java8+ Lambda表达式基本用法

LIST

public class LambdaTest {

    @Getter
    @Setter
    @AllArgsConstructor
    static class Student{
        private Long id;
        private String name;
        private Integer age;
    }

    public static void main(String[] args) {
        List<Student> studentList = Arrays.asList(new Student(1L,"张三",15),new Student(2L,"李四",11),
                new Student(3L,"王五",12),new Student(4L,"赵六",10));
        System.out.println("原数据："+ JSONArray.toJSON(studentList));
        List<Student> collect1 = studentList.stream().filter(stu -> stu.getName().equals("张三")).collect(Collectors.toList());
        System.out.println("查出姓名是张三的学生："+JSONArray.toJSON(collect1));
        List<Integer> collect2 = studentList.stream().map(stu -> stu.getAge()).collect(Collectors.toList());
        System.out.println("取出学生的年龄集合："+collect2);
        List<Integer> collect6 = studentList.stream().map(stu -> stu.getAge()).distinct().collect(Collectors.toList());
        System.out.println("取出学生的年龄集合并去重："+collect6);
        List<Student> collect3 = studentList.stream().skip(3).collect(Collectors.toList());
        System.out.println("学生集合里去除前三个："+JSONArray.toJSON(collect3));
        List<Student> collect4 = studentList.stream().limit(3).collect(Collectors.toList());
        System.out.println("学生集合里取前三个："+JSONArray.toJSON(collect4));
        Map<Integer, List<Student>> collect5 = studentList.stream().collect(Collectors.groupingBy(student -> student.getAge()));
        System.out.println("根据学生年龄分组："+JSONArray.toJSON(collect5));
        int ageSum = studentList.stream().mapToInt(stu -> stu.getAge()).sum();
        System.out.println("找出学生年龄之和："+ageSum);
        int ageMax= studentList.stream().mapToInt(stu -> stu.getAge()).max().getAsInt();
        System.out.println("找出学生年龄最大："+ageMax);
        int ageMin= studentList.stream().mapToInt(stu -> stu.getAge()).min().getAsInt();
        System.out.println("找出学生年龄最小："+ageMin);
        Double aggAverage = studentList.stream().mapToInt(stu -> stu.getAge()).average().getAsDouble();
        System.out.println("找出学生年龄最小："+aggAverage);
        studentList.sort((a,b) -> b.getAge().compareTo(a.getAge()));
        System.out.println("根据学生年龄降序："+JSONArray.toJSON(studentList));
        studentList.sort((a,b) -> a.getAge().compareTo(b.getAge()));
        System.out.println("根据学生年龄升序："+JSONArray.toJSON(studentList));
    }

}

转逗号分隔

list.stream().collect(Collectors.joining(","))

排序

升序

studentList.sort(Comparator.comparing(Student::getAge));

降序

studentList.sort(Comparator.comparing(Student::getAge).reversed());

分组

根据传入的size将现有list分组（分页）

public static <T> List<List<T>> splitList(List<T> in, int size){
        List<List<T>> out = new ArrayList<>();
        int mode = in.size()%size;
        int page = in.size()/size;
        for(int i=1;i<=page;i ++){
            int start = (i-1)*size;
            List<T> sub = in.subList(start,start+size);
            out.add(sub);
        }
        if(mode>0){
            int start = page*size;
            List<T> sub = in.subList(start,start+mode);
            out.add(sub);
        }
        return out;
    }