Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
忙しい人のための Functional Programming in Java / Funct...
Search
Youhei Nitta
November 14, 2014
Programming
0
930
忙しい人のための Functional Programming in Java / Functional Programming in Java for business person
社内勉強会でサンプルコードをベースに「Javaによる関数型プログラミング」の簡単なふりかえりをしました.
喋りで補ったところが多いかも...
Youhei Nitta
November 14, 2014
Tweet
Share
More Decks by Youhei Nitta
See All by Youhei Nitta
実践 Git / Pragmatic Git
youhei
2
180
Other Decks in Programming
See All in Programming
『毎日の移動』を支えるGoバックエンド内製開発
yutautsugi
2
180
CSC305 Lecture 01
javiergs
PRO
1
400
デミカツ切り抜きで面倒くさいことはPythonにやらせよう
aokswork3
0
190
Pythonスレッドとは結局何なのか? CPython実装から見るNoGIL時代の変化
curekoshimizu
4
1.3k
Back to the Future: Let me tell you about the ACP protocol
terhechte
0
130
どの様にAIエージェントと 協業すべきだったのか?
takefumiyoshii
2
600
そのpreloadは必要?見過ごされたpreloadが技術的負債として爆発した日
mugitti9
2
3k
Чего вы не знали о строках в Python – Василий Рябов, PythoNN
sobolevn
0
160
階層構造を表現するデータ構造とリファクタリング 〜1年で10倍成長したプロダクトの変化と課題〜
yuhisatoxxx
3
910
プログラミングどうやる? ~テスト駆動開発から学ぶ達人の型~
a_okui
0
190
Let's Write a Train Tracking Algorithm
twocentstudios
0
220
AIエージェント時代における TypeScriptスキーマ駆動開発の新たな役割
bicstone
4
1.5k
Featured
See All Featured
Rebuilding a faster, lazier Slack
samanthasiow
84
9.2k
Bash Introduction
62gerente
615
210k
個人開発の失敗を避けるイケてる考え方 / tips for indie hackers
panda_program
114
20k
JavaScript: Past, Present, and Future - NDC Porto 2020
reverentgeek
52
5.6k
実際に使うSQLの書き方 徹底解説 / pgcon21j-tutorial
soudai
PRO
188
55k
The Web Performance Landscape in 2024 [PerfNow 2024]
tammyeverts
9
850
Large-scale JavaScript Application Architecture
addyosmani
514
110k
GitHub's CSS Performance
jonrohan
1032
460k
Optimising Largest Contentful Paint
csswizardry
37
3.4k
How STYLIGHT went responsive
nonsquared
100
5.8k
Improving Core Web Vitals using Speculation Rules API
sergeychernyshev
19
1.2k
Designing for humans not robots
tammielis
254
25k
Transcript
@youhei Software Engineer Fri Nov 14 © 2014 Youhei Nitta,
All rights reserved. Redistribution or public display not permitted without written permission from Youhei Nitta. ͍͠ਓͷͨΊͷ Functional Programming in Java
Java ʹΑΔؔܕϓϩάϥϛϯά Java 8 ϥϜμࣜͱ Stream ಡΈ·ͨ͠ɻ ྑॻͩͬͨͷͰɺखʹৼΓ ฦͬͯΈ·͢ɻ
ैདྷͷํ๏ public static void main(final String[] args) {! BigDecimal totalOfDiscountedPrices
= BigDecimal.ZERO;! ! for(BigDecimal price : prices) {! if(price.compareTo(BigDecimal.valueOf(20)) > 0) ! totalOfDiscountedPrices = ! totalOfDiscountedPrices.add(price.multiply(BigDecimal.valueOf(0.9)));! }! System.out.println("Total of discounted prices: " + totalOfDiscountedPrices);! } ໋ྩܕελΠϧ ͲͷΑ͏ʹ࣮ߦͯ͠ཉ͍͔͠Λهड़ mutable ͳมΛѻ͍ͬͯΔ
Java 8 public static void main(final String[] args) {! final
BigDecimal totalOfDiscountedPrices = ! prices.stream()! .filter(price -> price.compareTo(BigDecimal.valueOf(20)) > 0)! .map(price -> price.multiply(BigDecimal.valueOf(0.9)))! .reduce(BigDecimal.ZERO, BigDecimal::add);! ! System.out.println("Total of discounted prices: " + totalOfDiscountedPrices);! } ؔܕελΠϧ ྲྀΕΔΑ͏ʹॲཧΛॻ͘ (Stream API) ԿΛ࣮ߦ͖͔͢Λهड़ ࠶ೖΛճආ͍ͯ͠Δ
ͳͥؔܕΛ͏ͷ͔ • એݴతͰಡΈ͍͢ • ෆมੑʹΑΓόάΛࠞೖ͠ʹ͍͘ • ฒྻԽ͕༰қ • ԆධՁʹΑΓޮత
Java 8 ϥϜμࣜ
Java 8 ͷϥϜμࣜͷϙΠϯτ ୯ҰϝιουΠϯλϑΣʔε (Comparable, Runnable ͳͲ) ͷಗ໊ΫϥεͷΠϯελϯεΛ͢ɺͱ͍͏ݩʑ ͋ͬͨίϯηϓτΛ֦ுͨ͠ɻ ܰྔͳه๏ͱͯ͠ϥϜμࣜΛಋೖ͠ɺ͔͋ͨؔΛ
͍ͯ͠ΔΑ͏ʹݟͤͯɺ࣮୯Ұϝιουಗ໊Ϋϥεͷ ΠϯελϯεΛ͍ͯ͠Δɻ طଘͷ JDK ϥΠϒϥϦʹޓੑΛͭͷ͕རɻ
ಗ໊ΫϥεͷΠϯελϯε friends.forEach(new Consumer<String>() {! public void accept(final String name) {!
System.out.println(name);! }! }); Java 7 Ҏલͷจ๏ʹԊͬͨه๏ɻ Iterable ͷ forEach ϝιουʹ Consumer ಗ໊Ϋϥεͷ ΠϯελϯεΛ͍ͯ͠Δɻ
ϥϜμࣜ ! //ॲཧ͕1ߦͩͱίʔυϒϩοΫͷׅހলུՄɻҾʹ final Λ໌ࣔͰ͖Δɻ! friends.forEach((final String name) -> System.out.println(name));!
//ܕਪͰҾͷܕએݴΛলུՄɻ! friends.forEach((name) -> System.out.println(name));! //Ҿ͕1ݸͩͱׅހΛলུՄɻ! friends.forEach(name -> System.out.println(name)); ϥϜμࣜҥߏจɻ ίϯύΠϥ͕߹ϝιουΛੜ͍ͯ͠Δɻ ※ ࣮ґଘ͕ͩಗ໊ΫϥεͷΠϯελϯεੜͷҥߏจͰͳ͘ɺinvokedynamic Ͱ࣮ߦ࣌ʹಗ໊ΫϥεΛੜ͢Δॲཧʹஔ͖ΘΔɻΫϥεϑΝΠϧΛ࡞Βͤͳ͍ͨΊɻ
ϝιουࢀর //Ҿলུ! friends.forEach(System.out::println); ϝιουͷ໊લΛ͢ͷͰՄಡੑ͕ߴ͍ɻ ϝιουࢀরҾΛิ͠ίϯύΠϥ͕߹ϝιουʹ ม͍ͯ͠Δɻ
࣮ࡍʹͬͯΈͯ ଞͷݴޠͷϥϜμࣜͱ༻ײ͕ҧͬͨɻ API Λఏڙ͢Δଆ͔ΒΈͯҧ͍͕ͳ͍ɻ ! API ར༻ଆͷࢹ: ؔʢϥϜμࣜɾϝιουࢀরʣΛҾʹ͍ͯ͠Δ ! API
ఏڙଆͷࢹ: Ҿʹ͜Ε·Ͱ௨ΓͷΠϯελϯεΛड͚औ͍ͬͯΔ
Strategy Pattern
Predicate<T> ͰϩδοΫΛ͚Δ ! public static int totalAssetValues(final List<Asset> assets,! final
Predicate<Asset> assetSelector) {! return assets.stream()! .filter(assetSelector)! .mapToInt(Asset::getValue)! .sum();! }! ! //! totalAssetValues(assets, asset -> true);! totalAssetValues(assets, asset -> asset.getType() == AssetType.BOND));! totalAssetValues(assets, asset -> asset.getType() == AssetType.STOCK));! Strategy Pattern ͰϩδοΫΛൈ͖ग़͍ͯ͠Δɻ ࠓ·Ͱ৽͍͠ΫϥεΛ༻ҙ͍͕ͯͨ͠ɺϥϜμࣜͰදݱͰ͖ΔΑ͏ʹͳͬͨɻ ؔܕʹ׳Ε͍ͯΔͱී௨ͷύλʔϯ͚ͩͲɺJava Ͱॻ͚ΔΑ͏ʹͳͬͨɻ
Decorator Pattern
Stream API Ͱ࣍ʑʹద༻͢Δ public class Camera { ! private Function<Color,
Color> filter;! ! public void setFilters(final Function<Color, Color>... filters) {! filter = ! Stream.of(filters)! .reduce((filter, next) -> filter.compose(next))! .orElse(color -> color);! //.orElseGet(Function::identity); Ͱಉ͡! }! }! ! camera.setFilters(Color::brighter);! camera.setFilters(Color::darker);! camera.setFilters(Color::brighter, Color::darker); Decorator ύλʔϯɻΫϥεΛೖΕࢠʹͤͣ Stream API Ͱద༻ͨ݁͠ՌΛฦ͢ɻ ΫϥεΛఆٛͯ͠ೖΕࢠʹ͢Δख͕ؒল͚Δɻ දྫ. new BufferedReader(new InputStreamReader(is, "UTF-8"));
Execute Around Method Pattern
try-finally ͷϦιʔεղ์ public static void main(final String[] args) throws IOException
{! final FileWriterExample writerExample = ! new FileWriterExample("peekaboo.txt");! try {! writerExample.writeStuff("peek-a-boo"); ! } finally {! writerExample.close(); ! }! } యܕతͳύλʔϯ͕ͩɺίʔυ͕ࡶʹͳΔɻ ྫ֎ॲཧΛͪΌΜͱΔͱߋʹɻɻ
try-with-resources ͷϦιʔεཧ public static void main(final String[] args) throws IOException
{! try(final FileWriterARM writerARM = new FileWriterARM("peekaboo.txt")) {! writerARM.writeStuff("peek-a-boo");! ! ! System.out.println("done with the resource...");! }! } Java 7 ͔Βಋೖ͞Εͨɻ AutoCloseable ࣮ΫϥεͰ͋Δඞཁ͕͋Δɻ ։ൃऀ͕ AutoCloseable ͷ࣮Λ࣮֬ʹߦ͍ɺtry-with-resources ΛΕͣʹΘ ͳ͍ͱ͍͚ͳ͍ɻ
Execute Around Method Pattern public static void use(final String fileName,
! // UseInstance accept(T instance) throws X; Λͭ FunctionalInterface! final UseInstance<FileWriterEAM, IOException> block) throws IOException {! ! final FileWriterEAM writerEAM = new FileWriterEAM(fileName); ! try {! block.accept(writerEAM);! } finally {! writerEAM.close();! }! }! ! public static void main(final String[] args) throws IOException {! ! FileWriterEAM.use("eam2.txt", writerEAM -> {! writerEAM.writeStuff("how");! writerEAM.writeStuff("sweet"); ! });! }! } ϥϜμࣜΛ͏ɻ API Λ༻͢ΔਓʹϦιʔεཧΛҙࣝͤ͞ͳ͍ɻ JDBC ͷτϥϯβΫγϣϯཧɺLock ͷཧʹԠ༻Ͱ͖Δɻ
Virtual Proxy Pattern
ॳظԽͷԆ public class HolderNaive {! private Heavy heavy;! ! public
Heavy getHeavy() {! if(heavy == null) {! heavy = new Heavy();! }! ! return heavy;! }! }! ͓ͳ͡Έͷॲཧ͚ͩͲɺ৭ʑରॲ͖͕͋͢Δɻ
εϨουηʔϑ public class HolderThreadSafe {! private Heavy heavy;! ! public
synchronized Heavy getHeavy() {! if(heavy == null) {! heavy = new Heavy();! }! ! return heavy;! }! ! } ڝ߹ঢ়ଶΛഉআͨ͠ɻ εϨουͷ༗ແʹؔΘΒͣϝϞϦόϦΞΛ͑ͳ͚Ε͍͚ͳ͍ɻ ڝ߹͕ʹͳΔͷ࠷ॳ͚ͩɻ
Virtual Proxy Pattern ! public class Holder {! private Supplier<Heavy>
heavy = () -> createAndCacheHeavy();! ! public Heavy getHeavy() {! return heavy.get();! }! ! ϥϜμࣜͷϑΝΫτϦʔΫϥεΛఆٛͯ͠ɺ࠷ॳ͚ͩڝ߹ঢ়ଶʹରॲ͍ͯ͠Δɻ ೋճҎ߱ϑΝΫτϦʔΫϥεΛࠩ͠ସ͑ͯ synchronized ௨Βͣ୯७ʹΠϯελ ϯεΛฦ͢ɻैདྷ͋ͬͨ null νΣοΫͳ͘ͳͬͨɻ private synchronized Heavy createAndCacheHeavy() {! class HeavyFactory implements Supplier<Heavy> {! private final Heavy heavyInstance = new Heavy();! ! public Heavy get() { return heavyInstance; }! }! ! if(!HeavyFactory.class.isInstance(heavy)) {! heavy = new HeavyFactory();! }! ! return heavy.get();! }! ! }
Conclusion
Java ʹΑΔؔܕϓϩάϥϛϯά Java 8 ϥϜμࣜͱ Stream ଞʹϥϜμࣜͷ͑ΔςΫχοΫ͕ͨ͘͞ Μࡌ͍ͬͯ·͢ʢແݶϦετɺ࠶ؼݺͼग़͠ ࠷దԽͳͲʣɻ ࠓճ
Stream API ʹ͍ͭͯେ෯ʹলུͯ͠ ͍·͕͢ɺͦͪΒ͔ͬ͠Γ͓͍͑ͯ͞·͢ɻ ! ʮ࣌ Java!ʯͳͷͰങ͍!!