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Java SE 9 の予習

Java

今日は私の○Ｘ回目の誕生日です。

今年は忘れられずにお祝いのプレゼントまでいただきました。(^_^)

いくつになっても誕生日を祝ってもらえるのは嬉しいものです。

と言うわけでお誕生日記念として今年の夏にリリース予定の Java SE 9 の予習をはじめます。

Java SE 9 と言えば Project Jigsaw, Project Kulla (JShell) が目玉となっています。

これらはこれから日本語での情報もたくさん出てくると思うので後回しとします。(既に最新Java情報局で記事があります。)

故に Java SE 9 を使うのであれば必要最低限これだけは覚えておきたいことを自分用メモとして載せておきます。

完全に自分用のメモです！

package jp.yucchi.jdk9eaexample;

import java.time.LocalDate;
import java.time.Period;
import java.util.List;

/**
 *
 * @author Yucchi
 */
class MyFriends {

    public enum Sex {
        MALE, FEMALE, OKAMA
    }

    int id;
    String name;
    LocalDate birthday;
    Sex gender;
    String phoneNumber;
    String profession;
    String birthplace;
    int favorabilityRating;
    List<String> hobby;

    MyFriends(int id, String name, LocalDate birthday, Sex gender, String phoneNumber, String profession, String birthplace, int favorabilityRating, List<String> hobby) {
        this.id = id;
        this.name = name;
        this.birthday = birthday;
        this.gender = gender;
        this.phoneNumber = phoneNumber;
        this.profession = profession;
        this.birthplace = birthplace;
        this.favorabilityRating = favorabilityRating;
        this.hobby = hobby;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public LocalDate getBirthday() {
        return birthday;
    }

    public Sex getGender() {
        return gender;
    }

    public String getPhoneNumber() {
        return phoneNumber;
    }

    public String getProfession() {
        return profession;
    }

    public String getBirthplace() {
        return birthplace;
    }

    public int getFavorabilityRating() {
        return favorabilityRating;
    }

    public int getAge() {
        return Period.between(birthday, LocalDate.now()).getYears();
    }

    public List<String> getHobby() {
        return hobby;
    }

    public void printMyFriends() {
        System.out.println(this.id + ": " + this.name + ", " + this.getAge() + "歳" + ", Gender: "
                + this.gender + ", 電話番号: " + this.phoneNumber
                + ", 職業: " + this.profession + ", 出身地: " + this.birthplace
                + ", 好感度: " + this.favorabilityRating + ", 趣味: " + this.hobby);
    }

}

package jp.yucchi.jdk9eaexample;

import java.time.LocalDate;

import java.time.Period;

import java.util.List;

/**

* @author Yucchi

class MyFriends {

public enum Sex {

MALE, FEMALE, OKAMA

}

int id;

String name;

LocalDate birthday;

Sex gender;

String phoneNumber;

String profession;

String birthplace;

int favorabilityRating;

List<String> hobby;

MyFriends(int id, String name, LocalDate birthday, Sex gender, String phoneNumber, String profession, String birthplace, int favorabilityRating, List<String> hobby) {

this.id = id;

this.name = name;

this.birthday = birthday;

this.gender = gender;

this.phoneNumber = phoneNumber;

this.profession = profession;

this.birthplace = birthplace;

this.favorabilityRating = favorabilityRating;

this.hobby = hobby;

}

public int getId() {

return id;

}

public String getName() {

return name;

}

public LocalDate getBirthday() {

return birthday;

}

public Sex getGender() {

return gender;

}

public String getPhoneNumber() {

return phoneNumber;

}

public String getProfession() {

return profession;

}

public String getBirthplace() {

return birthplace;

}

public int getFavorabilityRating() {

return favorabilityRating;

}

public int getAge() {

return Period.between(birthday, LocalDate.now()).getYears();

}

public List<String> getHobby() {

return hobby;

}

public void printMyFriends() {

System.out.println(this.id + ": " + this.name + ", " + this.getAge() + "歳" + ", Gender: "

+ this.gender + ", 電話番号: " + this.phoneNumber

+ ", 職業: " + this.profession + ", 出身地: " + this.birthplace

+ ", 好感度: " + this.favorabilityRating + ", 趣味: " + this.hobby);

}

package jp.yucchi.jdk9eaexample;

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

/**
 *
 * @author Yucchi
 */
public class JDK9eaExample {

    public static void main(String[] args) {

        List<MyFriends> myFriends = new ArrayList<>();

        myFriends.add(new MyFriends(1, "柴田 恭平", LocalDate.of(1951, 8, 18), MyFriends.Sex.MALE, "81300000001", "俳優", "静岡県", 80,
                List.of("野球", "サッカー", "三味線")));
        myFriends.add(new MyFriends(2, "小栗 旬", LocalDate.of(1982, 12, 26), MyFriends.Sex.MALE, "81300000002", "俳優", "東京都", 75,
                List.of("野球", "音楽鑑賞", "フィギア収集", "マンガ")));
        myFriends.add(new MyFriends(3, "市原 隼人", LocalDate.of(1987, 2, 6), MyFriends.Sex.MALE, "81300000003", "俳優", "神奈川県", 70,
                List.of("テレビゲーム", "カラオケ")));
        myFriends.add(new MyFriends(4, "安倍 晋三", LocalDate.of(1954, 9, 21), MyFriends.Sex.MALE, "81300000004", "政治家", "東京都", 40,
                List.of("ゴルフ", "映画観賞", "読書", "水泳")));
        myFriends.add(new MyFriends(5, "ドナルド トランプ", LocalDate.of(1946, 1, 20), MyFriends.Sex.MALE, "1100000005", "政治家", "ニューヨーク", 55,
                List.of("ゴルフ", "プロレス観戦")));
        myFriends.add(new MyFriends(6, "桐谷 美玲", LocalDate.of(1989, 12, 16), MyFriends.Sex.FEMALE, "81300000006", "女優", "千葉県", 95,
                List.of("音楽鑑賞", "サッカー観戦")));
        myFriends.add(new MyFriends(7, "有村 架純", LocalDate.of(1993, 2, 13), MyFriends.Sex.FEMALE, "81300000007", "女優", "兵庫県", 90,
                List.of("お菓子づくり", "散歩", "買い物")));
        myFriends.add(new MyFriends(8, "綾瀬 はるか", LocalDate.of(1985, 3, 24), MyFriends.Sex.FEMALE, "81300000008", "女優", "広島県", 85,
                List.of("カラオケ", "お菓子づくり", "足首回し")));
        myFriends.add(new MyFriends(9, "佐々木 希", LocalDate.of(1988, 2, 8), MyFriends.Sex.FEMALE, "81300000009", "女優", "秋田県", 81,
                List.of("アクセサリー収集")));
        myFriends.add(new MyFriends(10, "剛力 彩芽", LocalDate.of(1992, 8, 27), MyFriends.Sex.FEMALE, "81300000010", "女優", "神奈川県", 76,
                List.of("お菓子づくり", "フルート", "料理")));
        myFriends.add(new MyFriends(11, "堀北 真希", LocalDate.of(1988, 10, 6), MyFriends.Sex.FEMALE, "81300000011", "女優", "東京都", 88,
                List.of("読書", "サイクリング")));
        myFriends.add(new MyFriends(12, "深田 恭子", LocalDate.of(1982, 11, 2), MyFriends.Sex.FEMALE, "81300000012", "女優", "東京都", 80,
                List.of("サーフィン", "書道", "ピアノ", "水泳")));
        myFriends.add(new MyFriends(13, "小池 百合子", LocalDate.of(1952, 7, 15), MyFriends.Sex.FEMALE, "81300000013", "政治家", "兵庫県", 50,
                List.of("ゴルフ", "テニス")));
        myFriends.add(new MyFriends(14, "宇多田 ヒカル", LocalDate.of(1983, 1, 19), MyFriends.Sex.FEMALE, "81300000014", "歌手", "ニューヨーク", 91,
                List.of("読書", "マンガ", "絵画")));
        myFriends.add(new MyFriends(15, "西野 カナ", LocalDate.of(1989, 3, 18), MyFriends.Sex.FEMALE, "81300000015", "歌手", "三重県", 77,
                List.of("料理", "海外旅行")));
        myFriends.add(new MyFriends(16, "きゃりーぱみゅぱみゅ", LocalDate.of(1993, 1, 29), MyFriends.Sex.FEMALE, "81300000016", "歌手", "東京都", 74,
                List.of("釣り", "音楽")));
        myFriends.add(new MyFriends(17, "はるな 愛", LocalDate.of(1972, 7, 21), MyFriends.Sex.OKAMA, "81300000017", "おネエ系タレント", "大阪府", 69,
                List.of("釣り", "サーフィン", "スノーボード", "ゴルフ", "映画鑑賞")));
        myFriends.add(new MyFriends(18, "マツコ・デラックス", LocalDate.of(1972, 10, 26), MyFriends.Sex.OKAMA, "81300000018", "おネエ系タレント", "千葉県", 88,
                List.of("女装", "ドライブ")));

        // MyFriends 全員表示
        System.out.println("<-- MyFriends -->");
        myFriends.stream().forEach(MyFriends::printMyFriends);

        // Optional::stream
        Function<MyFriends, Optional<MyFriends>> optionalStreamMapper = mf -> mf.getFavorabilityRating() >= 80 ? Optional.of(mf) : Optional.empty();

        System.out.println("\nJava8 Optional::stream");
        myFriends.stream()
                .map(optionalStreamMapper)
                .filter(Optional::isPresent)
                .map(Optional::get)
                .collect(Collectors.toList())
                .forEach(MyFriends::printMyFriends);

        System.out.println("\nJava9 Optional::stream");
        myFriends.stream()
                .map(optionalStreamMapper)
                .flatMap(Optional::stream)
                .collect(Collectors.toList())
                .forEach(MyFriends::printMyFriends);

        // Stream ofNullable
        Function<MyFriends, MyFriends> streamOfNullableMapper = mf -> mf.getAge() < 25 ? mf : null;

        System.out.println("\nJava8 Stream ofNullable");
        myFriends.stream()
                .map(streamOfNullableMapper)
                .flatMap(s -> s != null ? Stream.of(s) : Stream.empty())
                .collect(Collectors.toList())
                .forEach(MyFriends::printMyFriends);

        System.out.println("\nJava9 Stream ofNullable");
        myFriends.stream()
                .map(streamOfNullableMapper)
                .flatMap(mf -> Stream.ofNullable(mf))
                .collect(Collectors.toList())
                .forEach(MyFriends::printMyFriends);

        System.out.println("\nID で友達を検索");
        // ID で友達を検索
        findById(7, myFriends);
        // 無効な ID で友達を検索
        findById(27, myFriends);

        System.out.println("\n名前で友達を検索");
        // 名前で友達を検索
        findByName("桐谷 美玲", myFriends);
        // 無効な名前で友達を検索
        findByName("二階堂 ふみ", myFriends);

        System.out.println("\n電話番号で友達を検索");
        // 電話番号で友達を検索
        findByPhoneNumber("1100000005", myFriends);
        // 無効な電話番号で友達を検索
        findByPhoneNumber("81300003015", myFriends);

        System.out.println("\nID、名前、電話番号の順に友達を検索");
        // ID、名前、電話番号の順に友達を検索
        // ID、名前、電話番号 すべて有効 <14: 宇多田 ヒカル, 34歳, Gender: FEMALE, 電話番号: 81300000014, 職業: 歌手, 出身地: ニューヨーク, 好感度: 911, 趣味: [読書, マンガ, 絵画]>
        findByMyFriendsIdOrNameOrPhoneNumber(14, "西野 カナ", "81300000016", myFriends);
        // 名前、電話番号 有効 <15: 西野 カナ, 27歳, Gender: FEMALE, 電話番号: 81300000015, 職業: 歌手, 出身地: 三重県, 好感度: 77, 趣味: [料理, 海外旅行]>
        findByMyFriendsIdOrNameOrPhoneNumber(99, "西野 カナ", "81300000016", myFriends);
        // 電話番号 有効 <16: きゃりーぱみゅぱみゅ, 24歳, Gender: FEMALE, 電話番号: 81300000016, 職業: 歌手, 出身地: 東京都, 好感度: 74, 趣味: [釣り, 音楽]>
        findByMyFriendsIdOrNameOrPhoneNumber(99, "二階堂 ふみ", "81300000016", myFriends);
        // ID、名前、電話番号 すべて無効
        findByMyFriendsIdOrNameOrPhoneNumber(99, "二階堂 ふみ", "81300009014", myFriends);

        System.out.println("\n職業別にグループ化し好感度 90 以上の友達を検索");
        findByProfession(myFriends, 90);

        System.out.println("\n出身地別にグループ化して友達の名前を検索");
        findByBirthplace(myFriends);

        System.out.println("\n職業別にグループ化し趣味を検索");
        findByHobbyByProfession(myFriends);

        System.out.println("\n年齢が若い順に友達を表示");
        findByYoungOrder(myFriends);

        System.out.println("\n年齢が若い順に好感度が70未満の友達がヒットするまで検索");
        findByYoungFriendsByFavorabilityRating(myFriends, 70);

        System.out.println("\n年齢が大きい順に好感度が90未満の友達がヒットするまでスキップして検索");
        findByOldFriendsByFavorabilityRating(myFriends, 90);

        System.out.println("\n条件付きで年齢が若い順に友達を表示 27歳以下スキップ、34歳まで リミット");
        findByConditionalYoungOrder(myFriends, 27, 34);

        System.out.println("\nID 1 から Double Calculation で計算して友達を検索  ただし、ID は 50 未満の範囲とする。（実質 32 まで）");
        findByIdDoubleCalculation(myFriends, 50);

    }

    // ID で友達を検索して表示する
    private static void findById(int id, List<MyFriends> myFriends) {
        Optional<MyFriends> myFriendsById = findMyFriendsById(id, myFriends);
//        // Java8  * myFriendsById.ifPresent(MyFriends::printMyFriends); だと存在しなかったときの処理ができなくて不便 (>_<)
//        if (myFriendsById.isPresent()) { // ここで既に負けている(>_<)
//            myFriendsById.get().printMyFriends();
//        } else {
//            notFoundById(id);
//        }
        myFriendsById.ifPresentOrElse(MyFriends::printMyFriends, () -> notFoundById(id));

    }

    // ID で友達を検索 Optional<MyFriends> オブジェクト取得
    private static Optional<MyFriends> findMyFriendsById(int id, List<MyFriends> myFriends) {
        return myFriends
                .stream()
                .filter(e -> e.getId() == id)
                .findFirst();
    }

    // ID で友達を検索して存在しなかった場合のメッセージを表示
    private static void notFoundById(int id) {
        System.out.println("ID " + id + " の友達は存在しません。");
    }

    // 名前で友達を検索して表示する
    private static void findByName(String name, List<MyFriends> myFriends) {
        Optional<MyFriends> myFriendsByName = findMyFriendsByName(name, myFriends);
        myFriendsByName.ifPresentOrElse(MyFriends::printMyFriends, () -> notFoundByName(name));
    }

    // 名前で友達を検索 Optional<MyFriends> オブジェクト取得
    private static Optional<MyFriends> findMyFriendsByName(String name, List<MyFriends> myFriends) {
        return myFriends
                .stream()
                .filter(e -> Objects.equals(e.getName(), name))
                .findFirst();
    }

    // 名前で友達を検索して存在しなかった場合のメッセージを表示
    private static void notFoundByName(String name) {
        System.out.println("名前 " + name + " の友達は存在しません。");
    }

    // 電話番号で友達を検索して表示する
    private static void findByPhoneNumber(String phoneNumber, List<MyFriends> myFriends) {
        Optional<MyFriends> myFriendsByPhoneNumber = findMyFriendsByPhoneNumber(phoneNumber, myFriends);
        myFriendsByPhoneNumber.ifPresentOrElse(MyFriends::printMyFriends, () -> notFoundByPhoneNumber(phoneNumber));

    }

    // 電話番号で友達を検索 Optional<MyFriends> オブジェクト取得
    private static Optional<MyFriends> findMyFriendsByPhoneNumber(String phoneNumber, List<MyFriends> myFriends) {
        return myFriends
                .stream()
                .filter(e -> Objects.equals(e.getPhoneNumber(), phoneNumber))
                .findFirst();
    }

    // 電話番号で友達を検索して存在しなかった場合のメッセージを表示
    private static void notFoundByPhoneNumber(String phoneNumber) {
        System.out.println("電話番号 " + phoneNumber + " の友達は存在しません。");
    }

    // ID、名前、電話番号の順に友達を検索して表示する
    private static void findByMyFriendsIdOrNameOrPhoneNumber(int id, String name, String phoneNumber, List<MyFriends> myFriends) {
        Optional<MyFriends> myFriendsById = findMyFriendsById(id, myFriends);
        Optional<MyFriends> myFriendsByName = findMyFriendsByName(name, myFriends);
        Optional<MyFriends> myFriendsByPhoneNumber = findMyFriendsByPhoneNumber(phoneNumber, myFriends);
        myFriendsById
                .or(() -> myFriendsByName
                .or(() -> myFriendsByPhoneNumber))
                .ifPresentOrElse(MyFriends::printMyFriends, () -> notFoundByIdOrNameOrPhoneNumber(id, name, phoneNumber));
    }

    // ID、名前、電話番号の順に友達を検索して存在しなかった場合のメッセージを表示
    private static void notFoundByIdOrNameOrPhoneNumber(int id, String name, String phoneNumber) {
        System.out.println("ID " + id + "、名前 " + name + "、電話番号 " + phoneNumber + "の何れかに合致する友達は存在しません。");
    }

    // 職業別にグループ化し好感度 90 以上の友達を検索
    private static void findByProfession(List<MyFriends> myFriends, int favorabilityRating) {
        // Java9
        Map<String, List<MyFriends>> myFriendsByProfession
                = myFriends.stream().collect(
                        Collectors.groupingBy(MyFriends::getProfession,
                                Collectors.filtering(e -> e.getFavorabilityRating() >= favorabilityRating,
                                        Collectors.toList())));

//        // Java8 No Good!!
//        Map<String, List<MyFriends>> myFriendsByProfession
//                = myFriends.stream()
//                        .filter(e -> e.getFavorabilityRating() >= favorabilityRating)
//                        .collect(
//                                Collectors.groupingBy(MyFriends::getProfession,
//                                        CollectorstoList()));
//        // Java8
//        Map<String, List<MyFriends>> myFriendsByProfession
//                = myFriends.stream().collect(
//                        Collectors.groupingBy(MyFriends::getProfession,
//                                Collectors.collectingAndThen(Collectors.toList(),
//                                        e -> e.stream()
//                                                .filter(v -> v.getFavorabilityRating() >= favorabilityRating)
//                                                .collect(Collectors.toList()))));

        myFriendsByProfession.entrySet().forEach(es -> {
            if (es.getValue().isEmpty()) {
                System.out.println("Key= " + es.getKey() + ", 好感度 " + favorabilityRating + "以上の友達は存在しません。");
            }
            es.getValue().forEach(v -> {
                System.out.println("Key= " + es.getKey() + ", Value = " + getMyFriendsInfo(v));
            });
        });
    }

    private static String getMyFriendsInfo(MyFriends v) {
        return v.getId() + ": " + v.getName() + ", " + v.getAge() + "歳" + ", Gender: "
                + v.getGender() + ", 電話番号: " + v.getPhoneNumber()
                + ", 職業: " + v.getProfession() + ", 出身地: " + v.getBirthplace()
                + ", 好感度: " + v.getFavorabilityRating() + ", 趣味: " + v.getHobby();
    }

    // 出身地別にグループ化して友達の名前を検索 Java8 で問題なしのケース
    private static void findByBirthplace(List<MyFriends> myFriends) {
        Map<String, Set<String>> myFriendsByBirthplace
                = myFriends.stream()
                        .collect(
                                Collectors.groupingBy(MyFriends::getBirthplace,
                                        Collectors.mapping(MyFriends::getName, Collectors.toSet())));

        myFriendsByBirthplace.entrySet().forEach(es -> {
            if (es.getValue().isEmpty()) {
                System.out.println("Key= " + es.getKey() + " の友達は存在しません。");
            }
            System.out.println("Key= " + es.getKey() + ", Value = " + es.getValue());
        });

    }

    // 職業別にグループ化し趣味を検索 Java9 でスマートになる
    private static void findByHobbyByProfession(List<MyFriends> myFriends) {
        Map<String, Set<String>> myFriendsByHobbyByProfession
                = myFriends.stream()
                        .collect(
                                Collectors.groupingBy(MyFriends::getProfession,
//                                        Collectors.mapping(MyFriends::getHobby, Collectors.toSet()))); // Map<String, Set<List<String>>> Java8
                                        Collectors.flatMapping(e -> e.getHobby().stream(), Collectors.toSet())));

        myFriendsByHobbyByProfession.entrySet().forEach(es -> {
            if (es.getValue().isEmpty()) {
                System.out.println("Key= " + es.getKey() + " の趣味はありません。");
            }
            System.out.println("Key= " + es.getKey() + ", Value = " + es.getValue());
        });

    }

    // 年齢が若い順に友達を表示
    private static void findByYoungOrder(List<MyFriends> myFriends) {
        myFriends.stream()
                .sorted(Comparator.comparing(MyFriends::getAge))
                .forEach(MyFriends::printMyFriends);
    }

    // 年齢が若い順に好感度が70未満の友達がヒットするまで検索
    private static void findByYoungFriendsByFavorabilityRating(List<MyFriends> myFriends, int favorabilityRating) {
        myFriends.stream()
                .sorted(Comparator.comparing(MyFriends::getAge))
                .takeWhile(e -> e.getFavorabilityRating() >= favorabilityRating)
                .forEach(MyFriends::printMyFriends);

    }

    // 年齢が大きい順に好感度が90未満の友達がヒットするまでスキップして検索
    private static void findByOldFriendsByFavorabilityRating(List<MyFriends> myFriends, int favorabilityRating) {
        myFriends.stream()
                .sorted(Comparator.comparing(MyFriends::getAge).reversed())
                .dropWhile(e -> e.getFavorabilityRating() < favorabilityRating)
                .forEach(MyFriends::printMyFriends);
    }

    // 条件付きで年齢が若い順に友達を表示 27歳以下スキップ、34歳まで リミット
    private static void findByConditionalYoungOrder(List<MyFriends> myFriends, int skip, int limit) {
        myFriends.stream()
                .sorted(Comparator.comparing(MyFriends::getAge))
                .dropWhile(e -> e.getAge() <= skip)
                .takeWhile(e -> e.getAge() <= limit)
                .forEach(MyFriends::printMyFriends);
    }

    // ID 1 から Double Calculation で計算して友達を検索  ただし、ID は 50 未満の範囲とする。（実質 32 まで）
    private static void findByIdDoubleCalculation(List<MyFriends> myFriends, int id) {
        IntStream.iterate(1, i -> i <= id, i -> i *= 2).forEach(i -> {
            findById(i, myFriends);
        });
    }

}

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package jp.yucchi.jdk9eaexample;

import java.time.LocalDate;

import java.util.ArrayList;

import java.util.Comparator;

import java.util.List;

import java.util.Map;

import java.util.Objects;

import java.util.Optional;

import java.util.Set;

import java.util.function.Function;

import java.util.stream.Collectors;

import java.util.stream.IntStream;

import java.util.stream.Stream;

/**

* @author Yucchi

public class JDK9eaExample {

public static void main(String[] args) {

List<MyFriends> myFriends = new ArrayList<>();

myFriends.add(new MyFriends(1, "柴田恭平", LocalDate.of(1951, 8, 18), MyFriends.Sex.MALE, "81300000001", "俳優", "静岡県", 80,

List.of("野球", "サッカー", "三味線")));

myFriends.add(new MyFriends(2, "小栗旬", LocalDate.of(1982, 12, 26), MyFriends.Sex.MALE, "81300000002", "俳優", "東京都", 75,

List.of("野球", "音楽鑑賞", "フィギア収集", "マンガ")));

myFriends.add(new MyFriends(3, "市原隼人", LocalDate.of(1987, 2, 6), MyFriends.Sex.MALE, "81300000003", "俳優", "神奈川県", 70,

List.of("テレビゲーム", "カラオケ")));

myFriends.add(new MyFriends(4, "安倍晋三", LocalDate.of(1954, 9, 21), MyFriends.Sex.MALE, "81300000004", "政治家", "東京都", 40,

List.of("ゴルフ", "映画観賞", "読書", "水泳")));

myFriends.add(new MyFriends(5, "ドナルドトランプ", LocalDate.of(1946, 1, 20), MyFriends.Sex.MALE, "1100000005", "政治家", "ニューヨーク", 55,

List.of("ゴルフ", "プロレス観戦")));

myFriends.add(new MyFriends(6, "桐谷美玲", LocalDate.of(1989, 12, 16), MyFriends.Sex.FEMALE, "81300000006", "女優", "千葉県", 95,

List.of("音楽鑑賞", "サッカー観戦")));

myFriends.add(new MyFriends(7, "有村架純", LocalDate.of(1993, 2, 13), MyFriends.Sex.FEMALE, "81300000007", "女優", "兵庫県", 90,

List.of("お菓子づくり", "散歩", "買い物")));

myFriends.add(new MyFriends(8, "綾瀬はるか", LocalDate.of(1985, 3, 24), MyFriends.Sex.FEMALE, "81300000008", "女優", "広島県", 85,

List.of("カラオケ", "お菓子づくり", "足首回し")));

myFriends.add(new MyFriends(9, "佐々木希", LocalDate.of(1988, 2, 8), MyFriends.Sex.FEMALE, "81300000009", "女優", "秋田県", 81,

List.of("アクセサリー収集")));

myFriends.add(new MyFriends(10, "剛力彩芽", LocalDate.of(1992, 8, 27), MyFriends.Sex.FEMALE, "81300000010", "女優", "神奈川県", 76,

List.of("お菓子づくり", "フルート", "料理")));

myFriends.add(new MyFriends(11, "堀北真希", LocalDate.of(1988, 10, 6), MyFriends.Sex.FEMALE, "81300000011", "女優", "東京都", 88,

List.of("読書", "サイクリング")));

myFriends.add(new MyFriends(12, "深田恭子", LocalDate.of(1982, 11, 2), MyFriends.Sex.FEMALE, "81300000012", "女優", "東京都", 80,

List.of("サーフィン", "書道", "ピアノ", "水泳")));

myFriends.add(new MyFriends(13, "小池百合子", LocalDate.of(1952, 7, 15), MyFriends.Sex.FEMALE, "81300000013", "政治家", "兵庫県", 50,

List.of("ゴルフ", "テニス")));

myFriends.add(new MyFriends(14, "宇多田ヒカル", LocalDate.of(1983, 1, 19), MyFriends.Sex.FEMALE, "81300000014", "歌手", "ニューヨーク", 91,

List.of("読書", "マンガ", "絵画")));

myFriends.add(new MyFriends(15, "西野カナ", LocalDate.of(1989, 3, 18), MyFriends.Sex.FEMALE, "81300000015", "歌手", "三重県", 77,

List.of("料理", "海外旅行")));

myFriends.add(new MyFriends(16, "きゃりーぱみゅぱみゅ", LocalDate.of(1993, 1, 29), MyFriends.Sex.FEMALE, "81300000016", "歌手", "東京都", 74,

List.of("釣り", "音楽")));

myFriends.add(new MyFriends(17, "はるな愛", LocalDate.of(1972, 7, 21), MyFriends.Sex.OKAMA, "81300000017", "おネエ系タレント", "大阪府", 69,

List.of("釣り", "サーフィン", "スノーボード", "ゴルフ", "映画鑑賞")));

myFriends.add(new MyFriends(18, "マツコ・デラックス", LocalDate.of(1972, 10, 26), MyFriends.Sex.OKAMA, "81300000018", "おネエ系タレント", "千葉県", 88,

List.of("女装", "ドライブ")));

// MyFriends 全員表示

System.out.println("<-- MyFriends -->");

myFriends.stream().forEach(MyFriends::printMyFriends);

// Optional::stream

Function<MyFriends, Optional<MyFriends>> optionalStreamMapper = mf -> mf.getFavorabilityRating() >= 80 ? Optional.of(mf) : Optional.empty();

System.out.println("\nJava8 Optional::stream");

myFriends.stream()

.map(optionalStreamMapper)

.filter(Optional::isPresent)

.map(Optional::get)

.collect(Collectors.toList())

.forEach(MyFriends::printMyFriends);

System.out.println("\nJava9 Optional::stream");

myFriends.stream()

.map(optionalStreamMapper)

.flatMap(Optional::stream)

.collect(Collectors.toList())

.forEach(MyFriends::printMyFriends);

// Stream ofNullable

Function<MyFriends, MyFriends> streamOfNullableMapper = mf -> mf.getAge() < 25 ? mf : null;

System.out.println("\nJava8 Stream ofNullable");

myFriends.stream()

.map(streamOfNullableMapper)

.flatMap(s -> s != null ? Stream.of(s) : Stream.empty())

.collect(Collectors.toList())

.forEach(MyFriends::printMyFriends);

System.out.println("\nJava9 Stream ofNullable");

myFriends.stream()

.map(streamOfNullableMapper)

.flatMap(mf -> Stream.ofNullable(mf))

.collect(Collectors.toList())

.forEach(MyFriends::printMyFriends);

System.out.println("\nID で友達を検索");

// ID で友達を検索

findById(7, myFriends);

// 無効な ID で友達を検索

findById(27, myFriends);

System.out.println("\n名前で友達を検索");

// 名前で友達を検索

findByName("桐谷美玲", myFriends);

// 無効な名前で友達を検索

findByName("二階堂ふみ", myFriends);

System.out.println("\n電話番号で友達を検索");

// 電話番号で友達を検索

findByPhoneNumber("1100000005", myFriends);

// 無効な電話番号で友達を検索

findByPhoneNumber("81300003015", myFriends);

System.out.println("\nID、名前、電話番号の順に友達を検索");

// ID、名前、電話番号の順に友達を検索

// ID、名前、電話番号すべて有効 <14: 宇多田ヒカル, 34歳, Gender: FEMALE, 電話番号: 81300000014, 職業: 歌手, 出身地: ニューヨーク, 好感度: 911, 趣味: [読書, マンガ, 絵画]>

findByMyFriendsIdOrNameOrPhoneNumber(14, "西野カナ", "81300000016", myFriends);

// 名前、電話番号有効 <15: 西野カナ, 27歳, Gender: FEMALE, 電話番号: 81300000015, 職業: 歌手, 出身地: 三重県, 好感度: 77, 趣味: [料理, 海外旅行]>

findByMyFriendsIdOrNameOrPhoneNumber(99, "西野カナ", "81300000016", myFriends);

// 電話番号有効 <16: きゃりーぱみゅぱみゅ, 24歳, Gender: FEMALE, 電話番号: 81300000016, 職業: 歌手, 出身地: 東京都, 好感度: 74, 趣味: [釣り, 音楽]>

findByMyFriendsIdOrNameOrPhoneNumber(99, "二階堂ふみ", "81300000016", myFriends);

// ID、名前、電話番号すべて無効

findByMyFriendsIdOrNameOrPhoneNumber(99, "二階堂ふみ", "81300009014", myFriends);

System.out.println("\n職業別にグループ化し好感度 90 以上の友達を検索");

findByProfession(myFriends, 90);

System.out.println("\n出身地別にグループ化して友達の名前を検索");

findByBirthplace(myFriends);

System.out.println("\n職業別にグループ化し趣味を検索");

findByHobbyByProfession(myFriends);

System.out.println("\n年齢が若い順に友達を表示");

findByYoungOrder(myFriends);

System.out.println("\n年齢が若い順に好感度が70未満の友達がヒットするまで検索");

findByYoungFriendsByFavorabilityRating(myFriends, 70);

System.out.println("\n年齢が大きい順に好感度が90未満の友達がヒットするまでスキップして検索");

findByOldFriendsByFavorabilityRating(myFriends, 90);

System.out.println("\n条件付きで年齢が若い順に友達を表示 27歳以下スキップ、34歳までリミット");

findByConditionalYoungOrder(myFriends, 27, 34);

System.out.println("\nID 1 から Double Calculation で計算して友達を検索ただし、ID は 50 未満の範囲とする。（実質 32 まで）");

findByIdDoubleCalculation(myFriends, 50);

}

// ID で友達を検索して表示する

private static void findById(int id, List<MyFriends> myFriends) {

Optional<MyFriends> myFriendsById = findMyFriendsById(id, myFriends);

// // Java8 * myFriendsById.ifPresent(MyFriends::printMyFriends); だと存在しなかったときの処理ができなくて不便 (>_<)

// if (myFriendsById.isPresent()) { // ここで既に負けている(>_<)

// myFriendsById.get().printMyFriends();

// } else {

// notFoundById(id);

// }

myFriendsById.ifPresentOrElse(MyFriends::printMyFriends, () -> notFoundById(id));

}

// ID で友達を検索 Optional<MyFriends> オブジェクト取得

private static Optional<MyFriends> findMyFriendsById(int id, List<MyFriends> myFriends) {

return myFriends

.stream()

.filter(e -> e.getId() == id)

.findFirst();

}

// ID で友達を検索して存在しなかった場合のメッセージを表示

private static void notFoundById(int id) {

System.out.println("ID " + id + " の友達は存在しません。");

}

// 名前で友達を検索して表示する

private static void findByName(String name, List<MyFriends> myFriends) {

Optional<MyFriends> myFriendsByName = findMyFriendsByName(name, myFriends);

myFriendsByName.ifPresentOrElse(MyFriends::printMyFriends, () -> notFoundByName(name));

}

// 名前で友達を検索 Optional<MyFriends> オブジェクト取得

private static Optional<MyFriends> findMyFriendsByName(String name, List<MyFriends> myFriends) {

return myFriends

.stream()

.filter(e -> Objects.equals(e.getName(), name))

.findFirst();

}

// 名前で友達を検索して存在しなかった場合のメッセージを表示

private static void notFoundByName(String name) {

System.out.println("名前 " + name + " の友達は存在しません。");

}

// 電話番号で友達を検索して表示する

private static void findByPhoneNumber(String phoneNumber, List<MyFriends> myFriends) {

Optional<MyFriends> myFriendsByPhoneNumber = findMyFriendsByPhoneNumber(phoneNumber, myFriends);

myFriendsByPhoneNumber.ifPresentOrElse(MyFriends::printMyFriends, () -> notFoundByPhoneNumber(phoneNumber));

}

// 電話番号で友達を検索 Optional<MyFriends> オブジェクト取得

private static Optional<MyFriends> findMyFriendsByPhoneNumber(String phoneNumber, List<MyFriends> myFriends) {

return myFriends

.stream()

.filter(e -> Objects.equals(e.getPhoneNumber(), phoneNumber))

.findFirst();

}

// 電話番号で友達を検索して存在しなかった場合のメッセージを表示

private static void notFoundByPhoneNumber(String phoneNumber) {

System.out.println("電話番号 " + phoneNumber + " の友達は存在しません。");

}

// ID、名前、電話番号の順に友達を検索して表示する

private static void findByMyFriendsIdOrNameOrPhoneNumber(int id, String name, String phoneNumber, List<MyFriends> myFriends) {

Optional<MyFriends> myFriendsById = findMyFriendsById(id, myFriends);

Optional<MyFriends> myFriendsByName = findMyFriendsByName(name, myFriends);

Optional<MyFriends> myFriendsByPhoneNumber = findMyFriendsByPhoneNumber(phoneNumber, myFriends);

myFriendsById

.or(() -> myFriendsByName

.or(() -> myFriendsByPhoneNumber))

.ifPresentOrElse(MyFriends::printMyFriends, () -> notFoundByIdOrNameOrPhoneNumber(id, name, phoneNumber));

}

// ID、名前、電話番号の順に友達を検索して存在しなかった場合のメッセージを表示

private static void notFoundByIdOrNameOrPhoneNumber(int id, String name, String phoneNumber) {

System.out.println("ID " + id + "、名前 " + name + "、電話番号 " + phoneNumber + "の何れかに合致する友達は存在しません。");

}

// 職業別にグループ化し好感度 90 以上の友達を検索

private static void findByProfession(List<MyFriends> myFriends, int favorabilityRating) {

// Java9

Map<String, List<MyFriends>> myFriendsByProfession

= myFriends.stream().collect(

Collectors.groupingBy(MyFriends::getProfession,

Collectors.filtering(e -> e.getFavorabilityRating() >= favorabilityRating,

Collectors.toList())));

// // Java8 No Good!!

// Map<String, List<MyFriends>> myFriendsByProfession

// = myFriends.stream()

// .filter(e -> e.getFavorabilityRating() >= favorabilityRating)

// .collect(

// Collectors.groupingBy(MyFriends::getProfession,

// CollectorstoList()));

// // Java8

// Map<String, List<MyFriends>> myFriendsByProfession

// = myFriends.stream().collect(

// Collectors.groupingBy(MyFriends::getProfession,

// Collectors.collectingAndThen(Collectors.toList(),

// e -> e.stream()

// .filter(v -> v.getFavorabilityRating() >= favorabilityRating)

// .collect(Collectors.toList()))));

myFriendsByProfession.entrySet().forEach(es -> {

if (es.getValue().isEmpty()) {

System.out.println("Key= " + es.getKey() + ", 好感度 " + favorabilityRating + "以上の友達は存在しません。");

}

es.getValue().forEach(v -> {

System.out.println("Key= " + es.getKey() + ", Value = " + getMyFriendsInfo(v));

});

}

private static String getMyFriendsInfo(MyFriends v) {

return v.getId() + ": " + v.getName() + ", " + v.getAge() + "歳" + ", Gender: "

+ v.getGender() + ", 電話番号: " + v.getPhoneNumber()

+ ", 職業: " + v.getProfession() + ", 出身地: " + v.getBirthplace()

+ ", 好感度: " + v.getFavorabilityRating() + ", 趣味: " + v.getHobby();

}

// 出身地別にグループ化して友達の名前を検索 Java8 で問題なしのケース

private static void findByBirthplace(List<MyFriends> myFriends) {

Map<String, Set<String>> myFriendsByBirthplace

= myFriends.stream()

.collect(

Collectors.groupingBy(MyFriends::getBirthplace,

Collectors.mapping(MyFriends::getName, Collectors.toSet())));

myFriendsByBirthplace.entrySet().forEach(es -> {

if (es.getValue().isEmpty()) {

System.out.println("Key= " + es.getKey() + " の友達は存在しません。");

}

System.out.println("Key= " + es.getKey() + ", Value = " + es.getValue());

});

}

// 職業別にグループ化し趣味を検索 Java9 でスマートになる

private static void findByHobbyByProfession(List<MyFriends> myFriends) {

Map<String, Set<String>> myFriendsByHobbyByProfession

= myFriends.stream()

.collect(

Collectors.groupingBy(MyFriends::getProfession,

// Collectors.mapping(MyFriends::getHobby, Collectors.toSet()))); // Map<String, Set<List<String>>> Java8

Collectors.flatMapping(e -> e.getHobby().stream(), Collectors.toSet())));

myFriendsByHobbyByProfession.entrySet().forEach(es -> {

if (es.getValue().isEmpty()) {

System.out.println("Key= " + es.getKey() + " の趣味はありません。");

}

System.out.println("Key= " + es.getKey() + ", Value = " + es.getValue());

});

}

// 年齢が若い順に友達を表示

private static void findByYoungOrder(List<MyFriends> myFriends) {

myFriends.stream()

.sorted(Comparator.comparing(MyFriends::getAge))

.forEach(MyFriends::printMyFriends);

}

// 年齢が若い順に好感度が70未満の友達がヒットするまで検索

private static void findByYoungFriendsByFavorabilityRating(List<MyFriends> myFriends, int favorabilityRating) {

myFriends.stream()

.sorted(Comparator.comparing(MyFriends::getAge))

.takeWhile(e -> e.getFavorabilityRating() >= favorabilityRating)

.forEach(MyFriends::printMyFriends);

}

// 年齢が大きい順に好感度が90未満の友達がヒットするまでスキップして検索

private static void findByOldFriendsByFavorabilityRating(List<MyFriends> myFriends, int favorabilityRating) {

myFriends.stream()

.sorted(Comparator.comparing(MyFriends::getAge).reversed())

.dropWhile(e -> e.getFavorabilityRating() < favorabilityRating)

.forEach(MyFriends::printMyFriends);

}

// 条件付きで年齢が若い順に友達を表示 27歳以下スキップ、34歳までリミット

private static void findByConditionalYoungOrder(List<MyFriends> myFriends, int skip, int limit) {

myFriends.stream()

.sorted(Comparator.comparing(MyFriends::getAge))

.dropWhile(e -> e.getAge() <= skip)

.takeWhile(e -> e.getAge() <= limit)

.forEach(MyFriends::printMyFriends);

}

// ID 1 から Double Calculation で計算して友達を検索ただし、ID は 50 未満の範囲とする。（実質 32 まで）

private static void findByIdDoubleCalculation(List<MyFriends> myFriends, int id) {

IntStream.iterate(1, i -> i <= id, i -> i *= 2).forEach(i -> {

findById(i, myFriends);

});

}

static <E> List<E> of()

Returns an immutable list containing zero elements. See Immutable List Static Factory Methods for details.

Type Parameters:
E – the List’s element type

Returns:
an empty List

public Stream<T> stream()

If a value is present, returns a sequential Stream containing only that value, otherwise returns an empty Stream.

API Note:
This method can be used to transform a Stream of optional elements to a Stream of present value elements:

Stream<Optional<T>> os = ..
Stream<T> s = os.flatMap(Optional::stream)

Returns:
the optional value as a Stream

static <T> Stream<T> ofNullable(T t)

Returns a sequential Stream containing a single element, if non-null, otherwise returns an empty Stream.

Type Parameters:
T – the type of stream elements

Parameters:
t – the single element

Returns:
a stream with a single element if the specified element is non-null, otherwise an empty stream

public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction)

If a value is present, performs the given action with the value, otherwise performs the given empty-based action.

Parameters:
action – the action to be performed, if a value is presentemptyAction – the empty-based action to be performed, if no value is present

Throws:
NullPointerException – if a value is present and the given action is null, or no value is present and the given empty-based action is null.

public Optional<T> or(Supplier<? extends Optional<? extends T>> supplier)

If a value is present, returns an Optional describing the value, otherwise returns an Optional produced by the supplying function.

Parameters:
supplier – the supplying function that produces an Optional to be returned

Returns:
returns an Optional describing the value of this Optional, if a value is present, otherwise an Optional produced by the supplying function.

Throws:
NullPointerException – if the supplying function is null or produces a null result

public static <T,A,R> Collector<T,?,R> filtering(Predicate<? super T> predicate, Collector<? super T,A,R> downstream)

Adapts a Collector to one accepting elements of the same type T by applying the predicate to each input element and only accumulating if the predicate returns true.

API Note:
The filtering() collectors are most useful when used in a multi-level reduction, such as downstream of a groupingBy or partitioningBy. For example, given a stream of Employee, to accumulate the employees in each department that have a salary above a certain threshold:

Map<Department, Set<Employee>> wellPaidEmployeesByDepartment
   = employees.stream().collect(
     groupingBy(Employee::getDepartment,
                filtering(e -> e.getSalary() > 2000,
                          toSet())));

A filtering collector differs from a stream’s filter() operation. In this example, suppose there are no employees whose salary is above the threshold in some department. Using a filtering collector as shown above would result in a mapping from that department to an empty Set. If a stream filter() operation were done instead, there would be no mapping for that department at all.

Type Parameters:
T – the type of the input elements
A – intermediate accumulation type of the downstream collector
R – result type of collector

Parameters:
predicate – a predicate to be applied to the input elements
downstream – a collector which will accept values that match the predicate

Returns:
a collector which applies the predicate to the input elements and provides matching elements to the downstream collector

public static <T,U,A,R> Collector<T,?,R> flatMapping(Function<? super T,? extends Stream<? extends U>> mapper, Collector<? super U,A,R> downstream)

Adapts a Collector accepting elements of type U to one accepting elements of type T by applying a flat mapping function to each input element before accumulation. The flat mapping function maps an input element to a stream covering zero or more output elements that are then accumulated downstream. Each mapped stream is closed after its contents have been placed downstream. (If a mapped stream is null an empty stream is used, instead.)

API Note:
The flatMapping() collectors are most useful when used in a multi-level reduction, such as downstream of a groupingBy or partitioningBy. For example, given a stream of Order, to accumulate the set of line items for each customer:

Map<String, Set<LineItem>> itemsByCustomerName
   = orders.stream().collect(
     groupingBy(Order::getCustomerName,
                flatMapping(order -> order.getLineItems().stream(),
                            toSet())));

Type Parameters:
T – the type of the input elements
U – type of elements accepted by downstream collector
A – intermediate accumulation type of the downstream collector
R – result type of collector

Parameters:
mapper – a function to be applied to the input elements, which returns a stream of results
downstream – a collector which will receive the elements of the stream returned by mapper

Returns:
a collector which applies the mapping function to the input elements and provides the flat mapped results to the downstream collector

default Stream<T> takeWhile(Predicate<? super T> predicate)

Returns, if this stream is ordered, a stream consisting of the longest prefix of elements taken from this stream that match the given predicate. Otherwise returns, if this stream is unordered, a stream consisting of a subset of elements taken from this stream that match the given predicate.

If this stream is ordered then the longest prefix is a contiguous sequence of elements of this stream that match the given predicate. The first element of the sequence is the first element of this stream, and the element immediately following the last element of the sequence does not match the given predicate.

If this stream is unordered, and some (but not all) elements of this stream match the given predicate, then the behavior of this operation is nondeterministic; it is free to take any subset of matching elements (which includes the empty set).

Independent of whether this stream is ordered or unordered if all elements of this stream match the given predicate then this operation takes all elements (the result is the same as the input), or if no elements of the stream match the given predicate then no elements are taken (the result is an empty stream).

This is a short-circuiting stateful intermediate operation.

API Note:
While takeWhile() is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, since the operation is constrained to return not just any valid prefix, but the longest prefix of elements in the encounter order. Using an unordered stream source (such as generate(Supplier)) or removing the ordering constraint with BaseStream.unordered() may result in significant speedups of takeWhile() in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization with takeWhile() in parallel pipelines, switching to sequential execution with BaseStream.sequential() may improve performance.

Implementation Requirements:
The default implementation obtains the spliterator of this stream, wraps that spliterator so as to support the semantics of this operation on traversal, and returns a new stream associated with the wrapped spliterator. The returned stream preserves the execution characteristics of this stream (namely parallel or sequential execution as per BaseStream.isParallel()) but the wrapped spliterator may choose to not support splitting. When the returned stream is closed, the close handlers for both the returned and this stream are invoked.

Parameters:
predicate – a non-interfering, stateless predicate to apply to elements to determine the longest prefix of elements.

Returns:
the new stream

default Stream<T> dropWhile(Predicate<? super T> predicate)

Returns, if this stream is ordered, a stream consisting of the remaining elements of this stream after dropping the longest prefix of elements that match the given predicate. Otherwise returns, if this stream is unordered, a stream consisting of the remaining elements of this stream after dropping a subset of elements that match the given predicate.

If this stream is ordered then the longest prefix is a contiguous sequence of elements of this stream that match the given predicate. The first element of the sequence is the first element of this stream, and the element immediately following the last element of the sequence does not match the given predicate.

If this stream is unordered, and some (but not all) elements of this stream match the given predicate, then the behavior of this operation is nondeterministic; it is free to drop any subset of matching elements (which includes the empty set).

Independent of whether this stream is ordered or unordered if all elements of this stream match the given predicate then this operation drops all elements (the result is an empty stream), or if no elements of the stream match the given predicate then no elements are dropped (the result is the same as the input).

This is a stateful intermediate operation.

API Note:
While dropWhile() is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, since the operation is constrained to return not just any valid prefix, but the longest prefix of elements in the encounter order. Using an unordered stream source (such as generate(Supplier)) or removing the ordering constraint with BaseStream.unordered() may result in significant speedups of dropWhile() in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization with dropWhile() in parallel pipelines, switching to sequential execution with BaseStream.sequential() may improve performance.

Implementation Requirements:
The default implementation obtains the spliterator of this stream, wraps that spliterator so as to support the semantics of this operation on traversal, and returns a new stream associated with the wrapped spliterator. The returned stream preserves the execution characteristics of this stream (namely parallel or sequential execution as per BaseStream.isParallel()) but the wrapped spliterator may choose to not support splitting. When the returned stream is closed, the close handlers for both the returned and this stream are invoked.

Parameters:
predicate – a non-interfering, stateless predicate to apply to elements to determine the longest prefix of elements.

Returns:
the new stream

static IntStream iterate(int seed, IntPredicate hasNext, IntUnaryOperator next)

Returns a sequential ordered IntStream produced by iterative application of the given next function to an initial element, conditioned on satisfying the given hasNext predicate. The stream terminates as soon as the hasNext predicate returns false.

IntStream.iterate should produce the same sequence of elements as produced by the corresponding for-loop:

     for (int index=seed; hasNext.test(index); index = next.applyAsInt(index)) {
         …
     }

The resulting sequence may be empty if the hasNext predicate does not hold on the seed value. Otherwise the first element will be the supplied seed value, the next element (if present) will be the result of applying the next function to the seed value, and so on iteratively until the hasNext predicate indicates that the stream should terminate.

The action of applying the hasNext predicate to an element happens-before the action of applying the next function to that element. The action of applying the next function for one element happens-before the action of applying the hasNext predicate for subsequent elements. For any given element an action may be performed in whatever thread the library chooses.

Parameters:
seed – the initial element
hasNext – a predicate to apply to elements to determine when the stream must terminate.
next – a function to be applied to the previous element to produce a new element

Returns:
a new sequential IntStream

static <T> Stream<T> iterate(T seed, Predicate<? super T> hasNext, UnaryOperator<T> next)

Returns a sequential ordered Stream produced by iterative application of the given next function to an initial element, conditioned on satisfying the given hasNext predicate. The stream terminates as soon as the hasNext predicate returns false.

Stream.iterate should produce the same sequence of elements as produced by the corresponding for-loop:

     for (T index=seed; hasNext.test(index); index = next.apply(index)) {
         …
     }

Type Parameters:
T – the type of stream elements

Returns:
a new sequential Stream

API ドキュメントが英語しかないのが残念(>_<)

正式リリースされる頃には日本語版が出ることを祈ろう！

Java SE 8 からの痒いところに手が届いたようなアップデートだけどかなり便利になる。

なぜ初めからこうしなかったんだろうと思うほどに。

でも zip, pair はまだ無いまま・・・

Java SE 10 まで待つことになるのか必要ないと判断されたのか？

他にもいろいろ細かいところが良くなっているようだから正式リリースが楽しみですね！

Hatena タグ: Java

TAGS: Java | 2017年2月18日9:48 PM

« A-2 フライトジャケット　買っちまったぜ！ Java SE 9 の予習その２ »

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