Why not use Kotlin? - Kotlin for Java Developers

-:$PSQPSBUJPO 8IZOPUVTF,PUMJO ,PUMJOGPS+BWB%FWFMPQFST ++6($$$'BMM )POEB:BTVIJTB

-:$PSQPSBUJPO 5BSHFUT ❌,PUMJO&YQFSUT ❌$PSFUFDIOJDBMBTQFDUT✅8JEFMZQSBHNBUJDBTQFDUT ❌1FPQMFXIPMPWFPOMZ+BWB ✅,PUMJO/FXCJFT ✅5IPTFDPOTJEFSJOHNJHSBUJPOGSPN+BWBUP,PUMJO

-:$PSQPSBUJPO "HFOEB 8IBUJT,PUMJO (SPXUIPGUIF,PUMJOFDPTZTUFN ,PUMJOWT+BWB$PNQBSJTPOGFBUVSFT +BWBJOUFSPQFSBCJMJUZ

-:$PSQPSBUJPO 8IBUJT,PUMJO 8IBUJT,PUMJO %FTJHOFE%FWFMPQFECZ+FU#SBJOT 0QFOTPVSDF HJUIVCDPN+FU#SBJOTLPUMJO
.VMUJQBSBEJHN 001 '1 %FDMBSBUJWF .VMUJQMBUGPSN ,PUMJO+7. ,PUMJO/BUJWF ,PUMJO+4 ,PUMJO8"4. *OJUJBMMZEFTJHOFEGPSTFSWFSTJEFBOEEFTLUPQBQQMJDBUJPOPOUIF+7.<> (PPHMFBOOPVODFEPGGJDJBMTVQQPSUPO"OESPJE!(PPHMF*0b <>IUUQTXXXBCSFTMBWDPNCJP

-:$PSQPSBUJPO ,PUMJO`TQIJMPTPQIZ 8IBUJT,PUMJO Language design is cast in stone,
but this stone is reasonably soft, and with some effort we can reshape it later. Kotlin Design Team 1SJODJQMFTPGQSBHNBUJDFWPMVUJPOIUUQTLPUMJOMBOHPSHEPDTLPUMJOFWPMVUJPOQSJODJQMFTIUNM Kotlin is a pragmatic programming language … and is focused on interoperability, safety, clarity, and tooling support. Andrey Breslav, Lead Language Designer IUUQTCMPHKFUCSBJOTDPNLPUMJOLPUMJOSFMFBTFEQSBHNBUJDMBOHVBHFGPSKWNBOEBOESPJE 1SBHNBUJD 0QFOUPDPNNVOJUZGFFECBDL JTTVFT CVHT QSPQPTBMT

-:$PSQPSBUJPO (SPXUIPGUIF,PUMJOFDPTZTUFN (SPXUIPGUIF,PUMJOFDPTZTUFN -BOHVBHF 9999

,$PNQJMFS $PNQJMFS1MVHJOT "MMPQFO /PBSH LTQ 1PXFSBTTFSU ʜ

,$PNQJMFS $PNQJMFS1MVHJOT "MMPQFO /PBSH LTQ 1PXFSBTTFSU ʜ 5PPMJOH *OUFMMJ+*%&" ,PUMJO/PUFCPPL -JLFB+VQZUFS/PUFCPPL

,$PNQJMFS $PNQJMFS1MVHJOT "MMPQFO /PBSH LTQ 1PXFSBTTFSU ʜ 5PPMJOH *OUFMMJ+*%&" ,PUMJO/PUFCPPL -JLFB+VQZUFS/PUFCPPL .VMUJQMBUGPSN ,PUMJO+7. 4FSWFSTJEF "OESPJE "35 ,PUMJO/BUJWF CBDLFOE--7. J04 4XJGU0CK$JOUFSPQ ,PUMJO+4 'SPOUFOE#BDLFOE$-* ,PUMJO8BTN 8FCCSPXTFS

-:$PSQPSBUJPO 4FSWFS4JEF,PUMJO (SPXUIPGUIF,PUMJOFDPTZTUFN

-:$PSQPSBUJPO 4FSWFS4JEF,PUMJO (SPXUIPGUIF,PUMJOFDPTZTUFN 4FSWFS4JEF,PUMJO ,PUMJOY4QSJOH "4USBUFHJD1BSUOFSTIJQ 3FG IUUQTCMPHKFUCSBJOTDPNLPUMJOTUSBUFHJDQBSUOFSTIJQXJUITQSJOH
IUUQTLPUMJODPOGDPNUBMLT

-:$PSQPSBUJPO 4FSWFS4JEF,PUMJO (SPXUIPGUIF,PUMJOFDPTZTUFN 4FSWFS4JEF,PUMJO &OIBODFOVMMTBGFUZ 'BTUFS,PUMJOSFGMFDUJPO
&WPMWFDPOGJHVSBUJPO%4-T ,PUMJOY4QSJOH "4USBUFHJD1BSUOFSTIJQ 3FG IUUQTCMPHKFUCSBJOTDPNLPUMJOTUSBUFHJDQBSUOFSTIJQXJUITQSJOH IUUQTLPUMJODPOGDPNUBMLT

-:$PSQPSBUJPO 4FSWFS4JEF,PUMJO (SPXUIPGUIF,PUMJOFDPTZTUFN 4FSWFS4JEF,PUMJO &OIBODFOVMMTBGFUZ 'BTUFS,PUMJOSFGMFDUJPO
&WPMWFDPOGJHVSBUJPO%4-T ,PUMJOY4QSJOH "4USBUFHJD1BSUOFSTIJQ 3FG IUUQTCMPHKFUCSBJOTDPNLPUMJOTUSBUFHJDQBSUOFSTIJQXJUITQSJOH IUUQTLPUMJODPOGDPNUBMLT 3PE+PIOTPO`TUBMLT ,PUMJOBOE4QSJOH5IFNPEFSO TFSWFSTJEFTUBDLc,PUMJO$POG $SFBUPSPG4QSJOH/PEFTJSFUPXSJUF +BWBc5BMLJOH,PUMJO

-:$PSQPSBUJPO 4ZOUBY ,PUMJOWT+BWB

-:$PSQPSBUJPO /BNFE"SHVNFOUT ,PUMJOWT+BWB4ZOUBY class Person { String id; String
name; Integer age; String address; String email; String phoneNumber; } final Person person = new Person( "1", “James Gosling", null, “Canada", null, null ); +BWB

name; Integer age; String address; String email; String phoneNumber; } final Person person = new Person( "1", “James Gosling", null, “Canada", null, null ); +BWB class Person ( val id: String, val name: String, val age: Int?, val address: String, val email: String?, val phoneNumber: String?, ) val person = Person( id = "2", name = "Andrey Breslav", age = null, address = "Tokyo", email = null, phoneNumber = null ) ,PUMJO

name; Integer age; String address; String email; String phoneNumber; } final Person person = new Person( "1", “James Gosling", null, “Canada", null, null ); +BWB class Person ( val id: String, val name: String, val age: Int?, val address: String, val email: String?, val phoneNumber: String?, ) val person = Person( id = "2", name = "Andrey Breslav", age = null, address = “Russia", email = null, phoneNumber = null ) ,PUMJO 3FEVDFDPHOJUJWFMPBEJNQMFNFOUBUJPOFSSPST PSNJTUBLFT

-:$PSQPSBUJPO &YUFOTJPO ,PUMJOWT+BWB4ZOUBY &YQBOEFYJTUJOHDMBTTFTXJUIOFXGVODUJPOT

-:$PSQPSBUJPO &YUFOTJPO ,PUMJOWT+BWB4ZOUBY &YQBOEFYJTUJOHDMBTTFTXJUIOFXGVODUJPOT -JCSBSJFT 0VUDPNF
3FBEBCJMJUZ 4FNBOUJDT // not using extension fun convertToCalendarFormat(date: LocalDate): String { val f = DateTimeFormatter.ofPattern("yyyy/MM/dd") return date.format(f) } // Using extension fun LocalDate.toCalendarFormat(): String { val f = DateTimeFormatter.ofPattern("yyyy/MM/dd") return this.format(f) } // GOOD LocalDate.now().toCalendarFormat() // NOT GOOD convertToCalendarFormat(LocalDate.now())

-:$PSQPSBUJPO &YUFOTJPO ,PUMJOWT+BWB4ZOUBY &YQBOEFYJTUJOHDMBTTFTXJUIOFXGVODUJPOT -JCSBSJFT (FOFSBUFEDPEF
FH0QFO"1* 1SPUPCVG 0VUDPNF 3FBEBCJMJUZ 4FNBOUJDT 4FQBSBUJPOPG$PODFSOT EPNBJOMBZFS㲗SFQPTJUPSZMBZFS /** It’s a generated class, do not edit it manually. **/ class PersistUserRequest ( var userId: String? = null, var username: String? = null, ) class GetUserResponse ( var userId: String? = null, var username: String? = null, ) fun PersistUserRequest.toUser(): User { return User( id = requireNotNull(this.userId), name = requireNotNull(this.username), ) } fun User.toResponse(): GetUserResponse { return GetUserResponse( userId = requireNotNull(this.id), username = requireNotNull(this.name), ) } val requestUser: User = requestDTO.toUser() val response = user.toResponse()

-:$PSQPSBUJPO &YUFOTJPO ,PUMJOWT+BWB4ZOUBY &YQBOEFYJTUJOHDMBTTFTXJUIOFXGVODUJPOT -JCSBSJFT (FOFSBUFEDPEF
FH 0QFO"1* 1SPUPCVG 0VUDPNF 3FBEBCJMJUZ 4FNBOUJDT 4FQBSBUJPOPG$PODFSOT EPNBJOMBZFS㲗SFQPTJUPSZMBZFS /PUPOMZGVODUJPO CVUBMTPQSPQFSUZ DPNQBOJPOPCKFDU

-:$PSQPSBUJPO $MBTTFT ,PUMJOWT+BWB4ZOUBY %BUB$MBTT 'PSIPMEJOHEBUB "VUPNBUJDBMMZHFOFSBUFDPEF
equals()hashCode() toString() copy() componentN() DPOTUSVDUPS componentN()ʜ%FTUSVDUVSJOHEFDMBSBUJPOTFHval (x, y) = cartesian 7BMVF$MBTT 'PSXSBQQJOHBWBMVFUPDSFBUFEPNBJOTQFDJGJDUZQF 0QUJNJ[F JOMJOFPSCPYJOH 3FEVDFNFNPSZBMMPDBUJPODPTUT($DPTUT 4FBMFE$MBTT*OUFSGBDF

-:$PSQPSBUJPO 0UIFSTZOUBY ,PUMJOWT+BWB4ZOUBY

-:$PSQPSBUJPO 0UIFSTZOUBY ,PUMJOWT+BWB4ZOUBY 4NBSU$BTU +BWB+&1l1BUUFSO.BUDIJOHGPSJOTUBODFPGz 3FMFBTFE
+BWB+&1l1BUUFSO.BUDIJOHGPSTXJUDIz 3FMFBTFE 4USJOH5FNQMBUFT +BWB+&1l4USJOH5FNQMBUFTz 8JUIESBXO QFOEJOHSFEFTJHO 0QFSBUPSPWFSMPBE 6TF+, -CZPWFSMPBEJOHɹplus() minus() %FGBVMUBSHVNFOUWBSBSHT (PPECZFUP+BWB`TPWFSMPBEIFMM

-:$PSQPSBUJPO /VMM4BGFUZ ,PUMJOWT+BWB

-:$PSQPSBUJPO /VMM4BGFUZ ,PUMJOWT+BWB/VMM4BGFUZ +BWB 55PSOVMM ,PUMJO 55
5 5PSOVMM

-:$PSQPSBUJPO ,PUMJOWT+BWB/VMM4BGFUZ // not null safety public static String
findNameById(Integer id) { final User user = users.get(id); if (user != null) { return user.getName(); } return null; } final String name = findNameById(1).toUpperCase(); +BWB 55PSOVMM ,PUMJO 55 5 5PSOVMM

-:$PSQPSBUJPO public static String findNameById(@NonNull Integer id) { final User
user = users.get(id); if (user != null) { return user.getName(); } return null; } // not null safety final String name = findNameById(1).toUpperCase(); ,PUMJOWT+BWB/VMM4BGFUZ +BWB 55PSOVMM 'PS4BGFUZ !/PO/VMM ,PUMJO 55 5 5PSOVMM

-:$PSQPSBUJPO public static Optional<String> findNameById(@NonNull Integer id) { final User
user = users.get(id); if (user != null) { return Optional.of(user.getName()); } return Optional.empty(); } final String name = findNameById(1).map(String::toUpperCase).orElse(null); ,PUMJOWT+BWB/VMM4BGFUZ +BWB 55PSOVMM 'PS4BGFUZ !/PO/VMM 0QUJPOBM5 ,PUMJO 55 5 5PSOVMM

-:$PSQPSBUJPO ,PUMJOWT+BWB/VMM4BGFUZ +BWB 55PSOVMM 'PS4BGFUZ !/PO/VMM
0QUJPOBM5 ,PUMJO 55 5 5PSOVMM 'PS4BGFUZʜ

-:$PSQPSBUJPO ,PUMJOWT+BWB/VMM4BGFUZ fun findNameById(id: Int): String? = users[id]?.name val
name = findNameById(2)?.uppercase() +BWB 55PSOVMM 'PS4BGFUZ !/PO/VMM 0QUJPOBM5 ,PUMJO 55 5 5PSOVMM 'PS4BGFUZʜ /PUIJOH &YQMJDJUOVMMBCJMJUZ4BGFDBMMT

-:$PSQPSBUJPO ,PUMJOWT+BWB/VMM4BGFUZ fun findNameById(id: Int): String? = users[id]?.name val
name = findNameById(2)?.uppercase() $PNQBSFEUP+BWB ,PUMJOʜ /POFFEGPS"OOPUBUJPOT /POFFEGPSOptional 4BGFDBMMTTJNQMJGZOVMMIBOEMJOH public static Optional<String> findNameById(@NonNull Integer id) { final User user = users.get(id); if (user != null) { return Optional.of(user.getName()); } return Optional.empty(); } final String name = findNameById(1).map(String::toUpperCase).orElse(null);

-:$PSQPSBUJPO "TZODISPOPVT $PODVSSFODZ 1BSBMMFMJTN ,PUMJOWT+BWB

-:$PSQPSBUJPO ,PUMJOWT+BWB"TZODISPOPVT$PODVSSFODZ1BSBMMFMJTN +BWB 5ISFBEʜ04UISFBE &YFDVUPS "TZOD"1*T /*0
3FBDUPS 'VUVSF $PNQMFUBCMF'VUVSF .PEFSO+BWB 7JSUVBM5ISFBET MJHIUXFJHIUUISFBE %FUFDU8BJUFH#MPDLJOH*0 04UISFBEVONPVOUNPVOU ,PUMJO $PSPVUJOF DPPQFSBUJWFUBTL TVTQFOESFTVNF OPOCMPDLJOH TVTQFOEGVODUJPO %JTQBUDIFS UISFBEQPPMFSTDIFEVMFS ⚠ /05& ❌ #MPDLJOH 5ISFBE-PDBM QSPQBHBUFDPOUFYU

-:$PSQPSBUJPO 4PVSDFPG$PODFSO ,PUMJOWT+BWB "MMFYDFQUJPOBSFlVODIFDLFEz Result<T>IBTPOMZ5ISPXBCMFPOGBJMVSF*UEPFTO`UNBUDIEPNBJOFSSPST 8PSL"SPVOET
4FMGJNQMFNFOUBUJPO 5IJSE1BSUZ BSSPXLUBSSPX NJDIBFMCVMMLPUMJOSFTVMU ,&&13JDI&SSPST &SSPS6OJPO5ZQF &SSPS)BOEMJOH

-:$PSQPSBUJPO +BWBJOUFSPQFSBCJMJUZ +BWBJOUFSPQFSBCJMJUZ +BWBDBODBMM,PUMJO ,PUMJODBODBMM+BWB (FOFSBMMZ l3FDPEFzQSPKFDUT
.JHSBUJPOVOJUQFSBQQMJDBUJPO *ODBTFPG +BWB,PUMJO .JHSBUJPOVOJUQFSDMBTT&BTZ4BGF.JHSBUJPO

-:$PSQPSBUJPO +BWBJOUFSPQFSBCJMJUZ +BWBJOUFSPQFSBCJMJUZ +BWBDBODBMM,PUMJO ,PUMJODBODBMM+BWB (FOFSBMMZ l3FDPEFzQSPKFDUT
.JHSBUJPOVOJUQFSBQQMJDBUJPO *ODBTFPG +BWB,PUMJO .JHSBUJPOVOJUQFSDMBTT&BTZ4BGF.JHSBUJPO ⚠ /05& /VMMBCJMJUZ 1MBUGPSNUZQFT 55PS5 .VUBCJMJUZ NVUBCMFJNNVUBCMF &YDFQUJPO)BOEMJOH

-:$PSQPSBUJPO 5BLFBXBZ ,PUMJOJTQPXFSGVMQSBHNBUJD 4ZOUBY /VMM4BGFUZ $PSPVUJOFT ʜ
(SPXJOH&DPTZTUFN (SFBU+BWBJOUFSPQFSBCJMJUZFBTZNJHSBUJPO "TUSPOHBMUFSOBUJWFGPS+BWBEFWFMPQFST

-:$PSQPSBUJPO 8IZOPUVTF,PUMJO

-:$PSQPSBUJPO -:$PSQPSBUJPO 5IBOL:PV

Why not use Kotlin? - Kotlin for Java Developers

Why not use Kotlin? - Kotlin for Java Developers

More Decks by Yasuhisa Honda

Featured

Transcript