Eclipse Collec+ons and Java 8 Lambdas · • java.util.Collections provides methods for sort(), min(), max() and just a few others. • The most common iteraon paerns are missing:

EclipseCollec+onsandJava8Lambdas

MiniCodeKataBasicIdeas,BasicImplementa+onsMarch2016

Copyright©2016GoldmanSachs.Allrightsreserved.

INTRO

WhatisEclipseCollec+ons?

• AsupplementorreplacementfortheJavaCollecFonsFramework(JCF).• DevelopedoriginallyatGoldmanSachs.• "Inspiredby"SmalltalkCollecFonprotocol.

2

WhatisaCodeKata?

• AprogrammingexercisewhichhelpshoneyourskillsthroughpracFce.• Thisoneissetupasaseriesofunittestswhichfail.• Yourtaskistomakethempass,usingEclipseCollecFons–

IhearandIforget.IseeandIremember.IdoandIunderstand.

-Confucius

EclipseCollec+onsMiniCodeKata

• Newconceptsareintroducedintheslides• CodingexercisesareattheendofeachsecFon.

ITERATIONPATTERNS

3

ITERATIONP

ATTERNS

Sort

• WhatisaniteraFonpaWern?• Sortisoneexample.• Wewanttosortalistofpeoplebylastname,firstname.• WhichmethodintheJCFcanweuse?

Domain

Personjohn=newPerson("John","Smith");Personjane=newPerson("Jane","Smith");Personz=newPerson("Z.","Jones");List<Person>people=newArrayList<Person>();people.add(john);people.add(jane);people.add(z);

4

ITERATIONP

ATTERNS

Javadoc

publicstaticvoidjava.util.Collections.sort(List<T>list,Comparator<?superT>c)

Sortsthespecifiedlistaccordingtotheorderinducedbythespecifiedcomparator.Allelementsinthelistmustbemutuallycomparable.

Anonymousinnerclasssyntax

Collections.sort(people,newComparator<Person>(){publicintcompare(Persono1,Persono2){intlastName=o1.getLastName().compareTo(o2.getLastName());if(lastName!=0){returnlastName;}returno1.getFirstName().compareTo(o2.getFirstName());}});

5

ITERATIONP

ATTERNS

Javadoc



DoesanythingbotheryouaboutCollections.sort()?

6

ITERATIONP

ATTERNS

Javadoc




JCFproblems

• Whyisn’tsort()amethodoneveryList?Collections.sort(list,comparator);

vs.list.sort(comparator);

7

ITERATIONP

ATTERNS

Javadoc




JCFproblems

• WherearealltheiteraFonpaWerns?• java.util.Collectionsprovidesmethodsforsort(),min(),max()andjustafewothers.

• ThemostcommoniteraFonpaWernsaremissing:• Collectalistofeachperson’sfirstname.• Selectonlythosepeoplewhoselastnameis“Smith”.

8

ITERATIONP

ATTERNS

Itera+onPaLerns

• Wewantthemethodssort(),min(),max(),collect(),select(),etc.oneverycollecFon.

• Howcanweaccomplishthisincode?• CreateinterfacesthatextendtheJCFinterfaces.

EclipseCollec+onsInterfaces

publicinterfaceMutableList<T>extendsList<T>{MutableList<T>sortThis(Comparator<?superT>comparator);<V>MutableList<V>collect(Function<?superT,?extendsV>function);

MutableList<T>select(Predicate<?superT>predicate);...}

9

COLLECTP

ATTERNItera+onPaLern

• CollectpaWern(akamaportransform).• ReturnsanewcollecFonwhereeachelementhasbeentransformed

• e.g.collecteachpet’sname.

• Functionisthetypethattakesanobjectandreturnsanobjectofadifferenttype• akaTransformer

JCFExample

List<Pet>pets=...

List<String>petNames=newArrayList<String>();for(Petpet:pets){ petNames.add(pet.getName());}

10

COLLECTP


• Functionisthetypethattakesanobjectandreturnsanothertype.

EclipseCollec+onsExample(AnonymousInnerClassSyntax)

MutableList<Pet>pets=...

MutableList<String>petNames=pets.collect(newFunction<Pet,String>(){publicStringvalueOf(Petpet){returnpet.getName();}});

11

COLLECTP


• Functionisthetypethattakesanobjectandreturnsanothertype.

EclipseCollec+onsExample(Java8)

MutableList<Pet>pets=...

MutableList<String>petNames=pets.collect(pet->pet.getName());

MutableList<String>petNames=pets.collect(Pet::getName);

12

SELECTPATTERN

Itera+onPaLern

• SelectpaWern(akafilter).• ReturnstheelementsofacollecFonthatsaFsfysomecondiFon

• e.g.selectonlythosepeoplewhohaveapet.• Predicateisthetypethattakesanobjectandreturnsaboolean.

EclipseCollec+onsExample(AnonymousInnerClassSyntax)

MutableList<Person>people=...

MutableList<Person>petPeople=people.select(newPredicate<Person>(){publicbooleanaccept(Personperson){returnperson.isPetPerson();}}); 13

SELECTPATTERN

Itera+onPaLern

• SelectpaWern(akafilter).• ReturnstheelementsofacollecFonthatsaFsfysomecondiFon

• e.g.selectonlythosepeoplewhohaveapet.• Predicateisthetypethattakesanobjectandreturnsaboolean.

EclipseCollec+onsExample(Java8)

MutableList<Person>people=...

MutableList<Person>petPeople=people.select(person->person.isPetPerson());

14

ITERATIONP

ATTERNS

Examples

Collect ReturnsanewcollecFonwhereeachelementhasbeentransformed.

Select ReturnstheelementsofacollecFonthatsaFsfysomecondiFon.

CodeBlocks

• sortThis()takesaComparator,whichisastrategyinterface.• Similarly,collect()andselect()take“codeblock”parameters.• collect()takesaFunction.• select()takesaPredicate.• Don’tgethunguponthesenamesbecausetheIDEwillremindyou.

15

KATAINTRODUCTION

16

KATAIN

TRODU

CTION

Domain

• EclipseCollecFonsMiniKatausesPerson,Pet,PetType• Dataisavailabletoyouthroughthis.peoplewhichhassomepersonandpetobjectssetforyou

17

KATAIN

TRODU

CTION

Domain

18

KATAEXERCISE1

19

KATA

Exercise1

• FixExercise1Test;theyhavefailures.• Figureouthowtogettheteststopassusingwhatyouhaveseensofar.• Shouldtakeabout15minutes.

20

TESTUTILS

21

TESTUTILS

Verify

• EclipseCollecFonsdistribuFonincludeseclipse-collec+ons-testu+ls.jar.• IncludeshelpfuluFlityforwriFngunittests.• CollecFon-specific.• ImplementedasanextensionofJUnit.• BeWererrormessages• MostimportantclassiscalledVerify.

CodeExample

ExamplefromtheprevioussoluFonVerify.assertSize(2,peopleWithCats);InsteadofAssert.assertEquals(2,peopleWithCats.size());

22

FLATCOLLECTPATTERN

23

FLATCOLLECTP

ATTERNBackgroundoncollect()

• flatCollect()isaspecialcaseofcollect().• Withcollect(),whentheFunctionreturnsacollecFon,theresultisacollecFonofcollecFons.

CodeExampleMutableList<Person>people=...;Function<Person,Iterable<PetType>>function=

person->person.getPetTypes();

MutableList<MutableList<PetType>>pets=people.collect(function);

24

FLATCOLLECTP

ATTERNflatCollect()

• flatCollect()outputsasingle“flaWened”collecFoninsteadofacollecFonofcollecFons.

• ThesignatureofflatCollect()issimilartocollect(),exceptthattheFunctionparametermustmaptoanIterabletype.

flatCollect(Function<?superT,?extendsIterable<V>>function);

CodeExampleMutableList<Person>people=...;

MutableList<PetType>pets=people.flatCollect(person->person.getPetTypes());

25

MOREITERATIONPATTERNS

26

ITERATIONP

ATTERNS

OtherpaLernsthatusePredicate

Short-circuitpaLernsthatusePredicate

27

Select ReturnstheelementsofacollecFonthatsaFsfythePredicate.

Reject ReturnstheelementsofacollecFonthatdonotsaFsfythePredicate.

Count ReturnsthenumberofelementsthatsaFsfythePredicate.

Detect FindsthefirstelementthatsaFsfiesthePredicate.

AnySa+sfy ReturnstrueifanyelementsaFsfiesthePredicate.

AllSa+sfy ReturnstrueifallelementssaFsfythePredicate.

ITERATIONP

ATTERNS

InheritanceHierarchy

• MutableListextendsList.• FastListisadrop-inreplacementforArrayList.

28

Lists

ITERATIONP

ATTERNS

InheritanceHierarchy Sets

• MutableSetextendsSet.• UnifiedSetisadropinreplacementforHashSet.

29

“WITH”METHODS

30

“WITH”M

ETHODS

collectWith(),selectWith(),andrejectWith()

• collectWith(),selectWith(),andrejectWith()arealternateformsofcollect(),select(),andreject().

• Originalformsalltakeasingleparameter,acodeblockwhichtakesasingleparameter.

• Whatifwewanttofindgroupsofpeopleatdifferentages?

CodeExample

MutableList<Person>voters=people.select(person->person.getAge()>18;);

“WITH”M

ETHODS



• …with()formstaketwoparameters:• acodeblockwhichtakestwoparameters,• anobjectthatgetspassedasthesecondargumenttothecodeblock.

• Storethetwo-argumentblockinaconstanttoavoidobjectcreaFon.

CodeExample

Predicate2<Person,Integer>age=(person,age)->person.getAge()>age;MutableList<Person>drivers=people.selectWith(age,17);MutableList<Person>voters=people.selectWith(age,18);MutableList<Person>drinkers=people.selectWith(age,21);MutableList<Person>sunsetRobotSquad=people.selectWith(age,160);

“WITH”M

ETHODS

ForalmosteverycommoniteraFonpaWern,thereisanequivalent“With”method.

-  selectWith()-  detectWith()-  rejectWith()-  anySatisfyWith()…etc

Howtheycanbeused

Theseareusefulwhenyouwanttousemethodreferencesratherthanlambdas.

//doesnotcompileMutableList<Person>peopleWithCatsLambda=this.people.select(Person::hasPet(PetType.CAT));

33

“WITH”M

ETHODS

ForalmosteverycommoniteraFonpaWern,thereisanequivalent“With”method.

-  selectWith()-  detectWith()-  rejectWith()-  anySatisfyWith()…etc

Howtheycanbeused

Theseareusefulwhenyouwanttousemethodreferencesratherthanlambdas.

MutableList<Person>peopleWithCatMethodReference=

this.people.selectWith(Person::hasPet,PetType.CAT);

34

KATAEXERCISE2

35

KATA

Exercise2

• FixExercise2Test.• UsetheotheriteraFonpaWernsthattakeaPredicate.• UsetheflatCollectpaWern• Shouldtakeabout15minutes.

36

BAG

37

BAG

NewType

• UsefulwhenyouwouldotherwiseuseMap<K,Integer>• Forexample,findthenumberofeachpettype.

CodeExample

MutableList<Person>people=...;MutableList<PetType>pets=

people.flatCollect(Person::getPetTypes);MutableMap<PetType,Integer>petTypeCounts=

UnifiedMap.newMap();...intcats=petTypeCounts.get(PetType.CAT);

38

BAG

NewType

• UsefulwhenyouwouldotherwiseuseMap<K,Integer>• Forexample,findthenumberofeachpettype.• LotsofboilerplatecodetodealwithuniniFalizedcounts.

MapExample

MutableMap<PetType,Integer>petTypeCounts=UnifiedMap.newMap();

for(PetTypepetType:pets){Integercount=petTypeCounts.get(petType);if(count==null){count=0;}petTypeCounts.put(petType,count+1);} 39

BAG

NewType

•  Implementedasamapofkeytocount.• LikeaList,butunordered.• LikeaSet,butallowsduplicates.

BagExample

MutableBag<PetType>petTypeCounts=pets.toBag();intcat=petTypeCounts.occurrencesOf(PetType.CAT);

40

BAG

BagAPI

CodeExample

MutableBag<String>bag=HashBag.newBagWith("one","two","two","three","three","three");

Assert.assertEquals(3,bag.occurrencesOf("three"));

bag.add("one");Assert.assertEquals(2,bag.occurrencesOf("one"));

bag.addOccurrences("one",4);Assert.assertEquals(6,bag.occurrencesOf("one"));

41

Methods Inheritedfrom

select(),collect(),etc. RichIterableadd(),remove(),iterator(),etc.

MutableCollection(java.util.Collection)

occurrencesOf(),forEachWithOccurrences(),toMapOfItemToCount()

Bag

addOccurrences(),removeOccurrences() MutableBag

MULTIMAP

42

MULTIM

APNewType

• MultimapissimilartoMap,butassociatesakeytomul=plevalues.• UsefulwhenyouwouldotherwiseuseMap<K,Collection<V>>

• Forexample,findwhichpeoplehavethesamelastname.

CodeExample

MutableList<Person>people=...;MutableMap<String,MutableList<Person>>

lastNamesToPeople=UnifiedMap.newMap();...MutableList<Person>smiths=

lastNamesToPeople.get("Smith");43

MULTIM

APNewType

• MultimapissimilartoMap,butassociatesakeytomul=plevalues.• UsefulwhenyouwouldotherwiseuseMap<K,Collection<V>>

• Forexample,findwhichpeoplehavethesamelastname.• LotsofboilerplatecodetodealwithuniniFalizedbackingcollecFons.

MapExample

MutableMap<String,MutableList<Person>>lastNamesToPeople=UnifiedMap.newMap();

for(Personperson:people){StringlastName=person.getLastName();MutableList<Person>peopleWithLastName=

lastNamesToPeople.get(lastName);if(peopleWithLastName==null){peopleWithLastName=FastList.newList();lastNamesToPeople.put(lastName,peopleWithLastName);}peopleWithLastName.add(person);} 44

MULTIM

APBefore

A\er

45

MutableMap<String,MutableList<Person>>lastNamesToPeople=UnifiedMap.newMap();

for(Personperson:people){StringlastName=person.getLastName();MutableList<Person>peopleWithLastName=

lastNamesToPeople.get(lastName);if(peopleWithLastName==null){peopleWithLastName=FastList.newList();lastNamesToPeople.put(lastName,peopleWithLastName);}peopleWithLastName.add(person);}

MutableListMultimap<String,Person>lastNamesToPeople=people.groupBy(Person.TO_LAST_NAME);MutableList<Person>smiths=

lastNamesToPeople.get("Smith");

MULTIM

APMul+map

• Whathappensifyouaddthesamekeyandvaluetwice?

CodeExample

MutableMultimap<String,Person>multimap=...;multimap.put("Smith",person);multimap.put("Smith",person);RichIterable<Person>smiths=

multimap.get("Smith");

Verify.assertIterableSize(?,smiths);46

MULTIM

APMul+map

• Whathappensifyouaddthesamekeyandvaluetwice?• DependsonthetypeofthebackingcollecFon.

CodeExample

MutableListMultimap<String,Person>multimap=FastListMultimap.newMultimap();multimap.put("Smith",person);multimap.put("Smith",person);MutableList<Person>smiths=multimap.get("Smith");

Verify.assertIterableSize(2,smiths);47

MULTIM

APMul+map

• Whathappensifyouaddthesamekeyandvaluetwice?• DependsonthetypeofthebackingcollecFon.

CodeExample

MutableSetMultimap<String,Person>multimap=UnifiedSetMultimap.newMultimap();multimap.put("Smith",person);multimap.put("Smith",person);MutableSet<Person>smiths=multimap.get("Smith");

Verify.assertIterableSize(1,smiths);48

MULTIM

APgroupByEach()

• groupByEach()isaspecialcaseofgroupBy().• Analogoustothedifferencebetweencollect()andflatCollect().• AppropriatewhentheFunctionreturnsacollecFon.• ThereturntypeisthesameasgroupBy().

CodeExampleMutableListMultimap<String,Person>lastNamesToPeople=people.groupBy(LAST_NAME_FUNCTION);MutableListMultimap<PetType,Person>petsToPeople=people.groupByEach(PET_TYPE_FUNCTION);

49

TARGETCOLLECTIONS

50

TARGETCOLLECTIO

NS

Itera+onPaLern

• Let'ssaywehave3people:mrSmith,mrsSmith,mrJones.• Thefirsttwosharethesameaddress.• Whatwillgetprintedbythefollowingcode?

ExampleCode

MutableSet<Person>people=UnifiedSet.newSetWith(mrSmith,mrsSmith,mrJones);intnumAddresses=people.collect(addressFunction).size();System.out.println(numAddresses);

51

TARGETCOLLECTIO

NS

Covariantreturntypes

• select(),collect(),etc.aredefinedwithcovariantreturntypes:

• MutableCollection.collect()returnsaMutableCollection• MutableList.collect()returnsaMutableList• MutableSet.collect()returnsaMutableSet

• AlternateformstaketargetcollecFons.

ExampleCode

MutableSet<Person>people=UnifiedSet.newSetWith(mrSmith,mrsSmith,mrJones);intnumAddresses=people.collect(addressFunction).size();System.out.println(numAddresses);

52

TARGETCOLLECTIO

NS

Covariantreturntypes

• select(),collect(),etc.aredefinedwithcovariantreturntypes:

• MutableCollection.collect()returnsaMutableCollection• MutableList.collect()returnsaMutableList• MutableSet.collect()returnsaMutableSet

• AlternateformstaketargetcollecFons.

ExampleCode

MutableSet<Person>people=UnifiedSet.newSetWith(mrSmith,mrsSmith,mrJones);

MutableList<Address>targetList=FastList.<Address>newList();intnumAddresses=

people.collect(addressFunction,targetList).size();System.out.println(numAddresses); 53

KATAEXERCISE3

54

KATA

Exercise3

• FixExercise3Test.• UseBag,MulFmap.• Shouldtakeabout10minutes.

55

PRIMITIVECOLLECTIONS

PRIM

ITIVECOLLECTIO

NS

EachdatastructurehasanequivalentprimiFveside.EclipseCollecFonssupportsallprimiFves–int,double,short,long,

float,boolean,char,byte

57

PRIM

ITIVECOLLECTIO

NS

ClassDiagram

PrimiFveIterable IntIterable

MutableIntCollecFon

MutableIntList

MutableIntSet

MutableIntBag

LazyIntIterable

ImmutableIntCollecFon

ImmutableIntList

ImmutableIntSet

ImmutableIntBag

58

PRIM

ITIVECOLLECTIO

NS

Primi+veAPI

ThereisalsothesamerichandfluentAPIthatthenonprimiFvesideoffers.

Examples

MutableIntListintListOfAges=this.people.flatCollect(Person::getPets) .collectInt(Pet::getAge);

MutableIntListselection= intListOfAges.select(age->age>2);

MutableIntSetintSetOfAges=intListOfAges.toSet();

59

KATAEXERCISE4

60

KATA

Exercise4

• FixExercise4Test.• RefactorJava8streamstoEclipseCollecFons.• Shouldtakeabout20minutes.

61

KATAEXERCISE5

62

KATA

Exercise4

• FixExercise5Test.• Thisisextra-credit• Usetargetversions,methodsonRichIterable• Shouldtakeabout20minutes.

63

APPENDIX

64

ANONYMOUSINNERCLASS

65

ANONYM

OUSIN

NERC

LASSDefini+on

• Aninnerclasswithnoname.• Lookslikeanormalconstructorcall,butitworksonabstracttypes(includinginterfaces).

• HasabodyarerwardswhichmakesthetypeconcreteoroverridesmethoddefiniFons.

• Hasarandom-lookingclassnamearercompilaFon.• OuterClass$1forthefirstanonymousinnerclassinOuterClass.

CodeExample

Comparator<Person>comparator=newComparator<Person>(){publicintcompare(Persono1,Persono2){returno1.getLastName().compareTo(o2.getLastName());}};System.out.println(comparator.getClass());

66

CLOSURE

67

CLO

SURE

ClosureDefini+on

WikipediadefiniFon:“[A]closureisafirst-classfuncFonwithfreevariablesthatareboundinthelexicalenvironment.“SuchafuncFonissaidtobe‘closedover’itsfreevariables.“Aclosureisdefinedwithinthescopeofitsfreevariables,andtheextentofthosevariablesisatleastaslongasthelifeFmeoftheclosureitself.”

•  Javadoesnothaveclosures.•  Java8haslambdas.

68

CLO

SURE

ClosureDefini+on

Javadoesnothaveclosures.Inthecodeexample,thePredicateisaclasswithaStringfield.Itisnotthesamecopyasthemethodparameter.

CodeExample

publicCustomergetCustomerNamed(Stringname){Predicate<Customer>customerNamed=Predicates.attributeEqual(Customer.TO_NAME,name);returnthis.customers.detect(customerNamed);}

69

CLO

SURE

ClosureDefini+on

Javadoesnothaveclosures.Inthecodeexample,thePredicateisaclasswithaStringfield.Itisnotthesamecopyasthemethodparameter.•  Changingthiscopyofnamehasnoeffectontheresult.• MaybeobviousbecauseofJava’srulesforparameterpassing.

CodeExample

publicCustomergetCustomerNamed(Stringname){Predicate<Customer>customerNamed=Predicates.attributeEqual(Customer.TO_NAME,name);name=name+"!";returnthis.customers.detect(customerNamed);}

70

CLO

SURE

ClosureDefini+on

Javadoesnothaveclosures.Inthecodeexample,thePredicateisaclasswithaStringfield.Itisnotthesamecopyasthemethodparameter.•  IfyouuseananonymousinnerclasstoimplementthePredicate,youhavetomakenamefinalinordertosaFsfythecompiler.

CodeExample

publicCustomergetCustomerNamed(finalStringname){Predicate<Customer>attributeEqual=newPredicate<Customer>(){publicbooleanaccept(Customercustomer){returncustomer.getName().equals(name);}};returnthis.customers.detect(attributeEqual);} 71

CLO

SURE

ClosureDefini+on

Javadoesnothaveclosures.Inthecodeexample,thePredicateisaclasswithaStringfield.Itisnotthesamecopyasthemethodparameter.•  IfyouuseananonymousinnerclasstoimplementthePredicate,youhavetomakenamefinalinordertosaFsfythecompiler.

•  Refactortheanonymousinnerclasstoanamedinnerclassandyoucanseewhy.

CodeExample

privatestaticfinalclassCustomerNamedimplementsPredicate<Customer>{

privatefinalStringname;privateCustomerNamed(Stringname){this.name=name;}publicbooleanaccept(Customercustomer){returncustomer.getName().equals(this.name);}} 72

BLOCKS

73

BLO

CKSUML

74

BLO

CKSFunc+on

Functiontransformsonetype(T)toanother(V):publicinterfaceFunction<T,V>extendsSerializable{VvalueOf(Tobject);}

Usedin:• collect• flatCollect• groupBy• minBy• maxBy• toSortedListBy• sortThisBy• toMap

75

BLO

CKSPredicate

Predicatetakesanobjectofsometype(T)andreturnsaboolean:publicinterfacePredicate<T>extendsSerializable{booleanaccept(finalTeach);}

Usedin:• select• reject• detect• count• anySatisfy• allSatisfy

76

BLO

CKSPredicate

Proceduretakesanobjectofsometype(T)anddoesn’treturnanything:publicinterfaceProcedure<T>extendsSerializable{voidvalue(finalTeach);}

Usedin:• forEach

77

RICHITERABLE

78

RICHITERABLE

CheatSheet

79

collect TransformselementsusingaFunctionintoanewcollecFon.

flatCollect TransformsandflaWenstheelementsusingaFunction.

groupBy GetsakeyforeachelementusingaFunctionandputsthekeyandelementintoaMultimap.

RICHITERABLE

CheatSheet

80

sortThisBy GetssomeaWributefromeachelementusingaFunctionandsortsthelistbythenaturalorderofthataWribute.

toSortedListBy GetssomeaWributefromeachelementusingaFunctionandreturnsanewlistsortedbythenaturalorderofthataWribute.

minBy GetssomeaWributefromeachelementandreturnstheelementwhoseaWributeisminimal.

maxBy GetssomeaWributefromeachelementandreturnstheelementwhoseaWributeismaximal.

toMap GetsakeyandvalueforeachelementusingtwoFunctionsandreturnsanewmapcontainingallthekey/valuepairs.

RICHITERABLE

CheatSheet

81

select ReturnstheelementsofacollecFonthatsaFsfysomecondiFon(Predicate).

reject ReturnstheelementsofacollecFonthatdonotsaFsfythePredicate.

detect FindsthefirstelementthatsaFsfiesthePredicate.

count ReturnsthenumberofelementsthatsaFsfythePredicate.

anySatisfy ReturnstrueifanyelementsaFsfiesthePredicate.

allSatisfy ReturnstrueifallelementssaFsfythePredicate.

forEach ExecutestheProcedureoneachelement,doesn'treturnanything.

RICHITERABLE

CheatSheet

82

min ReturnstheminimumelementusingeitherthenaturalorderoraComparator.

max ReturnsthemaximumelementusingeitherthenaturalorderoraComparator.

toSortedList Returnsanewlist,sortedusingeitherthenaturalorderoraComparator.

makeString ConvertsthecollecFontoastringusingopFonalstart,end,andseparatorstrings.

appendString ConvertsthecollecFontoastringandappendsittoanAppendable.

zip TakesasecondRichIterableandpairsupalltheelements.IfoneofthetwoRichIterablesislongerthantheother,itsremainingelementsareignored.

zipWithIndex ZipsthecollecFonwiththeIntegerindexes0ton-1.

chunk SplitsacollecFonintofixedsizechunks.ThefinalchunkwillbesmallerifthecollecFondoesn'tdivideevenly.

RICHITERABLE

InheritanceHierarchy

83

BAG

ClassDiagram

Iterable RichIterable

MutableCollecFon

MutableList

MutableSet

MutableBag

ImmutableCollecFon

ImmutableList

ImmutableSet

ImmutableBag

84

BAG

ClassDiagram

RichIterable Bag

MutableBag

HashBag

SynchronizedBag

UnmodifiableBagImmutableBag

85

MULTIM

APClassDiagram

MulFmap

MutableMulFmap

MutableListMulFmap

MutableSetMulFmap

MutableBagMulFmap

ImmutableMulFmap

ImmutableListMulFmap

ImmutableSetMulFmap

ImmutableBagMulFmap

86

OPTIMIZATION

87

OPTIM

IZATION



• Originalformsalltakeasingleparameter,acodeblockwhichtakesasingleparameter.

• Whatifwewanttofindgroupsofpeopleatdifferentages?

CodeExample

MutableList<Person>voters=people.select(person->person.getAge()>18;);

88

OPTIM

IZATION



• …with()formstaketwoparameters:• acodeblockwhichtakestwoparameters,• anobjectthatgetspassedasthesecondargumenttothecodeblock.

• Storethetwo-argumentblockinaconstanttoavoidobjectcreaFon.

CodeExample

Predicate2<Person,Integer>age=(person,age)->person.getAge()>age;MutableList<Person>drivers=people.selectWith(age,17);MutableList<Person>voters=people.selectWith(age,18);MutableList<Person>drinkers=people.selectWith(age,21);MutableList<Person>sunsetRobotSquad=people.selectWith(age,160);

89

OPTIM

IZATION

“Weshouldforgetaboutsmallefficiencies,sayabout97%oftheFme:prematureopFmizaFonistherootofallevil”

–DonaldKnuth

90

Learn more at GS.com/Engineering

© 2016 Goldman Sachs. This presentation should not be relied upon or considered investment advice. Goldman Sachs does not warrant or guarantee to anyone the accuracy, completeness or efficacy of this presentation, and recipients should not rely on it except at their own risk. This presentation may not be forwarded or disclosed except with this disclaimer intact.

Documents

Eclipse Collec+ons and Java 8 Lambdas · • java.util.Collections provides methods for sort(), min(), max() and just a few others. • The most common iteraon paerns are missing: