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5分で分かるかもしれないjava8 Stream API
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Kazuhiro Serizawa
November 26, 2015
Programming
1
2.3k
5分で分かるかもしれないjava8 Stream API
Kazuhiro Serizawa
November 26, 2015
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Transcript
5Ͱ͔Δ͔͠Εͳ͍ java8 Stream API
java8ʹ͍ͭͯ • 20143݄18ʹOracle͔Βެ։ • “ੈքҰͷ։ൃϓϥοτϑΥʔϜͷըظతͳϦϦʔ ε” ※OracleେຊӦൃද • ϥϜμࣜɺStreamAPIɺDate and
Time APIͳͲͷ ৽ػೳͷಋೖͰjavaքʹֵ໋͕ʂ ʢͱࢥ͚ͬͨͲͦ͜·ͰΓ্͕Βͳ͔ͬͨʣ
ࠓ͔̑͠ͳ͍ͷͰ • Stream APIʹ͍ͭͯ֓ཁΛ͠·͢ • ʮjavaগ͠ϚγʹͳͬͨΑ͏ͩͳʯ ͱ͍͏ͷΛײ͡औͬͯΒ͑Ε͍Ͱ͢
Stream APIͱʁ • ྻɺϦετͳͲͷෳͷσʔλʹ͓͚Δू ૢ࡞ͷαϙʔτΛߦ͏API • ฒߦॲཧΒͷϕϯϦػೳΛఏڙͯ͘͠ΕΔ UtilͰͳ͘Interface͚ͩΛఏڙ͢Δ
Stream APIͱʁ • ཁ͢ΔʹRubyͰݴ͏ͱ͜Ζͷ • Enumerable#each • Enumerable#select • Enumerable#map
• ͜ΕΒͷॲཧΛʮܾ·ͬͨखॱͰ࣮ߦ͢ΔʯAPI • Stream API ≠࣮ɻInterfaceͷΈΛఆ͍ٛͯ͠Δɻ
StreamΛΘͳ͍߹ͷྫ List<Integer> list = Arrays.asList(1,2,3); Integer result = 0; for
(Integer i : list) { result += i * i; } System.out.println(result); //14
ͳ͓ruby result = [1,2,3] .map{ |i| i*i } .inject{ |a,b|
a + b } puts result #=> 14
StreamΛ͏߹ͷྫ List<Integer> list = Arrays.asList(1,2,3); Integer result = list.stream() .map(x
-> x * x) .reduce((a, b) -> a + b) .get(); System.out.println(result); //14
Stream APIΛ༻͍࣮ͨ "SSBZ -JTUͳͲͷ %BUBTPVSDF TUSFBN࡞ தؒૢ࡞ ϑΟϧλϦϯάɾͷૢ࡞ͳͲ ऴૢ࡞ ूૢ࡞ɾผΫϥεͷมɾ
ஞ࣍ॲཧͳͲ ॲཧ͞Εͨ݁Ռ list.stream() .map(x -> x * x) .reduce((a, b) -> a + b) .get();
ඪ४ϥΠϒϥϦ with Stream Stream<String> lines = Files.lines(path) lines.filter(line -> line.startsWith(“a”))
.map(s -> s.toUpperCase) .forEach(s -> System.out.println(s)); // “AMAZON” // “ATOM”
StreamʹΑͬͯԿ͕͏Ε͍͔͠ • σʔλϦιʔεૢ࡞ͷ࣮ͷ؆ུԽ • ϥϜμࣜͱΈ߹ΘͤΔ͜ͱͰ ؔܕͬΆ͍syntaxʹ • σʔλϦιʔεʹର͢Δฒߦॲཧɾࢄॲཧ Λstream()ϝιουʹӅṭԽ࣮ͯ͠Ͱ͖Δ
Collection frameworkͩͱ ϚϧνεϨουͰฒߦॲཧ͢ΔstreamΛ࡞ΕΔ List<Integer> list = Arrays.asList(1,2,3); Integer result =
list.parallelStream() .map(x -> x * x) .reduce((a, b) -> a + b) .get(); System.out.println(result); //14
༨ஊɿ Apache SparkΛͬͨࢄॲཧ࣮ input. flatMap(line -> Arrays.asList(line.split("\\s+"))) .mapToPair(word -> new
Tuple2(word, 1)) .reduceByKey((x, y) -> (Integer) x + (Integer) y) .sortByKey() .collect();
Stream APIͷ·ͱΊ • ීஈྑ͘͏Collection Frameworkͷॲཧ͕ γϯϓϧʹ࣮Ͱ͖ΔΑ͏ʹͳΔ • rubyʹ༏͍͠ • ࢄɾฒߦॲཧΛӅṭԽ࣮ͯ͠Ͱ͖ͦ͏ͳ
ઃܭํΛ͍ࣔͯ͠Δ