{"id":3397,"date":"2013-03-15T14:45:44","date_gmt":"2013-03-15T05:45:44","guid":{"rendered":"http:\/\/lab.synergy-marketing.co.jp\/blog\/?p=3397"},"modified":"2018-11-14T16:33:55","modified_gmt":"2018-11-14T07:33:55","slug":"try-using-java-8-lambda","status":"publish","type":"post","link":"https:\/\/www.techscore.com\/blog\/2013\/03\/15\/try-using-java-8-lambda\/","title":{"rendered":"Java 8 \u306e lambda \u3092\u8a66\u3057\u3066\u307f\u307e\u3057\u305f"},"content":{"rendered":"

\u4eca\u5e74\u306e 9\/9 \u306b\u30ea\u30ea\u30fc\u30b9\u3055\u308c\u308b\u3068\u8a00\u308f\u308c\u3066\u3044\u308b Java 8 \u3067\u6ce8\u76ee\u3057\u3066\u3044\u308b lambda \u3092\u8a66\u3057\u3066\u307f\u307e\u3057\u305f\u3002
\n
\n\u307e\u305a\u306f lambda \u304c\u4f7f\u3048\u308b JDK \u306e\u5165\u624b\u304b\u3089\u3067\u3059\u30022013-03-15 \u73fe\u5728 2\u7a2e\u985e\u306e\u30d0\u30a4\u30ca\u30ea\u304c\u3042\u308a\u307e\u3059\u306e\u3067\u6ce8\u610f\u304c\u5fc5\u8981\u3067\u3059\u3002\u5165\u624b\u5148\u306f\u3053\u3061\u3089<\/a>\u3002\u4eca\u56de\u306f b81 \u3092\u4f7f\u3063\u3066\u3044\u307e\u3059\u3002java -version<\/code> \u30b3\u30de\u30f3\u30c9\u306e\u5b9f\u884c\u7d50\u679c\u306f\u4ee5\u4e0b\u306e\u3068\u304a\u308a\u3067\u3059\u3002<\/p>\n

$ java -version\nopenjdk version \"1.8.0-ea\"\nOpenJDK Runtime Environment (build 1.8.0-ea-lambda-nightly-h3673-20130312-b81-b00)\nOpenJDK 64-Bit Server VM (build 25.0-b21, mixed mode)<\/pre>\n
lambda \u306e\u4f7f\u3044\u3069\u3053\u308d\u306f\u3044\u304f\u3064\u304b\u3042\u308b\u306e\u3067\u3059\u304c\u3001\u4e00\u756a\u306e\u4f7f\u3044\u3069\u3053\u308d\u306f\u914d\u5217\u3084\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u306e\u64cd\u4f5c\u3067\u306f\u306a\u3044\u304b\u3068\u601d\u3044\u307e\u3059\u3002\u4ee5\u524d\u306e\u30a8\u30f3\u30c8\u30ea\u3067\u3082\u7d39\u4ecb\u3057\u305f\u4ee5\u4e0b\u306e\u3088\u3046\u306a\u30b3\u30fc\u30c9\u3067\u3059\u3002<\/p>\n
[java]
\nstudents.filter((Students s) -> s.getGradYear() == 2012)
\n .map((Students s) -> s.getScore())
\n .max();
\n[\/java]<\/p>\n
\u73fe\u5728\u306f\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30af\u30e9\u30b9\u306b filter \u3084 map \u306a\u3069\u306e\u30e1\u30bd\u30c3\u30c9\u306f\u306a\u304f java.util.stream.Stream<\/code> \u30a4\u30f3\u30bf\u30d5\u30a7\u30fc\u30b9\u306b\u79fb\u3063\u3066\u3044\u307e\u3059\u3002\u305d\u306e\u305f\u3081\u914d\u5217\u3084\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30af\u30e9\u30b9\u3092 java.util.stream.Stream<\/code> \u306b\u5909\u63db\u3057\u3066\u3084\u308b\u5fc5\u8981\u304c\u3042\u308a\u307e\u3059\u3002\u914d\u5217\u306e\u5834\u5408\u306f java.util.Arrays#stream()<\/code>\u3001\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30af\u30e9\u30b9\u306e\u5834\u5408\u306f\u81ea\u8eab\u306e stream()<\/code> \u30e1\u30bd\u30c3\u30c9\u3092\u547c\u3073\u51fa\u3057\u307e\u3059\u3002API \u3092\u898b\u3066\u307f\u308b\u3068 parallelStream()<\/code> \u3068\u3044\u3046\u30e1\u30bd\u30c3\u30c9\u3082\u3042\u308a\u7c21\u5358\u306b\u4e26\u5217\u51e6\u7406\u304c\u51fa\u6765\u308b\u3088\u3046\u306b\u306a\u3063\u3066\u3044\u307e\u3059\u3002\u7c21\u5358\u306a\u691c\u8a3c\u30b3\u30fc\u30c9\u3092\u66f8\u3044\u3066\u307f\u3066\u30d9\u30f3\u30c1\u30de\u30fc\u30af\u3092\u3057\u3066\u6bd4\u8f03\u3057\u3066\u307f\u307e\u3057\u305f\u3002<\/p>\n
[java]
\nimport java.util.ArrayList;
\nimport java.util.List;
\nimport java.util.Random;
\nimport java.util.concurrent.TimeUnit;
\nimport java.util.stream.Stream;<\/p>\n
public class Bench {
\n    private List initStars(int num) {
\n        Random random = new Random();
\n        List stars = new ArrayList();<\/p>\n
        for (int i = 0; i < num; i++) {
\n            stars.add(new Star(String.valueOf(i), random.nextInt(Integer.MAX_VALUE)));
\n        }
\n        return stars;
\n    }<\/p>\n
    private int maxDistance(Stream<Star> stars) {
\n        return stars.map(p -> p.distance).reduce(0, (x, y) -> x > y ? x : y);
\n    }<\/p>\n
    private void printResult(long start, long stop, int maxDistance) {
\n        System.out.println("Max distance is " + maxDistance);
\n        System.out.println("It takes " + TimeUnit.NANOSECONDS.toMillis(stop - start) + " [ms]");
\n    }<\/p>\n
    public void start() {
\n        List<Star> stars = initStars(10_000_000);
\n        long start = System.nanoTime();
\n        int maxDistance = maxDistance(stars.stream());
\n        printResult(start, System.nanoTime(), maxDistance);<\/p>\n
        start = System.nanoTime();
\n        maxDistance = maxDistance(stars.parallelStream());
\n        printResult(start, System.nanoTime(), maxDistance);
\n    }<\/p>\n
    public static void main(String... args) {
\n        new Bench().start();
\n    }<\/p>\n
    private class Star {
\n        public final String name;
\n        public final int distance;
\n        public Star(String name, int distance) {
\n            this.name = name;
\n            this.distance = distance;
\n        }
\n    }
\n}
\n[\/java]<\/p>\n
\u5b9f\u884c\u7d50\u679c\u306f\u4ee5\u4e0b\u306e\u3068\u304a\u308a\u3067\u3059\u3002\u4f55\u5ea6\u304b\u5b9f\u884c\u3057\u3066\u307f\u307e\u3057\u305f\u304c\u4e0a\u8a18\u306e\u30b3\u30fc\u30c9\u3060\u3068\u4e26\u5217\u51e6\u7406\u306b\u3059\u308b\u3068\u534a\u5206\u7a0b\u5ea6\u306e\u51e6\u7406\u6642\u9593\u306b\u306a\u308a\u307e\u3057\u305f\u3002<\/p>\n
[bash]
\n$ javac Bench.java && java Bench
\nMax distance is 2147483222
\nIt takes 113 [ms]
\nMax distance is 2147483222
\nIt takes 57 [ms]
\n[\/bash]<\/p>\n
\u4e0a\u8a18\u306e\u30b3\u30fc\u30c9\u306e\u30e1\u30a4\u30f3\u306f\u4ee5\u4e0b\u306e\u90e8\u5206\u3067\u3059\u3002<\/p>\n
[java]
\nstars.stream().map(p -> p.distance).reduce(0, (x, y) -> x > y ? x : y);
\n[\/java]<\/p>\n
\u578b\u63a8\u8ad6\u304c\u50cd\u304f\u305f\u3081\u578b\u3092\u7701\u7565\u3057\u3066\u66f8\u3044\u3066\u3044\u307e\u3059\u304c\u3001\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u3057\u3066\u578b\u3092\u7701\u7565\u305b\u305a\u306b\u66f8\u304f\u3053\u3068\u3082\u53ef\u80fd\u3067\u3059\u3002<\/p>\n
[java]
\nstars.stream().map((Person p) -> p.distance).reduce(0, (int x, int y) -> x > y ? x : y);
\n[\/java]<\/p>\n
lambda \u5f0f\u3092\u6307\u5b9a\u3067\u304d\u308b\u3068\u3053\u308d\u306b\u306f\u30e1\u30bd\u30c3\u30c9\u3092\u6307\u5b9a\u3059\u308b\u3053\u3068\u3082\u53ef\u80fd\u3067\u3059\u3002<\/p>\n
[java]
\nstars.stream().map(p -> p.distance).reduce(0, Math::max);
\n[\/java]<\/p>\n
\u6700\u5927\u5024\u3092\u6c42\u3081\u308b\u3053\u3068\u306f\u4e00\u822c\u7684\u306a\u306e\u3067 max()<\/code> \u30e1\u30bd\u30c3\u30c9\u3082\u7528\u610f\u3055\u308c\u3066\u3044\u307e\u3059\u3002<\/p>\n
[java]
\nstars.stream().map(p -> p.distance).max().orElse(0);
\n[\/java]<\/p>\n
\u3053\u308c\u307e\u3067\u306e Java \u3068\u306f\u6bd4\u3079\u7269\u306b\u306a\u3089\u306a\u3044\u304f\u3089\u3044\u3059\u3063\u304d\u308a\u3068\u66f8\u3051\u308b\u3088\u3046\u306b\u306a\u308a\u307e\u3057\u305f\u3002\u95a2\u6570\u578b\u8a00\u8a9e\u306b\u6163\u308c\u3066\u3044\u306a\u3044\u65b9\u306b\u3068\u3063\u3066\u306f\u4e00\u898b\u826f\u304f\u308f\u304b\u3089\u306a\u3044\u304b\u3082\u3057\u308c\u307e\u305b\u3093\u304c\u3001\u6163\u308c\u308b\u3068\u8aad\u307f\u3084\u3059\u3044\u3067\u3059\u3057\u3001\u3053\u308c\u306a\u3057\u3067\u306f\u3084\u3063\u3066\u3089\u308c\u306a\u3044\u304f\u3089\u3044\u5f37\u529b\u3067\u3059\u3002Stream<\/code> \u306b\u306f filter()<\/code> \u3084 limit()<\/code> \u306a\u3069\u3088\u304f\u4f7f\u3044\u305d\u3046\u306a\u30e1\u30bd\u30c3\u30c9\u304c\u4ed6\u306b\u3082\u3042\u308a\u307e\u3059\u306e\u3067\u662f\u975e API \u3092\u78ba\u8a8d\u3057\u3066\u307f\u3066\u304f\u3060\u3055\u3044\u3002<\/p>\n
\u305d\u306e\u4ed6\u3088\u304f\u4f7f\u3044\u305d\u3046\u306a\u306e\u306f forEach()<\/code> \u30e1\u30bd\u30c3\u30c9\u3067\u3059\u306d\u3002\u3053\u3061\u3089\u306f java.lang.Iterable<\/code> \u306b\u5b9a\u7fa9\u3055\u308c\u3066\u3044\u308b\u30e1\u30bd\u30c3\u30c9\u306a\u306e\u3067\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30af\u30e9\u30b9\u304b\u3089\u305d\u306e\u307e\u307e\u3067\u547c\u3079\u307e\u3059\u3002<\/p>\n
[java]
\njava.util.Arrays.asList("foo", "bar", "baz").forEach(e -> System.out.println(e));
\n[\/java]<\/p>\n
\u3053\u3046\u306a\u3063\u3066\u304f\u308b\u3068 System.out.println<\/code> \u306e\u91cd\u539a\u3055 (?) \u304c\u30a2\u30f3\u30d0\u30e9\u30f3\u30b9\u306a\u611f\u3058\u3067\u3059\u3002\u3068\u3082\u3042\u308c Java \u3067\u3082 lambda \u304c\u4f7f\u3048\u308b\u306e\u306f\u559c\u3070\u3057\u3044\u3053\u3068\u3067\u3059\u306d\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u4eca\u5e74\u306e 9\/9 \u306b\u30ea\u30ea\u30fc\u30b9\u3055\u308c\u308b\u3068\u8a00\u308f\u308c\u3066\u3044\u308b Java 8 \u3067\u6ce8\u76ee\u3057\u3066\u3044\u308b lambda \u3092\u8a66\u3057\u3066\u307f\u307e\u3057\u305f\u3002
\n
\u7d9a\u304d\u3092\u8aad\u3080...<\/a><\/p>\n","protected":false},"author":33,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[261,262,18],"tags":[],"_links":{"self":[{"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/posts\/3397"}],"collection":[{"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/users\/33"}],"replies":[{"embeddable":true,"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/comments?post=3397"}],"version-history":[{"count":1,"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/posts\/3397\/revisions"}],"predecessor-version":[{"id":13939,"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/posts\/3397\/revisions\/13939"}],"wp:attachment":[{"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/media?parent=3397"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/categories?post=3397"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.techscore.com\/blog\/wp-json\/wp\/v2\/tags?post=3397"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}