java8的Stream 流式操作，用于对集合进行投影、转换、过滤、排序、去重等，更进一步地说，这些操作能链式串联在一起使用，类似于 SQL 语句，可以大大简化代码。下面我就将平时常用的一些stream操作做一些汇总。
通过 IntStream 构造基本类型的流 //在java8之前，遍历0-99的基本操作 for(int i = 0;i<100;i++){ System.out.println("i:"+i); } //使用IntStream串行遍历 IntStream.rangeClosed(0,99).forEach(i->{ System.out.println("i:"+i); }); //使用IntStream并行遍历 IntStream.rangeClosed(0,99).parallel().forEach(i->{ System.out.println("i:"+i); }); 定义一个学生的结构体，为后续操作做准备 class Student{ private String name; private int age; private int score; private String city; public Student(String name, int age, int score, String city) { this.name = name; this.age = age; this.score = score; this.city = city; } 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 int getScore() { return score; } public void setScore(int score) { this.score = score; } public String getCity() { return city; } public void setCity(String city) { this.city = city; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Student student = (Student) o; return age == student.age && score == student.score && Objects.equals(name, student.name) && Objects.equals(city, student.city); } @Override public int hashCode() { return Objects.hash(name, age, score, city); } @Override public String toString() { return "Student{" + "name='" + name + '\'' + ", age=" + age + ", score=" + score + ", city='" + city + '\'' + '}'; } } //构造数据 List<Student> students = new ArrayList<>(); students.add(new Student("stu001",18,70,"合肥")); students.add(new Student("stu001",18,70,"合肥")); students.add(new Student("stu002",23,80,"郑州")); students.add(new Student("stu003",45,90,"郑州")); students.add(new Student("stu004",32,73,"合肥")); students.add(new Student("stu005",66,76,"南京")); students.add(new Student("stu006",34,79,"杭州")); students.add(new Student("stu007",28,90,"合肥")); students.add(new Student("stu008",19,100,"杭州")); filter根据特定的条件进行过滤
//filter 实现过滤操作，这边过滤出年龄大于30的学生 students.stream().filter(s->s.getAge()>30).forEach(System.out::println); map元素进行转化
//map 对流每一个元素进行转化，将student的age转化成流 students.stream().map(Student::getAge).forEach(System.out::println); sort 排序根据条件进行排序操作
//sort 按年龄排序，倒序 students.stream().sorted(Comparator.comparing(Student::getAge).reversed()).forEach(System.out::println); distinct 去重对流元素进行去重操作
//distinct 去重,因为实现了hashcode和equals，名称为stu001的学生重复了 students.stream().distinct().forEach(System.out::println); 将集合组成一个list students.stream().map(Student::getAge).collect(Collectors.toList()).forEach(System.out::println); 将集合组成一个set students.stream().map(Student::getAge).collect(Collectors.toSet()).forEach(System.out::println); 最大值求出年龄最大的学生
System.out.println(students.stream().max(Comparator.comparingInt(Student::getAge)).get()); 最大值求出年龄最最小的学生
System.out.println(students.stream().min(Comparator.comparingInt(Student::getAge)).get()); join操作按照逗号进行join,用[]包裹起来
//join操作，姓名join System.out.println(students.stream().map(Student::getName).collect(Collectors.joining(",","[","]"))); toMap操作根据指定key,value生成一个map
students.stream().collect(Collectors.toMap(Student::getName,student -> student,(x1,x2)->x2)).entrySet().forEach(System.out::println);