//集合创建流Stream<Student> stream1 = studentList.stream();//Stream静态方法创建流Stream<Student> stream2 = Stream.of(new Student(1, "张三", 12, 69),new Student(2, "李四", 12, 78.5),new Student(3, "王五", 13, 95),new Student(4, "赵六", 14, 23),new Student(5, "孙七", 11, 55.5));//数组创建流Stream<Student> stream = Arrays.stream(new Student[]{});

        //filter过滤年龄大于12的
        studentList.stream().filter(student -> student.getAge() > 12).forEach(System.out::println);System.out.println("--------------");//distinct去重
        studentList.stream().distinct().forEach(System.out::println);System.out.println("--------------");//过滤之后取前2，有点类似mysql的limit了,// limit取值找到符合条件的就结束了 不会继续查找所有，下面的输出语句只会执行2次，因为前面两个就是满足条件的
        studentList.stream().filter((student) -> {System.out.println("执行过滤");return student.getAge() >= 12;}).limit(2).forEach(System.out::println);System.out.println("--------------");//skip跳过满足条件前两个
        studentList.stream().filter(student ->  student.getAge() >= 12).skip(2).forEach(System.out::println);

    public void testStream2() {//将map中的函数应用到每个元素上，生成一个新的元素，也就是收集每个student的名字组成一个新的元素
        studentList.stream().distinct().map(student -> student.getName()).forEach(System.out::println);System.out.println("--------");//调用creatStream方法将每个Student对象都转换成一个流，然后flatMap将每个流汇总成一个流
        studentList.stream().distinct().flatMap(StreamTest::creatStream).forEach(System.out::println);}public static Stream<Student> creatStream(Student student){return Stream.of(student);}

 　　　　//allMatch(Predicate p) 检查是否匹配所有元素 是否所有student age > 12boolean result = studentList.stream().allMatch(student -> student.getAge() > 12);System.out.println(result);//anyMatch(Predicate p) 检查是否至少匹配一个元素result = studentList.stream().anyMatch(student -> student.getAge() == 12);System.out.println(result);//noneMatch(Predicate p) 检查是否没有匹配所有元素result = studentList.stream().noneMatch(student -> student.getAge() < 11);System.out.println(result);//findFirst() 从流的操作中返回第一个元素(封装在Optional中)//按score升序 之后取第一个Student student = studentList.stream().sorted((student1, student2) -> Double.compare(student1.getScore(), student2.getScore())).findFirst().get();System.out.println(student);student = studentList.stream().findAny().get();System.out.println(student);

        //累加，将流中元素进行求和List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);Integer sum = list.stream().reduce(0, (x, y) -> x + y);System.out.println(sum);//求student的总分Double allScore = studentList.stream().map(student -> student.getScore()).reduce(Double::sum).get();System.out.println(allScore);

        List<Student> studentList = Arrays.asList(new Student(1, "张三", 12, 69, Student.Clazz.Clazz2),new Student(2, "李四", 12, 78.5,Student.Clazz.Clazz2),new Student(3, "王五", 13, 95, Student.Clazz.Clazz3),new Student(4, "赵六", 14, 23, Student.Clazz.Clazz3),new Student(5, "孙七", 11, 55.5, Student.Clazz.Clazz1),new Student(5, "孙七", 11, 55.5, Student.Clazz.Clazz1));//toList() 收集到List集合中List<String> nameList = studentList.stream().map(student -> student.getName()).collect(Collectors.toList());System.out.println(nameList);//toSet() 收集到Set集合中 自动去重 默认返回的HashSetSet<String> nameSet= studentList.stream().map(student -> student.getName()).collect(Collectors.toSet());System.out.println(nameSet);System.out.println(nameSet.getClass());//返回指定集合类型TreeSet<String> nameTreeSet= studentList.stream().map(student -> student.getName()).collect(Collectors.toCollection(TreeSet::new));System.out.println(nameTreeSet.getClass());//分组groupingBy 返回map集合 类似sql group by了//根据年级分组Map<Student.Clazz, List<Student>> map = studentList.stream().collect(Collectors.groupingBy(Student::getClazz));System.out.println(map);//多次分组//先按年级再按年龄Map<Student.Clazz, Map<Integer, List<Student>>> map2 = studentList.stream().collect(Collectors.groupingBy(Student::getClazz, Collectors.groupingBy(Student::getAge)));System.out.println(map2);//分区partitioningBy 入参是个断言型接口
        studentList.stream().collect(Collectors.partitioningBy((student) -> student.getScore() >= 60));//summarizingDouble 对某个值进行 数据统计输出//对score进行统计DoubleSummaryStatistics statistics = studentList.stream().collect(Collectors.summarizingDouble(Student::getScore));statistics.getAverage();statistics.getCount();statistics.getMax();statistics.getMin();statistics.getSum();

    private int id;private String name;private int age;private double score;private Clazz clazz;public Student(String name) {this.name = name;}public Student(int id, String name, int age, double score) {this.id = id;this.name = name;this.age = age;this.score = score;}public Student(int id, String name, int age, double score, Clazz clazz) {this.id = id;this.name = name;this.age = age;this.score = score;this.clazz = clazz;}public int getId() {return id;}public void setId(int 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 double getScore() {return score;}public void setScore(double score) {this.score = score;}public Clazz getClazz() {return clazz;}public void setClazz(Clazz clazz) {this.clazz = clazz;}public String show() {return "测试方法引用";}@Overridepublic int hashCode() {final int prime = 11;int hashCode = 1;hashCode = prime * hashCode + age;hashCode = prime * hashCode + id;hashCode = prime * hashCode + ((name == null) ? 0 : name.hashCode());long temp;temp = Double.doubleToLongBits(score);hashCode = prime * hashCode + (int) (temp ^ (temp >>> 32));return hashCode;}@Overridepublic boolean equals(Object obj) {if (this == obj) {return true;}if (obj == null) {return false;}if (getClass() != obj.getClass()) {return false;}Student other = (Student) obj;if (age != other.age) {return false;}if (id != other.id) {return false;}if (name == null) {if (other.name != null) {return false;}} else if (!name.equals(other.name)) {return false;}if (Double.doubleToLongBits(score) != Double.doubleToLongBits(other.score)) {return false;}return true;}@Overridepublic String toString() {return "[id=" + id + ", name=" + name + ", age=" + age + ", score=" + score + ", Class=" + clazz + "]";}public static enum Clazz{Clazz1,Clazz2,Clazz3,}