Principles of Software Construction: Objects, Design, and Concurrency...

1 17-214

PrinciplesofSoftwareConstruction: Objects,Design,andConcurrencyPart2:DesigncasestudiesDesigncasestudy:JavaCollectionsCharlieGarrodChrisTimperley

2 17-214

Administrivia

•  Homework4bduenextThursday,October17th•  Homework4afeedbackavailable

–  Canregainupto75%oflostHomework4acredit•  DirectlyaddressTAcommentswhenyouturninHomework4c•  Turninreviseddesigndocuments+scansofourfeedback+descriptionofwhatyouchanged

https://commons.wikimedia.org/wiki/File:1_carcassonne_aerial_2016.jpg

3 17-214

KeyconceptsfromTuesday

4 17-214

KeyconceptsfromTuesday

•  GUIsarefilledwithdesignpatterns–  Strategy–  Templatemethod–  Observer–  Composite–  Decorator–  Adapter–  Façade–  Command–  Chainofresponsibility

5 17-214

Today:JavaCollections

Source: http://wiki3.cosc.canterbury.ac.nz/index.php/User:Jenny_Harlow/Design_study/Java_Collections_Framework

6 17-214

Learninggoalsfortoday

•  Understandthedesignchallengesofcollectionlibraries.•  Recognizethedesignpatternsusedandhowthosedesign

patternsachievedesigngoals.–  Markerinterface–  Decorator–  Factorymethod–  Iterator–  Strategy–  Templatemethod–  Adapter

7 17-214

Designingadatastructurelibrary

•  Differentdatatypes:lists,sets,maps,stacks,queues,…•  Differentrepresentations

–  Array-basedlistsvs.linkedlists–  Hash-basedsetsvs.tree-basedsets–  …

•  Manyalternativedesigndecisions–  Mutablevs.immutable–  Sortedvs.unsorted–  Primitivedatavs.objects–  Acceptsnullornot–  Acceptsduplicatesornot–  Concurrency/thread-safeornot–  …

8 17-214

ThephilosophyoftheCollectionsframework

•  Powerfulandgeneral•  Smallinsizeandconceptualweight

–  Mustfeelfamiliar–  Onlyincludefundamentaloperations–  "Funandeasytolearnanduse"

9 17-214

OverviewoftheCollectionsframework

•  Coreinterfaces•  General-purposeimplementations•  Wrapperandspecial-purposeimplementations•  Abstractimplementationsforeasyreuse•  Separatealgorithmslibrary

10 17-214

Example:Howtofindanagrams

•  Alphabetizethecharactersineachword–  cat→act,dog→dgo,mouse→emosu–  Resultingstringiscalledalphagram

•  Anagramssharethesamealphagram!–  stop→opst,post→opst,tops→opst,opts→opst

•  Sogothroughwordlistmaking“multimap”fromalphagramtoword!

11 17-214

HowtofindanagramsinJava(1)

publicstaticvoidmain(String[]args)throwsIOException{//ReadwordsfromfileandputintoasimulatedmultimapMap<String,List<String>>groups=newHashMap<>();try(Scanners=newScanner(newFile(args[0]))){while(s.hasNext()){Stringword=s.next();Stringalpha=alphabetize(word);List<String>group=groups.get(alpha);if(group==null)groups.put(alpha,group=newArrayList<>());group.add(word);}}

12 17-214

HowtofindanagramsinJava(2)

//PrintallanagramgroupsabovesizethresholdintminGroupSize=Integer.parseInt(args[1]);for(List<String>group:groups.values())if(group.size()>=minGroupSize)System.out.println(group.size()+":"+group);}//ReturnsthealphagramforastringprivatestaticStringalphabetize(Strings){char[]a=s.toCharArray();Arrays.sort(a);returnnewString(a);}

13 17-214

TwoslidesinJavavs.achapterinSTLJava’sverbosityissomewhatexaggerated

14 17-214

TheCollectioninterface

publicinterfaceCollection<E>{intsize();booleanisEmpty();booleancontains(Objectelement);booleanadd(Eelement);//Optionalbooleanremove(Objectelement);//OptionalIterator<E>iterator();Object[]toArray();T[]toArray(Ta[]);//BulkoperationsbooleancontainsAll(Collection<?>c);booleanaddAll(Collection<?extendsE>c);//OptionalbooleanremoveAll(Collection<?>c);//OptionalbooleanretainAll(Collection<?>c);//Optionalvoidclear();//Optional…}

14

15 17-214

TheListinterface:anorderedcollection

publicinterfaceList<E>extendsCollection<E>{Eget(intindex);Eset(intindex,Eelement);//Optionalvoidadd(intindex,Eelement);//OptionalObjectremove(intindex);//OptionalbooleanaddAll(intindex,Collection<?extendsE>c);//OptionalintindexOf(Objecto);intlastIndexOf(Objecto);List<E>subList(intfrom,intto);ListIterator<E>listIterator();ListIterator<E>listIterator(intindex);}

16 17-214

TheSetinterface:collectionofdistinctitems

•  Addsnomethods!•  Specificationrequiresnoduplicateitemsincollection•  Themarkerinterfacedesignpattern

–  Markerinterfacesaddinvariants,nocode

publicinterfaceSet<E>extendsCollection<E>{}

17 17-214

TheMapinterface:key-valuemapping

publicinterfaceMap<K,V>{intsize();booleanisEmpty();booleancontainsKey(Objectkey);booleancontainsValue(Objectvalue);Objectget(Objectkey);Objectput(Kkey,Vvalue);//OptionalObjectremove(Objectkey);//OptionalvoidputAll(Map<?extendsK,?extendsV>t);//Opt.voidclear();//Optional//CollectionviewspublicSet<K>keySet();publicCollection<V>values();publicSet<Map.Entry<K,V>>entrySet();}

18 17-214

RecalltheIteratorinterface

publicinterfaceIterator<E>{booleanhasNext();Enext();voidremove();//Optional}

19 17-214

Aside:Thefactorymethodpattern

publicinterfaceCollection<E>{intsize();booleanisEmpty();booleancontains(Objectelement);booleanadd(Eelement);//Optionalbooleanremove(Objectelement);//OptionalIterator<E>iterator();Object[]toArray();T[]toArray(Ta[]);//BulkoperationsbooleancontainsAll(Collection<?>c);booleanaddAll(Collection<?extendsE>c);//OptionalbooleanremoveAll(Collection<?>c);//OptionalbooleanretainAll(Collection<?>c);//Optionalvoidclear();//Optional…}

19

Definesaninterfaceforcreatinganiterator,butallowscollectionimplementationtodecidewhichiteratortocreate.

20 17-214

Thefactorymethoddesignpattern

•  Problem:Subclassesneedtocontrolthetypeofobjectcreated•  Solution:Defineanmethodthatconstructstheobject;

subclassescanoverridethemethod.•  Consequences:

–  Namescanbemeaningful,self-documenting–  Canavoidconstructinganewobject–  Mightbehardtodistinguishfactorymethodfromothermethods

21 17-214

Otherfactorymethodexamples

•  Fromjava.util.Collections:List<T>emptyList();Set<T>emptySet();Map<K,V>emptyMap();Set<T>singleton(Titem);List<T>singletonList(Titem);List<T>nCopies(intn,Titem);

22 17-214

Interface ImplementationSet HashSetList ArrayListQueue ArrayDequeDeque ArrayDeque[stack] ArrayDequeMap HashMap

General-purposeimplementations

23 17-214

General-purposeimplementations(continued)

Interface Implementation(s)List LinkedListSet LinkedHashSet

TreeSetEnumSet

Queue PriorityQueueMap LinkedHashMap

TreeMapEnumMap

24 17-214

Wrapperandspecial-purposeimplementations

•  Unmodifiablecollections(fromjava.util.Collections):Collection<T>unmodifiableCollection(Collection<?extendsT>c);List<T>unmodifiableList(List<?extendsT>list);Map<K,V>unmodifiableMap(Map<?extendsK,?extendsV>m);

25 17-214



•  Synchronizedcollections(fromjava.util.Collections):Collection<T>synchronizedCollection(Collection<?extendsT>c);List<T>synchronizedList(List<?extendsT>list);Map<K,V>synchronizedMap(Map<?extendsK,?extendsV>m);

26 17-214



•  Synchronizedcollections(fromjava.util.Collections):Collection<T>synchronizedCollection(Collection<?extendsT>c);List<T>synchronizedList(List<?extendsT>list);Map<K,V>synchronizedMap(Map<?extendsK,?extendsV>m);

•  AListbackedfromanarray(fromjava.util.Arrays):List<T>asList(T…a);

Theadapterpattern:ReturnsaspecializedlistimplementationthatadaptsthearrayAPItothejava.util.ListAPI

27 17-214

e.g.,TheUnmodifiableCollectionclass

publicstatic<T>Collection<T>unmodifiableCollection(Collection<T>c){returnnewUnmodifiableCollection<>(c);

}classUnmodifiableCollection<E>

implementsCollection<E>,Serializable{

finalCollection<E>c;

UnmodifiableCollection(Collection<>c){this.c=c;}publicint size() {returnc.size();}publicbooleanisEmpty() {returnc.isEmpty();}publicbooleancontains(Objecto){returnc.contains(o);}publicObject[]toArray() {returnc.toArray();}public<T>T[]toArray(T[]a) {returnc.toArray(a);}publicString toString() {returnc.toString();}publicbooleanadd(Ee){thrownewUnsupportedOperationException();}publicbooleanremove(Objecto) {thrownewUnsupportedOperationException();}publicbooleancontainsAll(Collection<?>coll){returnc.containsAll(coll);}publicbooleanaddAll(Collection<?extendsE>coll){thrownewUnsupportedOperationException();}publicbooleanremoveAll(Collection<?>coll){thrownewUnsupportedOperationException();}publicbooleanretainAll(Collection<?>coll){thrownewUnsupportedOperationException();}publicvoidclear(){thrownewUnsupportedOperationException();}

}

28 17-214




implementsCollection<E>,Serializable{

finalCollection<E>c;


}

What design pattern is this?

29 17-214




implementsCollection<E>,Serializable{finalCollection<E>c;


}


UnmodifiableCollection decorates Collection by removing functionality…

30 17-214

Abstractimplementationsforeasyreuse

publicabstractAbstractList<E>extendsAbstractCollection<E>implementsList<E>{abstractpublicintsize();abstractpublicEget(intindex);publicbooleanisEmpty(){returnsize()==0;}publicbooleancontains(Objectelement){for(inti=0;i<size();i++){if(get(i).equals(element)){returntrue;}}returnfalse;}publicbooleanadd(intindex,Eelement){thrownewUnsupportedOperationException();}publicbooleanremove(intindex){thrownewUnsupportedOperationException();}…}

31 17-214

Implementinganewlisttype

/***Returnsanunmodifiableviewofthegivenlist,equivalentto*thereverseofthegivenlist.Thereturnvalueisbacked*bytheoriginallist,usingO(1)additionalspace.*/publicstatic<T>List<T>reverseOf(List<T>list){...}

32 17-214

Implementinganewlisttype

/***Returnsanunmodifiableviewofthegivenlist,equivalentto*thereverseofthegivenlist.Thereturnvalueisbacked*bytheoriginallist,usingO(1)additionalspace.*/publicstatic<T>List<T>reverseOf(List<T>list){returnnewAbstractList<T>(){

@Overridepublicintsize(){returnlist.size();}@OverridepublicTget(intindex){returnlist.get(size()–index–1)}};}

33 17-214


publicabstractAbstractList<E>extendsAbstractCollection<E>implementsList<E>{abstractpublicintsize();abstractpublicEget(intindex);publicbooleanisEmpty(){returnsize()==0;}publicbooleancontains(Objectelement){…}publicbooleanadd(intindex,Eelement){thrownewUnsupportedOperationException();}publicbooleanremove(intindex){thrownewUnsupportedOperationException();}…}


34 17-214


publicabstractAbstractList<E>extendsAbstractCollection<E>implementsList<E>{abstractpublicintsize();abstractpublicEget(intindex);publicbooleanisEmpty(){returnsize()==0;}publicbooleancontains(Objectelement){…}publicbooleanadd(intindex,Eelement){thrownewUnsupportedOperationException();}publicbooleanremove(intindex){thrownewUnsupportedOperationException();}…}


The template method design pattern: size and get are primitive operations, other methods are template methods.

35 17-214

35

Reusablealgorithmsinjava.util.Collections

static<TextendsComparable<?superT>>voidsort(List<T>list);

staticintbinarySearch(Listlist,Objectkey);

static<TextendsComparable<?superT>>Tmin(Collection<T>coll);

static<TextendsComparable<?superT>>Tmax(Collection<T>coll);

static<E>voidfill(List<E>list,Ee);

static<E>voidcopy(List<E>dest,List<?ExtendsE>src);

staticvoidreverse(List<?>list);

staticvoidshuffle(List<?>list);

36 17-214

e.g.sortingaCollection

•  UsingCollections.sort:publicstaticvoidmain(String[]args){List<String>list=Arrays.asList(args);Collections.sort(list);for(Strings:list){System.out.println(s);}}

37 17-214

Sortingyourowntypesofobjects

publicinterfaceComparable<T>{intcompareTo(To);}•  Generalcontracts:

–  a.compareTo(b)shouldreturn:<0 ifaislessthanb

0 ifaandbareequal>0 ifaisgreaterthanb

–  Shoulddefineatotalorder:•  Ifa.compareTo(b)<0andb.compareTo(c)<0,thena.compareTo(c)shouldbe<0

•  Ifa.compareTo(b)<0,thenb.compareTo(a)shouldbe>0–  Shouldusuallybeconsistentwith.equals:

•  a.compareTo(b)==0iffa.equals(b)

38 17-214

Comparableobjects–anexample

publicclassIntegerimplementsComparable<Integer>{privatefinalintval;publicInteger(intval){this.val=val;}…publicintcompareTo(Integero){if(val<o.val)return-1;if(val==o.val)return0;return1;}}

39 17-214

Comparableobjects–anotherexample

•  Make Name comparable: publicclassName{privatefinalStringfirst,last;publicName(Stringfirst,Stringlast){if(first==null||last==null)thrownewNullPointerException();this.first=first;this.last=last;}…

}•  Hint:StringsimplementComparable<String>

40 17-214

Comparableobjects–anotherexample

•  Make Name comparable: publicclassNameimplementsComparable<Name>{privatefinalStringfirst,last;publicName(Stringfirst,Stringlast){if(first==null||last==null)thrownewNullPointerException();this.first=first;this.last=last;}publicintcompareTo(Nameo){intlastComparison=last.compareTo(o.last);if(lastComparison!=0)returnlastComparison;returnfirst.compareTo(o.first);}

} Hint:StringsimplementComparable<String>

41 17-214

Alternativecomparisons

publicclassEmployeeimplementsComparable<Employee>{protectedNamename;protectedintsalary;…}•  WhatifwewanttosortEmployeesbyname,usually,but

sometimessortbysalary?

42 17-214

Alternativecomparisons

publicclassEmployeeimplementsComparable<Employee>{protectedNamename;protectedintsalary;…}•  WhatifwewanttosortEmployeesbyname,usually,but

sometimessortbysalary?•  Answer:There'saStrategypatterninterfaceforthat:publicinterfaceComparator<T>{publicintcompare(To1,To2);}

43 17-214

WritingaComparatorobjectpublicclassEmployeeimplementsComparable<Employee>{protectedNamename;protectedintsalary;publicintcompareTo(Employeeo){returnname.compareTo(o.name);}}publicclassSalaryComparatorimplementsComparator<Employee>{publicintcompare(Employeeo1,Employeeo2){returno1.salary–o2.salary;}}

44 17-214

Summary

•  Collectionsasreusableandextensibledatastructures–  designforreuse–  designforchange

•  Iteratorstoabstractoverinternalstructure•  Decoratortoattachbehavioratruntime•  Templatemethodsandfactorymethodstosupport

customizationinsubclasses•  Adapterstoconvertbetweenimplementations•  Strategypatternforsorting

Principles of Software Construction: Objects, Design, and Concurrency...

Documents

Transcript of Principles of Software Construction: Objects, Design, and Concurrency...