How to start Kotlin APP DOJO

by satorufujiwara

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ࠓ͔Β࢝ΊΔKotlinʹΑΔAndroidΞϓϦ։ൃ 2017.08.29 APP_DOJO @satorufujiwara

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About me Satoru Fujiwara (@satorufujiwara) Android Engineer @CyberAgent ,Inc Shibuya.apk

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Kotlin & Me FRESH! ΛKotlinͰ։ൃ (2015೥3݄ʙ) Kotlin Advent Calendar (2015/2016) -ʮ2016೥ɺKotlinͰAndroid։ൃ͢Δํ΁ʯ @Qiita ( goo.gl/0medax ) APP DOJO ʮKotlin in Google I/O 2017ʯ(2017/05/25) Kotlinೖ໳·Ͱͷॿ૸ಡຊ ( goo.gl/5vUT7o )

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Kotlinೖ໳·Ͱͷॿ૸ಡຊ • ೔ຊKotlinϢʔβάϧʔϓͷ໊લͰ༗ࢤ 9໊Ͱࣥච • Google I/O 2017ͰKotlinͷΦϑΟγϟ ϧԽ͕ൃද͞Εͨޙɺ1िؒͰॻ͍ͨ • ແྉͰެ։ ( goo.gl/5vUT7o )

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“ͱ͸ݴͬͯ΋ɺࠓճͷൃදͰ͸͡Ίͯ Kotlin ͱ͍͏ϓϩάϥϛ ϯάݴޠΛࣖʹͨ͠։ൃऀ΋ଟ͍͘Δ͜ͱͰ͠ΐ͏ɻ ʮKotlin ͱ͸Կͩ?ʯͱ͔ʮͳΜͰ Kotlinͳͷ͔?ʯͱ͔ʮͲ͏ ΍ֶͬͯ΂͹͍͍ͷ͔?ʯͱ͍͏ށ࿭͍΋͋Δ͔ͱࢥ͍·͢ɻ ͦ͜Ͱ… “ Kotlinೖ໳·Ͱͷॿ૸ಡຊɺલॻ͖ΑΓ

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ຊ೔ͷGoal • ʮKotlin ͱ͸Կͩʁʯ • ʮͳΜͰ Kotlinͳͷ͔ʁʯ • ʮͲ͏΍ֶͬͯ΂͸ྑ͍ͷ͔ʁʯ

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ຊ೔ͷGoal • ʮKotlin ͱ͸Կͩʁʯˠ Kotlinͷߟ͑ํʹ͍ͭͯ஌Δ • ʮͳΜͰ Kotlinͳͷ͔ʁʯˠ KotlinͷݴޠػೳΛ஌Δ • ʮͲ͏΍ֶͬͯ΂͸ྑ͍ͷ͔ʁʯˠ KotlinΛ࢝ΊΔͨΊͷπʔϧΛ஌Δ

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Kotlinͷߟ͑ํ

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Kotlin in Action • Kotlinͷ։ൃνʔϜʹΑͬͯॻ͔Εͨຊ • Kotlinͷίϯηϓτ͔ΒKotlinͷݴޠػೳΛجຊ ػೳ(if/when/ΫϥεͳͲ)͔Βൃలػೳ(nullable/ lambda/ߴ֊ؔ਺/૯শܕ)·ͰΧόʔ • ࠓ೔ͷϓϨθϯͷલ൒͸͜ͷຊͷ಺༰ʹ͔ͳΓԊͬ ͍ͯ·͢

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Kotlin in Action • ຋༁ຊग़·͢ʂ • ༁ऀ • ௕ᖒଠ࿠ @ngsw_taro • ࢁຊ७ฏ @boohbah • yy_yank @yy_yank • ౻ݪ੟ @satorufujiwara

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Kotlin ͕໨ࢦ͍ͯ͠Δͱ͜Ζ • ݱࡏ Java ͕࢖Θ͍ͯΔ؀ڥʹɺΑΓ؆ܿ ͰɺΑΓੜ࢈ੑ͕ߴ͘ɺΑΓ ҆શͳ Java ͷ୅ସݴޠΛఏڙ͢Δ͜ͱ • ݱঢ়ͩͱAndroidͱαʔόʔαΠυ • কདྷతʹ͸JavaScript؀ڥ΍ɺଞͷ؀ڥ(iOSͳͲ)ʹ΋ରԠ

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Kotlin ͷߟ͑ํ • ݱࡏJava͕࢖ΘΕ͍ͯΔ؀ڥͰɺΑΓੜ࢈ੑ͕ߴ͘ • ΑΓ؆ܿͰ • ΑΓ҆શͰ • Javaͷ୅ସݴޠ

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Kotlin ͷߟ͑ํ • ݱࡏJava͕࢖ΘΕ͍ͯΔ؀ڥͰɺΑΓੜ࢈ੑ͕ߴ͘ → ࣮༻ओٛ • ΑΓ؆ܿͰ • ΑΓ҆શͰ • Javaͷ୅ସݴޠ

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Kotlin ͷߟ͑ํ • ݱࡏJava͕࢖ΘΕ͍ͯΔ؀ڥͰɺΑΓੜ࢈ੑ͕ߴ͘ → ࣮༻ओٛ • ΑΓ؆ܿͰ → ؆ܿ • ΑΓ҆શͰ • Javaͷ୅ସݴޠ

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Kotlin ͷߟ͑ํ • ݱࡏJava͕࢖ΘΕ͍ͯΔ؀ڥͰɺΑΓੜ࢈ੑ͕ߴ͘ → ࣮༻ओٛ • ΑΓ؆ܿͰ → ؆ܿ • ΑΓ҆શͰ → ҆શ • Javaͷ୅ସݴޠ

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Kotlin ͷߟ͑ํ • ݱࡏJava͕࢖ΘΕ͍ͯΔ؀ڥͰɺΑΓੜ࢈ੑ͕ߴ͘ → ࣮༻ओٛ • ΑΓ؆ܿͰ → ؆ܿ • ΑΓ҆શͰ → ҆શ • Javaͷ୅ସݴޠ → ૬ޓӡ༻ੑ

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Kotlin ͷߟ͑ํ • ࣮༻ओٛ • ؆ܿ • ҆શ • ૬ޓӡ༻ੑ

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Kotlin ͷߟ͑ํ • ࣮༻ओٛ • ؆ܿ • ҆શ • ૬ޓӡ༻ੑ

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Kotlin ͷ࣮༻ओٛ • Javaͷߟ͑ํ(ΦϒδΣΫτࢦ޲ͳͲ)͕جຊͦͷ··࢖͑Δ • ৽͍͠ػೳ(Lambda/Nullable etc)΋Ͳ͔͜Ͱฉ͍ͨ͜ͱ͋Δػೳ͹͔Γ • πʔϧ͕ॆ࣮͍ͯ͠Δ

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Kotlin ͷ࣮༻ओٛ • Javaͷߟ͑ํ(ΦϒδΣΫτࢦ޲ͳͲ)͕جຊͦͷ··࢖͑Δ • ৽͍͠ػೳ(Lambda/Nullable etc)΋Ͳ͔͜Ͱฉ͍ͨ͜ͱ͋Δػೳ͹͔Γ • πʔϧ͕ॆ࣮͍ͯ͠Δ

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data class Person(val name: String, val age: Int) fun findTheOldest(people: List): Person { var maxAge = 0 var theOldest: Person? = null for (person in people) { if (person.age > maxAge) { maxAge = person.age theOldest = person } } return theOldest }

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Kotlin ͷ࣮༻ओٛ • Javaͷߟ͑ํ(ΦϒδΣΫτࢦ޲ͳͲ)͕جຊͦͷ··࢖͑Δ • Javaͷॻ͖ํ͕(ଟগҧ͏ͱ͜Ζ͸͋Δʹ͠Ζ)ͦͷ··࢖͑Δ • KotlinͰ௥Ճ͞Εͨؔ਺ܕϓϩάϥϛϯάͷܗͰ΋ॻ͚Δ • ͲͬͪͰॻ͔͘͸։ൃऀ࣍ୈ

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Kotlin ͷؔ਺ܕϓϩάϥϛϯά • ؔ਺Λ஋ͱͯ͠ѻ͑Δ • ϥϜμࣜ • σʔλΫϥε(ෆมͳ஋) • ඪ४ϥΠϒϥϦ಺ͷ๛෋ͳAPI܈(֦ுؔ਺)

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data class Person(val name: String, val age: Int) fun findTheOldest(people: List) = persons.maxBy{ it.age } σʔλΫϥε ϥϜμࣜ ؔ਺ ϥϜμ ΛҾ਺ʹऔΔ֦ுؔ਺ ෆม

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Kotlin ͷ࣮༻ओٛ • Javaͷߟ͑ํ(ΦϒδΣΫτࢦ޲ɾ੩తܕ෇͚)͕جຊͦͷ··࢖͑Δ • ؔ਺ܕϓϩάϥϛϯάͰॻ͘ͱɺศརͳ৔໘(ίϨΫγϣϯͳͲ)͸ଟ͍ • ͲͬͪͰॻ͔͘͸ڧ੍͞Ε͓ͯΒͣ։ൃऀ࣍ୈ

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Kotlin ͷߟ͑ํ • ࣮༻ओٛ • ؆ܿ • ҆શ • ૬ޓӡ༻ੑ

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Kotlin ͷ؆ܿ͞ • ಡΈ΍͢͞Λॏࢹ • ϘΠϥϓϨʔτ(͓ܾ·Γͷίʔυ=ಡ·ͳͯ͘ྑ͍ίʔυ)ΛۃྗݮΒ͢ • Α͋͘Δػೳ͸ඪ४ϥΠϒϥϦͰఏڙ(લड़ͷmaxByͳͲ) • ಡΈʹ͘͘ͳΔ͜ͱ͸ͤ͞ͳ͍(ΧελϜԋࢉࢠͳͲ)

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//Kotlin data class Person(val name: String, val age: Int)

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//Java public final class Person { private final String name; private final int age; public Person(String name, int age) { this.name = name; this.age = age; } public final String getName() { return this.name; } public final int getAge() { return this.age; } public final Person copy(String name, int age) { return new Person(name, age); } public String toString() { return "Person(name=" + this.name + ", age=" + this.age + ")"; } public int hashCode() { return (this.name != null?this.name.hashCode():0) * 31 + this.age; } public boolean equals(Object var1) { //… } }

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Data class ϘΠϥϓϨʔτ(͓ܾ·Γͷίʔυ=ಡ·ͳͯ͘ྑ͍ίʔυ)ΛۃྗݮΒ͢ • ίϯύΠϥͰͷϑΟʔϧυ΁ͷ୅ೖ • getter / setter → ʮϓϩύςΟʯͱ͍͏ߟ͑ํ • copy / toString / hasCode / equals ΛࣗಈͰੜ੒

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Data class ΫϥεΛఆٛ͢Δ্Ͱͷؔ৺ࣄ͸ ʮϓϩύςΟͷܕ͕ԿͰɺ໊લ͕Կ͔ɺͦΕ͕Մม͔ෆม͔ʯ͚ͩ ͦΕҎ֎ͷϘΠϥʔϓϨʔτ͸ίϯύΠϥʹΑͬͯੜ੒͞ΕΔ data class Person(val name: String, val age: Int)

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Kotlinͷ؆ܿ͞ ੩తܕ෇͚ݴޠͰ͋Γɺܕਪ࿦͕ಇ͘ var maxAge = 0 var maxAge : Int = 0

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Kotlinͷ؆ܿ͞ ؔ਺ͷ໭Γ஋ͳͲ΋ܕਪ࿦͕ಇ͘ ؔ਺ͷදݱʹϥϜμ͕࢖͑Δ Α͋͘Δػೳ͸ඪ४ϥΠϒϥϦͰఏڙ fun findTheOldest(people: List) = persons.maxBy{ it.age } fun findTheOldest(people: List) : Person = persons.maxBy({ it.age })

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Kotlin ͷߟ͑ํ • ࣮༻ओٛ • ؆ܿ • ҆શ • ૬ޓӡ༻ੑ

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Kotlin ͷ҆શ͞ • ҆શੑΛߴΊΔ͜ͱͱ࣮૷ίετ͕ߴ͘ͳΔ͜ͱ͸ৗʹτϨʔυΦϑ • ΑΓ௿ίετͰߴ͍҆શੑΛ௥ٻ • ੩తܕ෇͚͸ͦͷ··ʹɺܕਪ࿦ʹΑΓίετΛԼ͍͛ͯΔ

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Kotlin ͷ҆શ͞ • ҆શੑΛߴΊΔ͜ͱͱ࣮૷ίετ͕ߴ͘ͳΔ͜ͱ͸ৗʹτϨʔυΦϑ • ΑΓ௿ίετͰߴ͍҆શੑΛ௥ٻ • ੩తܕ෇͚͸ͦͷ··ʹɺܕਪ࿦ʹΑΓίετΛԼ͍͛ͯΔ • ॏཁͳ2ͭͷΤϥʔΛίετͷΑΓ͔͔Βͳ͍ํ๏Ͱ๷ࢭ • NullPointerException & ClassCastException

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Null҆શ NullPointerException͕ϥϯλΠϜ࣌ʹى͜ΔͷΛ๷͙ Nullڐ༰ܕ(Nullable)ͱɺNullඇڐ༰ܕ(Non-Null)Λ۠ผ ௿ίετ(“?”Ұจࣈ)Ͱ࣮ݱ var theOldest: Person? = null var theOldest: Person = null //Error!

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ClassͷΩϟετ Ұ౓ܕνΣοΫͨ͠ޙͷείʔϓ಺Ͱ͸ɺ࠶౓ͷΩϟετ͸ෆཁ ʮεϚʔτΩϟετʯͱݺ͹ΕΔ if(value is String) { println(value.toUpperCase()) }

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Kotlin ͷߟ͑ํ • ࣮༻ओٛ • ؆ܿ • ҆શ • ૬ޓӡ༻ੑ

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Kotlin ͷ૬ޓӡ༻ੑ • Kotlin͸JavaͷclassϑΝΠϧ΁ͱίϯύΠϧ͞ΕΔ • KotlinͱJavaͷιʔεΛࣗ༝ʹߦ͖དྷͰ͖Δ • JavaͷϥΠϒϥϦΛ࢖͑ΔɺJava͔ΒKotlinͷίʔυΛ࢖͑Δ • Kotlin͸JavaͷطଘͷΫϥε(List΍MapͳͲ)Λ࢖͍ͬͯΔ

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Kotlin ͷߟ͑ํ • ࣮༻ओٛ - Javaͷߟ͑ํ͕ͦͷ··࢖͑Δɻ৽͍͠ػೳ͸طଘͷ΋ͷΛར ༻ɻֶश͕༰қɻ • ؆ܿ - ಡΈ΍͢͞ΛॏࢹɻϘΠϥʔϓϨʔτ͸ۃྗݮΒ͢ɻ • ҆શ - ੩తܕ෇͚ɻNull҆શɻεϚʔτΩϟετɻ • ૬ޓӡ༻ੑ - JavaͱKotlinͷؒ͸ࣗ༝ʹߦ͖དྷɻϥΠϒϥϦ΋طଘͷ΋ͷ Λͦͷ··ར༻Ͱ͖Δɻ

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Kotlin ͷ஫ҙ఺ • Javaͷ୅ସݴޠͰ͋Γ࣮༻ओٛͰ͋ΔͷͰɺࣗ༝౓͕ߴ͍ • ؆ܿʹॻ͖͗͢ΔͱಡΈʹ͘͘ͳΔ͜ͱ΋ • νʔϜ಺ͳͲͰͷίʔσΟϯάϧʔϧ͸߹ͬͨ΄͏͕ྑͦ͞͏

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Kotlinͷݴޠػೳ

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Kotlin ͷݴޠػೳ • ม਺એݴ(val / var) & ܕਪ࿦ • Data classͱϓϩύςΟ • ੍ޚߏจ (if / when / for / when) • Nullڐ༰ܕ / Nullඇڐ༰ܕ • Lambda(ϥϜμ) • ඪ४ϥΠϒϥϦ & ֦ுؔ਺

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ม਺એݴ(val / var) & ܕਪ࿦ ෆม(val) or Մม(var) Ͱ͋Δ͔Λࢦఆͯ͠ม਺Λએݴ ܕ͸ม਺ͷޙΖʹஔ͕͘ܕਪ࿦ग़དྷΔ৔߹͸লུՄೳ ෆม(val) ͸Javaͷﬁnalʹ૬౰͠ɺ࠶୅ೖͰ͖ͳ͍ Մม - mutable ,ෆม - immutable val answer = 42 var answer2 : Int = 42 answer = 4 //Error! answer2 = 4 //OK!

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ม਺એݴ(val / var) & ܕਪ࿦ จ຺తʹҰ౓͔͠ॳظԽ͞Εͳ͍৔߹΋val͕࢖༻Ͱ͖Δ val message: String if (canPerformOperation()) { message = "Success" // ... perform the operation } else { message = "Failed" }

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ม਺એݴ(val / var) & ܕਪ࿦ • Ͱ͖Δ͚ͩෆม(val) Λ࢖͍ɺඞཁͳ࣌ʹ͚ͩՄม(var)ʹ͢Δ • ActivityͷϑΟʔϧυͳͲɺvalʹ͠ਏ͍৔ॴ΋͋Γ·͕͢ɺ஗ԆॳظԽ (lazy)ͳͲΛ࢖͑͹ՄೳʹͳΔ৔໘΋͋Δ • ܕ͸໌ࣔͯ͠΋ܕਪ࿦ʹ·͔ͤͯ΋ྑ͍

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Data class ίϯύΠϥͰͷϑΟʔϧυ΁ͷ୅ೖ getter / setter → ʮϓϩύςΟʯͱ͍͏ߟ͑ํ copy / toString / hasCode / equals ΛࣗಈͰੜ੒ data class Person(val name: String, var isMarried: Boolean)

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௨ৗͷclass ίϯύΠϥͰͷϑΟʔϧυ΁ͷ୅ೖ getter / setter → ʮϓϩύςΟʯͱ͍͏ߟ͑ํ class Person(val name: String, var isMarried: Boolean)

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௨ৗͷclass ίϯύΠϥͰͷϑΟʔϧυ΁ͷ୅ೖ getter / setter → ʮϓϩύςΟʯͱ͍͏ߟ͑ํ class Person(val name: String, var isMarried: Boolean)

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//Kotlin data class Person(val name: String, var isMarried: Boolean) //Kotlin >>> val person = Person("Bob", true) >>> println(person.name) Bob >>> println(person.isMarried) true

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//Kotlin data class Person(val name: String, var isMarried: Boolean) //Java >>> Person person = new Person("Bob", true); >>> System.out.println(person.getName()); Bob >>> System.out.println(person.isMarried()); true

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//Kotlin data class Person(val name: String, var isMarried: Boolean) //Kotlin >>> val person = Person("Bob", true) >>> println(person.name) Bob >>> println(person.isMarried) true person.name = "Alice" //Error! person.isMarried = false //OK!

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ϓϩύςΟ • JavaͷϑΟʔϧυͱΞΫηαϝιου(setter/getter)Λஔ͖׵͑Δ΋ͷ • val nameͱએݴ͢ΔͱKotlin͔Β͸nameɺJava͔Β͸getNameͱͯ͠ ݟ͑Δ • ܕ͕Booleanͷ৔߹͸ྫ֎ͱͯ͠isͰ࢝·Δؔ਺ʹͳΔ • varͰએݴ͢Ε͹setter͕͋ΓɺvalͰએݴͨ͠৔߹͸setter͕ͳ͍

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Kotlin ͷݴޠػೳ • ม਺એݴ(val / var) & ܕਪ࿦ • Data classͱϓϩύςΟ • ੍ޚߏจ (if / when / for / while) • Nullڐ༰ܕ / Nullඇڐ༰ܕ • Lambda(ϥϜμ) • ඪ४ϥΠϒϥϦ & ֦ுؔ਺

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੍ޚߏจ • if - Javaͱ΄΅ಉ͡ • when - JavaͷswitchΛڧྗʹͨ͠΋ͷ(Kotlinʹswitchจ͸ແ͍) • for - Javaͷfor-each(‘for (String item : list )’ͳͲ)͔͠ͳ͍ • while - Javaͱશ͘ಉ͡

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ifจ KotlinͰ͸ifจΛࣜͱͯ͠ѻ͍ɺ஋Λฦ͢͜ͱ͕ग़དྷΔ Javaͷࡾ߲ԋࢉࢠ͸Kotlinʹ͸ແ͍ val larger = if(a > b) a else b

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ifจ தׅހΛ࢖͏৔߹͸ɺͦͷதͷ࠷ޙͷจΛif͕ฦ͢஋ͱͯ͠ѻ͏ ifҎ֎ʹɺwhen΍try-catch΋ಉ༷ʹ஋Λฦࣜ͢ͱͯ͠ѻ͑Δ val result : String = if(isSuccess()){ // do something "Success" } else { "Failure" }

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whenจ ڧྗͳswitchจ Javaͱҧ͍ɺϓϦϛςΟϒܕɺenumܕҎ֎ʹ΋࢖͑Δ fun getColorName(color: Color) = when (color) { Color.RED -> "Red" Color.ORANGE -> "Orange" Color.YELLOW -> "Yellow" else -> "Unknown" }

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whenจ ৚݅ʹෳ਺ͷ߲໨ΛೖΕΔ͜ͱ͕Մೳ fun getWarmth(color: Color) = when (color) { RED, ORANGE, YELLOW -> "warm" GREEN -> "neutral" BLUE, INDIGO, VIOLET -> "cold" }

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whenจ whenΛҾ਺ͳ͠Ͱ࢖͏͜ͱ΋ग़དྷΔ when { x.isOdd() -> print("x is odd") x.isEven() -> print("x is even") else -> print("x is funny") }

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forจ inΛ࢖ͬͯɺJavaͷfor-eachจͷΑ͏ͳ܁Γฦ͠ॲཧ͕ग़དྷΔ Collection΍MapΛinͷޙΖʹஔ͘͜ͱ͕ग़དྷΔ for (item in collection) print(item) for (i in 1..100) { print(fizzBuzz(i)) }

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forจ downTo΍stepΛ࢖ͬͯɺൣғΛࢦఆ͢Δ͜ͱ΋ग़དྷΔ for (i in 100 downTo 1 step 2) { print(fizzBuzz(i)) }

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Nullڐ༰ܕ / Nullඇڐ༰ܕ Nullڐ༰ܕ(Nullable)ͱɺNullඇڐ༰ܕ(Non-Null)Λ۠ผ ௨ৗͷܕ͸Nullඇڐ༰ܕɺͦΕʹʹ?͕͍ͭͨ΋ͷ͕Nullڐ༰ܕ ϓϦϛςΟϒܕʹ΋nullڐ༰ܕ͕͋Δ var a: String = "" var b: String? = null var c: Int? = null

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Nullඇڐ༰ܕ Nullඇڐ༰ܕ͸͜Ε·Ͱ௨ΓϓϩύςΟࢀরɺϝιουݺͼग़͕͠ग़དྷΔ Nullඇڐ༰ܕͷม਺ʹnullΛ୅ೖ͢ΔͱίϯύΠϧΤϥʔͱͳΔ fun strLength(str : String) = str.length strLength(null) // Error!

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Nullڐ༰ܕ Nullڐ༰ܕ͸ϓϩύςΟࢀরɺϝιουݺͼग़͕͠ίϯύΠϧΤϥʔͱͳ Δ → ϓϩύςΟࢀরɺϝιουݺͼग़࣌͠͸ಛผͳํ๏͕ඞཁ Nullڐ༰ܕʹ͸nullΛ୅ೖ͢Δ͜ͱ͕ग़དྷΔ fun strLength(str : String?) = str.length //Error! strLength(null) //OK!

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Nullڐ༰ܕ / Nullඇڐ༰ܕ • Ͱ͖Δ͚ͩNullඇڐ༰ܕ(Non-Null)Ͱఆٛ͢Δ • ඞཁͳ৔໘͚ͩʹNullڐ༰ܕ(Nullable)Λ࢖͏ • Nullڐ༰ܕ͸ಛผʹѻ͏ඞཁ͕͋Δ • Kotlin಺Ͱ͸ඞͣͲͪΒ͔ͷܕʹͳΔ͕ɺϓϥοτϑΥʔϜܕ(ܕ໊ͷޙΖʹ!)ͱ͍ ͏Java͔Β΍ͬͯ͘Δಛผͳܕ͕͋Δ • ίϯύΠϧޙ͸Javaͷ௨ৗͷܕͱಉ༷ʹѻΘΕΔͷͰϥϯλΠϜ࣌ͷΦʔόʔϔο υ͸ͳ͍

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Nullඇڐ༰ܕͷѻ͍ํ • ifจʹΑΔnullνΣοΫ • ҆શݺͼग़͠ (?.) • ΤϧϏεԋࢉࢠ(?:) • ඇNullද໌(!!)

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ifจʹΑΔnullνΣοΫ ifจͰҰ౓ɺnullͰͳ͍͜ͱΛνΣοΫ͢ΔͱnullʹͳΓಘͳ͍จ຺ͷதͰ ͸ɺNullඇڐ༰ܕͱͯ͠ѻ͑Δ ࢓૊Έతʹ͸εϚʔτΩϟετ fun strLength(str : String?) : Int = if (str != null) { str.length } else { 0 }

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҆શݺͼग़͠(?.) Nullڐ༰ܕʹ?.Λ͚ͭΕ͹ɺϓϩύςΟ΍ϝιουΛ҆શʹݺͼग़ͤΔ ม਺͕nullͷ৔߹͸ݺͼग़͕࣮͠ߦ͞ΕͣɺnullΛฦ͢ νΣΠϯͤ͞Δ͜ͱ΋ग़དྷΔ fun strLength(str : String?) : Int? = str?.length >>> println(strLength("abc")) 3 >>> println(strLength(null)) null /VMMڐ༰ܕ

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ΤϧϏεԋࢉࢠ(?:) ԋࢉࢠ(?:)ͷલ͕nullͳΒޙΖͷ஋Λฦ͢ ΤϧϏεɾϓϨεϦʔ໊͕લͷ༝དྷ fun strLength(str : String?) : Int = str?.length ?: 0 >>> println(strLength("abc")) 3 >>> println(strLength(null)) 0 /VMMඇڐ༰ܕ

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ඇNullද໌(!!) Nullڐ༰ܕΛNullඇڐ༰ܕʹڧ੍తʹม׵͢Δ ΋͠null͕ೖͬͯͨ৔߹͸ϥϯλΠϜ࣌ʹNullPointerException͕౤͛ΒΕ Δ fun strLength(str : String?) : Int = str!!.length >>> println(strLength("abc")) 3 >>> println(strLength(null)) // NullPointerException /VMMඇڐ༰ܕ

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Nullඇڐ༰ܕͷѻ͍ํ • ඇNullද໌(!!)͸ۃྗ࢖ΘͣʹɺԼͷ3ͭΛ৔໘ʹԠͯ͡࢖͍෼͚Δ • ifจʹΑΔnullνΣοΫ • ҆શݺͼग़͠ (?.) • ΤϧϏεԋࢉࢠ(?:) • ҆શݺͼग़͠ʹείʔϓؔ਺Λ૊Έ߹Θͤͯ࢖͏ํ๏΋͋Δ

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είʔϓؔ਺ͱNullڐ༰ܕ είʔϓؔ਺ʹ͸ let / apply / with / run / also ͕͋Δ Nullඇڐ༰ܕΛҾ਺ʹͱΔؔ਺Λݺͼग़࣌͢ʹศར ϥϜμ(ޙड़)ͱ૊Έ߹Θͤͯ࢖͏ fun sendEmailTo(email: String) { /*...*/ } val email: String? = ... sendEmailTo(email) //Error! email?.let { sendEmailTo(it) } //OK! /VMMඇڐ༰ܕ

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Lambda(ϥϜμ) ஋ͱͯ͠ѻ͑Δؔ਺ ߴ֊ؔ਺ͷҾ਺ʹͳΓಘΔ persons.maxBy { it.age } fun > Iterable.maxBy(selector: (T) -> R): T? Ҿ਺͕ؔ਺ܕ

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LambdaͷҾ਺ͷলུ ϥϜμͷҾ਺Λলུͤͣʹॻ͘͜ͱ΋ग़དྷΔ it͸ϥϜμͷҾ਺͕1ͭͰɺҾ਺ͷఆٛΛলུͨ͠৔߹ʹͷΈ࢖͑Δ persons.maxBy { it.age } persons.maxBy { p:Person -> p.age }

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LambdaΛҾ਺ʹऔΔ৔߹ͷ()ͷলུ ϥϜμ͕Ҿ਺ͷ࠷ޙʹ͋Δ৔߹ɺͦΕΛ()ͷ֎ʹग़͢͜ͱ͕ग़དྷΔ ϥϜμ͕།ҰͷҾ਺ͷ৔߹ɺ()Λলུ͢Δ͜ͱ͕ग़དྷΔ persons.maxBy { it.age } persons.maxBy(){ it.age } persons.maxBy({ it.age }) persons.maxBy(){ p:Person -> p.age } persons.maxBy({ p:Person -> p.age })

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SAMม׵ ϥϜμ͸Javaͷಗ໊Ϋϥεͷ୅ΘΓʹ΋࢖͏͜ͱ͕ग़དྷΔ ͨͩͦ͠ͷΠϯλϑΣʔε͕1͔ͭ͠ந৅ϝιουΛ࣋ͨͳ͍৔߹ʹݶΔ SAMม׵(Single Abstract Method)ͱݺ͹ΕΔ //Java button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { /* actions on click */ } }); //Kotlin button.setOnClickListener { /* actions on click */ }

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Kotlinͷඪ४ϥΠϒϥϦ είʔϓؔ਺΍ίϨΫγϣϯૢ࡞(maxBy΋ͦͷ1ͭ)ͳͲͷศརͳؔ਺܈͕ ఏڙ͞Ε͍ͯΔ αΠζ͕খ͍͞ͷͰAndroidͷapkʹؚΊͯ΋໰୊ͳ͍ ଟ͕֦͘ுؔ਺ fun > Iterable.maxBy(selector: (T) -> R): T?

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֦ுؔ਺ Ϋϥε֎͔ΒΫϥεʹؔ਺Λ௥Ճ͢Δ͜ͱ͕ग़དྷΔ ֦ுͨ͠ΫϥεΛϨγʔόܕͱݺͿ fun String.toInt(): Int = java.lang.Integer.parseInt(this) val i = "120".toInt() ֦ுର৅ͷΫϥε UIJT͸֦ுͨ͠Ϋϥε ͷΦϒδΣΫτ

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঺հͨ͠Kotlin ͷݴޠػೳ • ม਺એݴ(val / var) & ܕਪ࿦ • Data classͱϓϩύςΟ • ੍ޚߏจ (if / when / for / when) • Nullڐ༰ܕ / Nullඇڐ༰ܕ • Lambda(ϥϜμ) • ඪ४ϥΠϒϥϦ & ֦ுؔ਺

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Kotlin ͷݴޠػೳ • Kotlinͷݴޠػೳ͸ɺଞʹ΋ͨ͘͞Μ͋Δ • Kotlin͸࣮༻ओٛͰɺ؆ܿͰɺ҆શͰɺJavaͱͷ૬ޓӡ༻ੑΛॏࢹͨ͠ ݴޠ • ·ͣ͸ɺ҆શੑ(Null҆શ)ʹҙࣝ͠ͳ͕Βॻ͖࢝Ίͯɺঃʑʹ༷ʑͳػ ೳΛ࢖͍࢝ΊΔͱྑ͍

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Kotlinͷπʔϧ

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Kotlin Λ࢝ΊΔͨΊͷπʔϧ • Android Studio • Convert Java to Kotlin

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Android Studio • 3.0Ҏ߱ͰKotlinͷPlugin͕σϑΥϧτͰೖͬͨ • ͦΕҎલͷόʔδϣϯͰ΋PluginΛೖΕΔ͜ͱͰKotlinͰͷ։ൃ͕Մೳ

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Android Studio 3.0 ϓϩδΣΫτ։࢝࣌ʹKotlinͰ࢝ΊΔ͜ͱ͕ग़དྷΔ

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buid.gradle buildscript { ext.kotlin_version = '1.1.3-2' dependencies { classpath 'com.android.tools.build:gradle:3.0.0-beta3' classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" } } app/build.gradle apply plugin: ‘kotlin-android' dependencies { compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version" }

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Kotlin with Android Studio • Ͳͷબ୒ࢶͰ΋Մೳ • ϓϩδΣΫτ։࢝࣌ʹKotlin supportΛબͿ • Tools>Kotlin>Conﬁgure Kotlin in ProjectΛ࢖ͬͯKotlinϓϩδΣΫτԽ • खॻ͖ͰKotlinͷઃఆΛgradleʹ௥Ճ

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Convert Java to Kotlin • JavaͷϑΝΠϧΛબ୒ͯ͠ʮCodeʯϝχϡʔ͔ ΒʮConvert Java File to Kotlin FileʯΛબͿ͜ͱ Ͱίʔυ͕Kotlinʹม׵͞ΕΔ • JavaͷίʔυΛKotlinͷϑΝΠϧ(.kt)΁ίϐϖ͢ Δ͜ͱͰ΋Kotlinʹม׵͞ΕΔ

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Convert Java to Kotlin • Kotlinͷֶशʹศར • ͨͩ͠ɺྑ͍ίʔυͱ͸ݶΒͳ͍ͷͰཁ஫ҙ • ಛʹnull҆શʹ͸ؾΛ഑Δ

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ຊ೔ͷGoal • ʮKotlin ͱ͸Կͩʁʯˠ Kotlinͷߟ͑ํʹ͍ͭͯ஌Δ • ʮͳΜͰ Kotlinͳͷ͔ʁʯˠ KotlinͷݴޠػೳΛ஌Δ • ʮͲ͏΍ֶͬͯ΂͸ྑ͍ͷ͔ʁʯˠ KotlinΛ࢝ΊΔͨΊͷπʔϧΛ஌Δ

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·ͱΊ • Kotlin͸࣮༻ओٛͰɺ؆ܿͰ҆શͳɺJavaͱͷ૬ޓӡ༻ੑ͕ߴ͍ݴޠ • ্هΏ͑ʹॻ͖ํͷࣗ༝౓͕ߴ͍ݴޠ • ༷ʑͳػೳ͕༻ҙ͞Ε͍ͯΔͷ΋Kotlinͷಛ௃ • ·ͣ͸Null҆શΛҙࣝ͠ͳ͕Βॻ͖࢝ΊΔ • ಋೖ͢Δ৔߹͸νʔϜ಺Ͱͷٞ࿦͸ඞਢ(ֶशظؒઃ͚Δͷ΋ྑ͍)

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How to start Kotlin • Ofﬁcial Site : kotl.in/ , kotl.in/android • Kotlin is awesome! (kotlin.link/) • Kotlin in Action • Kotlin ελʔτϒοΫ(੺΂͜ຊ) • Kotlin Advent Calendar (2015/2016) • Kotlinೖ໳·Ͱͷॿ૸ಡຊ( goo.gl/5vUT7o )

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Thank you ! Let’s enjoy Kotlin