldwinsays…Idon'tknowofanyemployerwhowantstheirprogrammerstospendtimeanddollarsreinventingtheclassicaldatastructures.Whatthoseemployersarelookingforisastaffofprogrammerswhounderstandthetradeoffsamongthedatastructures,andwhenitisappropriatetouseeachofthedifferentstructures.ItistimetoreinventthecurriculuminCS2coursesby•  Encouragingtheunderstandingoftechniquesforsoftware

reuse.•  Teachingwhen,why,andhoweachofthedifferent

structuresshouldbeused.•  Discouragingthereinventionofthosestructures.

CollectionACollectionrepresentsagroupofobjectsknownasitselementsBasicoperations:intsize(),booleanisEmpty(),booleancontains(Objectelement),booleanadd(Eelement),booleanremove(Objectelement),andIteratoriterator().Methodsthatoperateonentirecollections:containsAll(Collectionc),booleanaddAll(Collectionc),booleanretainAll(Collectionc),andvoidclear().Arrayoperations(suchasObject[]toArray()andT[]toArray(T[]a)InJDK8andlater,theCollectioninterfacealsoexposesmethodsStreamstream()andStreamparallelStream(),forobtainingsequentialorparallelstreamsfromtheunderlyingcollection.

ConvertingamongcollectionsByconventionallgeneral-purposecollectionimplementationshaveaconstructorthattakesaCollectionargument.Thisconstructor,knownasaconversionconstructor,initializesthenewcollectiontocontainalloftheelementsinthespecifiedcollection,whateverthegivencollection'ssubinterfaceorimplementationtype.Inotherwords,itallowsyoutoconvertthecollection'stype.Suppose,forexample,thatyouhaveaCollectionc,whichmaybeaList,aSet,oranotherkindofCollection.ThisidiomcreatesanewArrayList(animplementationoftheListinterface),initiallycontainingalltheelementsinc.Listlist=newArrayList(c);JDK7orlater:Listlist=newArrayList(c);

CollectionsutilitiesSTATICmethodsofclassCollections:•  disjoint(Collectionuno,Collectiondue)•  sort(List..)•  shuffle(Lista)•  min(Collectionuno,…)•  max(Collectionuno,…)•  frequency(Collectionuno,Objecto)•  binarySearch(List…)

Collections:interfacesvsimplementation

Interfaces

Set a Collection that cannot contain duplicate elements. It models the mathematical set abstraction.

SortedSet Set that maintains its elements in ascending order, sorted

according to the elements' \ordering or according to a Comparator

List an ordered Collection Queue

Deque

Map HashMap

SortedMap

TheListInterfaceAListisanorderedCollection).Listsmaycontainduplicateelements.Itincludesoperationsforthefollowing:•  Positionalaccess—manipulateselementsbasedontheirnumerical

positioninthelist.Thisincludesmethodssuchasget,set,add,addAll,andremove.

•  Search—searchesforaspecifiedobjectinthelistandreturnsitsnumericalposition.SearchmethodsincludeindexOfandlastIndexOf.

•  Iteration—extendsIteratorsemanticstotakeadvantageofthelist'ssequentialnature.ThelistIteratormethodsprovidethisbehavior.

•  Range-view—Thesublistmethodperformsarbitraryrangeoperationsonthelist.

TheSet

ASetisaCollectionthatcannotcontainduplicateelements.Itmodelsthemathematicalsetabstraction.

TheSet/SortedSetInterfaceASetthamaintainsitselementsinascendingorder,sortedaccordingtotheelements'naturalorderingoraccordingtoaComparatorprovidedatSortedSetcreationtime.InadditiontothenormalSetoperations,theSortedSetinterfaceprovidesoperationsforthefollowing:•  Rangeview—allowsarbitraryrangeoperationsonthesortedset•  Endpoints—returnsthefirstorlastelementinthesortedset•  Comparatoraccess—returnstheComparator,ifany,usedtosorttheset

publicinterfaceSortedSetextendsSet{//Range-viewSortedSetsubSet(EfromElement,EtoElement);SortedSetheadSet(EtoElement);SortedSettailSet(EfromElement);

//EndpointsEfirst();Elast();//ComparatoraccessComparator

QueueinterfaceAQueueisacollectionforholdingelementsinorderofarrival.BesidesbasicCollectionoperations,queuesprovideadditionalinsertion,removal,andinspectionoperations.TheQueueinterfacefollows.publicinterfaceQueueextendsCollection{Eelement();booleanoffer(Ee);Epeek();Epoll();Eremove();}

Dequeinterface

Adouble-ended-queueisalinearcollectionofelementsthatsupportstheinsertionandremovalofelementsatbothendpoints.

Type of Operation First Element (Beginning

of the Deque instance) Last Element (End of

the Deque instance)

Insert addFirst(e) addLast(e)offerFirst(e) offerLast(e)

Remove removeFirst() removeLast()pollFirst() pollLast()

Examine getFirst() getLast()peekFirst() peekLast()

MapinterfaceAMapisanobjectthatmapskeystovalues.Amapcannotcontainduplicatekeys:Eachkeycanmaptoatmostonevalue.Itmodelsthemathematicalfunctionabstraction.TheMapinterfaceincludesmethodsfor•  basicoperations(e.g.put,get,remove,containsKey,containsValue,size,andempty),

•  bulkoperations(e.g.putAllandclear),•  collectionviews(e.g.keySet,values).

SortedMapinterface

ASortedMapisaMapthatmaintainsitsentriesinascendingorder,sortedaccordingtothekeys'naturalordering,oraccordingtoaComparatorprovidedatthetimeoftheSortedMapcreation.

Collections:interfacesvsimplementation

Interfaces Hash table Implementations Resizable array

Implem. Tree

Implem. Linked list

Implem. Hash table + Linked

list Implem.

Set HashSet TreeSet LinkedHashSet

List ArrayList LinkedList

Queue ArrayDeque LinkedList

Deque ArrayDeque LinkedList

Map HashMap TreeMap LinkedHashMap

Set/SortedSetimplementationsHashSetismuchfasterthanTreeSet(constant-timeversuslog-timeformostoperations)butoffersnoorderingguarantees.IfyouneedtousetheoperationsintheSortedSetinterface,orifvalue-orderediterationisrequired,useTreeSet;otherwise,useHashSet.You'llendupusingHashSetmostofthetime.LinkedHashSetisin“intermediate”betweenHashSetandTreeSet.Implementedasahashtablewithalinkedlistrunningthroughit,itprovidesinsertion-orderediteration(leastrecentlyinsertedtomostrecently)andrunsnearlyasfastasHashSet.

ListimplementationsTherearetwogeneral-purposeListimplementations—ArrayListandLinkedList.Positionalaccessrequireslinear-timeinaLinkedListandconstant-timeinanArrayList.IfyoufrequentlyaddelementstothebeginningoftheListoriterateovertheListtodeleteelementsfromitsinterior,youshouldconsiderusingLinkedList.Theseoperationsrequireconstant-timeinaLinkedListandlinear-timeinanArrayList.Mostofthetime,you'llprobablyuseArrayList.

MapimplementationsHashMap,TreeMap,LinkedHashMap.IfyouneedSortedMapoperationsorkey-orderedCollection-viewiteration,useTreeMap.Iifyouwantmaximumspeedanddon'tcareaboutiterationorder,useHashMap.ifyouwantnear-HashMapperformanceandinsertion-orderiteration,useLinkedHashMap.Inthisrespect,thesituationforMapisanalogoustoSet.

Queue– Dequeueimplementations

LinkedList,plusmanyothers.

Suggerimento

•  NonscrivereMAIlabusinesslogicnelmain!

Anexampleimportjava.util.TreeSet;importjava.util.Collection;importjava.util.Iterator;publicclassAP400{publicstaticvoidmain(Stringargs[]){newWorker().doIt();}}

classWorker{publicvoiddoIt(){Collectionref=newTreeSet();Populator.fillIt(ref);Iteratoriter=ref.iterator();while(iter.hasNext()){System.out.print(iter.next());}System.out.println();}}

Anexample–part2classPopulator{publicstaticvoidfillIt(Collectionref){ref.add(newInteger(4));ref.add(newInteger(4));ref.add(newInteger(3));ref.add(newInteger(2));ref.add(newInteger(1));}}

Vedianchehttps://cnx.org/contents/dzOvxPFw@10.2:BaPSYll8@6/Java4010-Getting-Started-with-

SynchronizationThesynchronizationwrappersaddautomaticsynchronization(thread-safety)toanarbitrarycollection.Eachofthecorecollectioninterfaceshasonestaticfactorymethod.publicstaticCollectionsynchronizedCollection(Collectionc);publicstaticSetsynchronizedSet(Sets);publicstaticListsynchronizedList(Listlist);publicstaticMapsynchronizedMap(Mapm);publicstaticSortedSetsynchronizedSortedSet(SortedSets);publicstaticSortedMapsynchronizedSortedMap(SortedMapm);

SynchronizationwrappersCollectionmyCollection=newLinkedList;Collectionc=Collections.synchronizedCollection(myCollection);synchronized(c){for(Typee:c)foo(e);}

CollectionsandStreams

Seehttps://docs.oracle.com/javase/tutorial/collections/streams/index.html

I/O

TypicalJavaI/O… Scanner s = null;

try { s = new Scanner(

new BufferedReader( new FileReader("xanadu.txt”)));

while (s.hasNext()) { System.out.println(s.next()); } } finally { if (s != null) { s.close(); } }

Bydefault,ascanneruseswhitespacetoseparatetokens.Whitespacecharactersincludeblanks,tabs,andlineterminators.

https://docs.oracle.com/javase/tutorial/essential/io/scanning.html

I/OTable  Byte Based Character Based

  Input Output Input Output

Basic InputStream OutputStreamReader Writer

InputStreamReader OutputStreamWriter

Arrays ByteArrayInputStream ByteArrayOutputStream CharArrayReader CharArrayWriter

FilesFileInputStream FileOutputStream

FileReader FileWriterRandomAccessFile RandomAccessFile

Pipes PipedInputStream PipedOutputStream PipedReader PipedWriter

Buffering BufferedInputStream BufferedOutputStream BufferedReader BufferedWriter

Filtering FilterInputStream FilterOutputStream FilterReader FilterWriter

ParsingPushbackInputStream PushbackReader

 StreamTokenizer LineNumberReader

Strings StringReader StringWriter

Data DataInputStream DataOutputStream

Data - Formatted PrintStream PrintWriter

Objects ObjectInputStream ObjectOutputStream  

Utilities SequenceInputStream      

ReadingfromfilePathfile=...;try(InputStreamin=Files.newInputStream(file);BufferedReaderreader=newBufferedReader(newInputStreamReader(in))){Stringline=null;while((line=reader.readLine())!=null){System.out.println(line);}}catch(IOExceptionx){System.err.println(x);}

Toopenafileforreading,youcanusethenewInputStream(Path,OpenOption...)method.Thismethodreturnsanunbufferedinputstreamforreadingbytesfromthefile

Writingtofileimportstaticjava.nio.file.StandardOpenOption.*;importjava.nio.file.*;importjava.io.*;publicclassLogFileTest{publicstaticvoidmain(String[]args){//Convertthestringtoabytearray.Strings="HelloWorld!";bytedata[]=s.getBytes();Pathp=Paths.get("./logfile.txt");try(OutputStreamout=newBufferedOutputStream(Files.newOutputStream(p,CREATE,APPEND))){out.write(data,0,data.length);}catch(IOExceptionx){System.err.println(x);}}}

ThenewOutputStreammethodopensorcreatesafileforwritingbytesandreturnsanunbufferedoutputstream.

java.nio.file:fileproperties

Pathfile=...;booleanisRegularExecutableFile=Files.isRegularFile(file)&Files.isReadable(file)& Files.isExecutable(file);

FormattingpublicclassRoot2{publicstaticvoidmain(String[]args){inti=2;doubler=Math.sqrt(i);System.out.format("Thesquarerootof%dis%f.%n",i,r);}}Thesquarerootof2is1.414214.

publicclassFormat{publicstaticvoidmain(String[]args){System.out.format("%f,%1$+020.10f%n",Math.PI);}}3.141593,+00000003.1415926536

PathYoucaneasilycreateaPathobjectbyusingoneofthefollowinggetmethodsfromthePaths(notetheplural)helperclass:Pathp1=Paths.get("/tmp/foo");Pathp2=Paths.get(args[0]);Pathp3=Paths.get(URI.create("file:///Users/joe/FileTest.java"));Thiscreates/u/joe/logs/foo.logassumingyourhomedirectoryis/u/joe,orC:\joe\logs\foo.logifyouareonWindows.Pathp5=Paths.get(System.getProperty("user.home"),"logs","foo.log");

Watchingadirectoryforchange

https://docs.oracle.com/javase/tutorial/essential/io/notification.html

Seetutorial

•  https://docs.oracle.com/javase/tutorial/essential/io/index.html

Database

JDBCTutorial

https://docs.oracle.com/javase/tutorial/jdbc/overview/index.htmlhttps://docs.oracle.com/javase/tutorial/jdbc/basics/index.html

Concurrency

Concurrency

https://docs.oracle.com/javase/tutorial/essential/concurrency/index.html

IDEforJava

AccordingtoJavaWorld…ThreeIDEsarethemajorones:•  IntellijIDEA•  Eclipse•  Netbeans

https://www.javaworld.com/article/3114167/development-tools/choosing-your-java-ide.html

ItendtorecommendthatnewJavacodersnotuseEclipse.Eventhoughit'sthemostpopularJavaIDE,ithasthesteepestlearningcurveandthemostpotentialforconfusion,bothindailyuseandwhenmaintainingtheIDE.

FornewJavacoderswithoutabudgetfortools,thechoiceisbetweenNetBeansandIntelliJIDEACommunityEdition.Ifyou'recodingJavaserverswithlittleornobudgetfortools,thenNetBeansmightbethebetterchoice

BlueJVantaggi:IntegrazioneconUML!

Svantaggioprincipale:mancalaautocompletion

BlueJVantaggi:visualizzazioneimmediatadelladocumentazionegenerata

Svantaggi:noversioning,norefactoring,nointegratedservers…

Netbeansbasics

Handson:1)  Createproject2)  Codecompletion3)  Runproject–runfile4)  Rebuild

Netbeansimportantelements

1)  MaximizeWindow–ResetWindows2)  Projectproperties3)  Configuration

Netbeans–interestingfeatures1)  Sourceformat2)  Refactor3)  Codeinspection4)  Navigate5)  Findusages6)  Insertcode7)  debug