Java8涓殑Stream

Posted 2020-11-25

鏍囩锛?a href='http://www.mamicode.com/so/1/getc' title='getc'>getc   鍏冪礌   static   tag   override   鎺掑簭   student   com   甯哥敤   

java8涔熷嚭鏉ュソ涔呬簡锛屾帴鍙ｉ粯璁ゆ柟娉曪紝lambda琛ㄨ揪寮忥紝鍑芥暟寮忔帴鍙ｏ紝Date API绛夌壒鎬ц繕鏄湁蹇呰鍘讳簡瑙ｄ竴涓嬨€傛瘮濡傚湪椤圭洰涓粡甯哥敤鍒伴泦鍚堬紝閬嶅巻闆嗗悎鍙互璇曚笅lambda琛ㄨ揪寮忥紝缁忓父杩樿瀵归泦鍚堣繘琛岃繃婊ゅ拰鎺掑簭锛孲tream灏辨淳涓婄敤鍦轰簡銆?/p>

Stream浣滀负java8鐨勬柊鐗规€э紝鍩轰簬lambda琛ㄨ揪寮忥紝鏄闆嗗悎瀵硅薄鍔熻兘鐨勫寮猴紝瀹冧笓娉ㄤ簬瀵归泦鍚堝璞¤繘琛屽悇绉嶆悶绗戯紝渚垮埄鐨勮仛鍚堟搷浣滄垨鑰呭ぇ鎵归噺鐨勬暟鎹搷浣滐紝鎻愰珮浜嗙紪绋嬫晥鐜囧拰浠ｇ爜鍙鎬с€?/p>

Stream鐨勫師鐞嗭細灏嗚澶勭悊鐨勫厓绱犵湅浣滀竴绉嶆祦锛岀暀鍦ㄧ閬撲腑浼犺緭锛屽苟涓斿彲浠ュ湪绠￠亾鐨勮妭鐐逛笂澶勭悊锛屽寘鎷繃婊ょ瓫閫夈€佸幓閲嶃€佹帓搴忋€佽仛鍚堢瓑銆傚厓绱犳祦鍦ㄧ閬撲腑缁忚繃涓棿鎿嶄綔鐨勫鐞嗭紝鏈€鍚庣敱鏈€缁堟搷浣滃緱鍒板墠闈㈠鐞嗙殑缁撴灉銆?/p>

闆嗗悎鏈変袱绉嶆柟寮忕敓鎴愭祦锛?/p>

• stream() - 涓洪泦鍚堝垱寤轰覆琛屾祦
• parallelStream() - 涓洪泦鍚堝垱寤哄苟琛屾祦
  

涓婂浘涓槸Stream绫荤殑绫荤粨鏋勫浘锛岄噷闈㈠寘鍚簡澶ч儴鍒嗙殑涓棿鍜岀粓姝㈡搷浣溿€?/p>

涓棿鎿嶄綔涓昏鏈変互涓嬫柟娉曪紙姝ょ被鍨嬫柟娉曡繑鍥炵殑閮芥槸Stream锛夛細map (mapToInt, flatMap 绛?銆?filter銆?distinct銆?sorted銆?peek銆?limit銆?skip銆?parallel銆?sequential銆?unordered

缁堟鎿嶄綔涓昏鏈変互涓嬫柟娉曪細forEach銆?forEachOrdered銆?toArray銆?reduce銆?collect銆?min銆?max銆?count銆?anyMatch銆?allMatch銆?noneMatch銆?findFirst銆?findAny銆?iterator

涓句緥璇存槑

棣栧厛涓轰簡璇存槑Stream瀵瑰璞￠泦鍚堢殑鎿嶄綔锛屾柊寤轰竴涓猄tudent绫伙紙瀛︾敓绫伙級,瑕嗗啓浜唀quals()鍜宧ashCode()鏂规硶

public class Student {
    private Long id;
    private String name;
    private int age;
    private String address;

    public Student() {
    }

    public Student(Long id, String name, int age, String address) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.address = address;
    }

    @Override
    public boolean equals(Object object) {
        if (this == object) return true;
        if (object == null || getClass() != object.getClass()) return false;
        Student student = (Student) object;
        return age == student.age &&
                Objects.equals(id, student.id) &&
                Objects.equals(name, student.name) &&
                Objects.equals(address, student.address);
    }

    @Override
    public int hashCode() {

        return Objects.hash(id, name, age, address);
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

public static void main(String[] args) { Student s1 = new Student(1L, "鑲栨垬", 15, "娴欐睙"); Student s2 = new Student(2L, "鐜嬩竴鍗?quot;, 15, "婀栧寳"); Student s3 = new Student(3L, "鏉ㄧ传", 17, "鍖椾含"); Student s4 = new Student(4L, "鏉庣幇", 17, "娴欐睙"); List<Student> students = new ArrayList<>(); students.add(s1); students.add(s2); students.add(s3); students.add(s4); List<Student> streamStudents = testFilter(students); streamStudents.forEach(System.out::println); } /** * 闆嗗悎绛涢€? * @param students * @return */ private static List<Student> testFilter(List<Student> students) { return students.stream().filter(s -> "娴欐睙".equals(s.getAddress())).collect(Collectors.toList()); }

map(杞崲)

public static void main(String[] args) {
        Student s1 = new Student(1L, "鑲栨垬", 15, "娴欐睙");
        Student s2 = new Student(2L, "鐜嬩竴鍗?quot;, 15, "婀栧寳");
        Student s3 = new Student(3L, "鏉ㄧ传", 17, "鍖椾含");
        Student s4 = new Student(4L, "鏉庣幇", 17, "娴欐睙");
        List<Student> students = new ArrayList<>();
        students.add(s1);
        students.add(s2);
        students.add(s3);
        students.add(s4);

        List<Student> streamStudents = testFilter(students);
        testMap(students);
    }

    /**
     * 闆嗗悎杞崲
     * @param students
     */
    private static void testMap(List<Student> students) {
        // 鍦ㄥ湴鍧€鍓嶉潰鍔犱笂閮ㄥ垎淇℃伅锛屽彧鑾峰彇鍦板潃杈撳嚭
        List<String> address = students.stream().map(s -> "浣忓潃:" + s.getAddress()).collect(Collectors.toList());
        address.forEach(a -> System.out.println(a));
    }

distinct(鍘婚噸)

public static void main(String[] args) {
        testDistinct1();
    }

    /**
     * 闆嗗悎鍘婚噸锛堝熀鏈被鍨嬶級
     */
    private static void testDistinct1() {
        // 绠€鍗曞瓧绗︿覆鐨勫幓閲?        List<String> list = Arrays.asList("111", "222", "333", "111", "222");
        list.stream().distinct().forEach(System.out::println);
    }

public static void main(String [] args) {
      testDistinct2();
    }

    /**
     * 闆嗗悎鍘婚噸锛堝紩鐢ㄥ璞★級
     */
    private static void testDistinct2() {
        //寮曠敤瀵硅薄鐨勫幓閲嶏紝寮曠敤瀵硅薄瑕佸疄鐜癶ashCode鍜宔qual鏂规硶锛屽惁鍒欏幓閲嶆棤鏁?        Student s1 = new Student(1L, "鑲栨垬", 15, "娴欐睙");
        Student s2 = new Student(2L, "鐜嬩竴鍗?quot;, 15, "婀栧寳");
        Student s3 = new Student(3L, "鏉ㄧ传", 17, "鍖椾含");
        Student s4 = new Student(4L, "鏉庣幇", 17, "娴欐睙");
        Student s5 = new Student(1L, "鑲栨垬", 15, "娴欐睙");
        List<Student> students = new ArrayList<>();
        students.add(s1);
        students.add(s2);
        students.add(s3);
        students.add(s4);
        students.add(s5);
        students.stream().distinct().forEach(System.out::println);
    }

杩愯缁撴灉锛?/p>

Student{id=1, name='鑲栨垬', age=15, address='娴欐睙'}
Student{id=2, name='鐜嬩竴鍗?#39;, age=15, address='婀栧寳'}
Student{id=3, name='鏉ㄧ传', age=17, address='鍖椾含'}
Student{id=4, name='鏉庣幇', age=17, address='娴欐睙'}

鍙互鐪嬪嚭锛屼袱涓噸澶嶇殑鈥滆倴鎴樷€濆悓瀛﹁繘琛屼簡鍘婚噸锛岃繖涓嶄粎鍥犱负浣跨敤浜哾istinct()鏂规硶锛岃€屼笖鍥犱负Student瀵硅薄閲嶅啓浜唀quals鍜宧ashCode()鏂规硶锛屽惁鍒欏幓閲嶆槸鏃犳晥鐨?/p>

sorted(鎺掑簭)

public static void main(String[] args) {
        testSort();
    }

    /**
     * 闆嗗悎鎺掑簭锛堟寚瀹氭帓搴忚鍒欙級
     */
    private static void testSort() {
        Student s1 = new Student(1L, "鑲栨垬", 15, "娴欐睙");
        Student s2 = new Student(2L, "鐜嬩竴鍗?quot;, 15, "婀栧寳");
        Student s3 = new Student(3L, "鏉ㄧ传", 17, "鍖椾含");
        Student s4 = new Student(4L, "鏉庣幇", 17, "娴欐睙");
        List<Student> students = new ArrayList<>();
        students.add(s1);
        students.add(s2);
        students.add(s3);
        students.add(s4);
        students.stream()
                .sorted((stu1, stu2) -> Long.compare(stu2.getId(), stu1.getId()))
                .sorted((stu1, stu2) -> Integer.compare(stu2.getAge(), stu1.getAge()))
                .forEach(System.out::println);
    }

limit(闄愬埗杩斿洖涓暟)

public static void main(String[] args) {
        testLimit();
    }

    /**
     * 闆嗗悎limit锛岃繑鍥炲墠鍑犱釜鍏冪礌
     */
    private static void testLimit() {
        List<String> list = Arrays.asList("333", "222", "111");
        list.stream().limit(2).forEach(System.out::println);
    }

skip(鍒犻櫎鍏冪礌)

public static void main(String[] args) {
        testSkip();
    }

    /**
     * 闆嗗悎skip锛屽垹闄ゅ墠n涓厓绱?     */
    private static void testSkip() {
        List<String> list = Arrays.asList("333", "222", "111");
        list.stream().skip(2).forEach(System.out::println);
    }

reduce锛堣仛鍚堬級

public static void main(String[] args) {
    testReduce();
}

/**
 * 闆嗗悎reduce锛屽皢闆嗗悎涓瘡涓厓绱犳暣鍚堟垚涓€鏉℃暟鎹? */
private static void testReduce() {
    List<String> list = Arrays.asList("娆?quot;, "杩?quot;, "浣?quot;);
    String appendStr = list.stream().reduce("鍖椾含", (a, b) -> a + b);
    System.out.println(appendStr);
}

anyMatch/allMatch/noneMatch锛堝尮閰?/h3>

public static void main(String[] args) {
        testMatch();
    }

    /**
     * anyMatch锛歋tream 涓换鎰忎竴涓厓绱犵鍚堜紶鍏ョ殑 predicate锛岃繑鍥?true
       allMatch锛歋tream 涓叏閮ㄥ厓绱犵鍚堜紶鍏ョ殑 predicate锛岃繑鍥?true
       noneMatch锛歋tream 涓病鏈変竴涓厓绱犵鍚堜紶鍏ョ殑 predicate锛岃繑鍥?true
     */
    private static void testMatch() {
        Student s1 = new Student(1L, "鑲栨垬", 15, "娴欐睙");
        Student s2 = new Student(2L, "鐜嬩竴鍗?quot;, 15, "婀栧寳");
        Student s3 = new Student(3L, "鏉ㄧ传", 17, "鍖椾含");
        Student s4 = new Student(4L, "鏉庣幇", 17, "娴欐睙");
        List<Student> students = new ArrayList<>();
        students.add(s1);
        students.add(s2);
        students.add(s3);
        students.add(s4);
        boolean anyMatch = students.stream().anyMatch(s -> "婀栧寳".equals(s.getAddress()));
        if (anyMatch) {
            System.out.println("鏈夋箹鍖椾汉");
        }
        boolean allMatch = students.stream().allMatch(s -> s.getAge() >= 15);
        if (allMatch) {
            System.out.println("鎵€鏈夊鐢熼兘婊?5鍛ㄥ瞾");
        }
        boolean noneMatch = students.stream().noneMatch(s -> "鏉ㄦ磱".equals(s.getName()));
        if (noneMatch) {
            System.out.println("娌℃湁鍙潹娲嬬殑鍚屽");
        }
    }

涓婇潰浠嬬粛浜哠tream甯哥敤鐨勪竴浜涙柟娉曪紝铏界劧瀵归泦鍚堢殑閬嶅巻鍜屾搷浣滃彲浠ョ敤浠ュ墠甯歌鐨勬柟寮忥紝浣嗘槸褰撲笟鍔￠€昏緫澶嶆潅鐨勬椂鍊欙紝浣犱細鍙戠幇浠ｇ爜閲忓緢澶氾紝鍙鎬у緢宸紝鏄庢槑涓€琛屼唬鐮佽В鍐崇殑浜嬫儏锛屼綘鍗村啓浜嗗ソ鍑犺銆傝瘯璇昹ambda琛ㄨ揪寮忥紝璇曡瘯Stream锛屼綘浼氭湁涓嶄竴鏍风殑浣撻獙銆?/p>