[大数据]Stream流分组相关

  //使用Stream流对一个集合按照年龄进行分组
    @Test
    public void streamDemo05(){
        List<Teacher> teacherList = new ArrayList<>();
        teacherList.add(new Teacher(1L, "张三", 20));
        teacherList.add(new Teacher(2L, "张三", 23));
        teacherList.add(new Teacher(3L, "李四", 21));
        teacherList.add(new Teacher(4L, "王五", 21));
        teacherList.add(new Teacher(5L, "赵六", 24));
        //按照年龄分组
        Map<Integer, List<Teacher>> groupTeacherMap = teacherList.stream().collect(Collectors.groupingBy(Teacher::getAge));

        
        System.out.println(groupTeacherMap.get(21));
        /**结果：
         * [Teacher(id=3, name=李四, age=21), Teacher(id=4, name=王五, age=21)]
         */
    }