java集合操作-Lambda表达式

需要引包：

    compile group: 'com.google.guava', name: 'guava', version: '28.1-jre'

 

package com.zhuzhuxia.demo;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONArray;
import com.google.common.collect.Lists;
import org.junit.jupiter.api.Test;

import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

/**
 * @Author: 猪猪侠
 * @Date: 2019/10/30 17:59
 * @Version: 1.0
 * @Description:
 */
public class MyTest {

    @Test
    public void listTest(){
        List integerList = Lists.newArrayList(1, 2, 3, 4, 5, 6, 3, 5, 1, 4, 2, 8, 9);
        List studentList = Lists.newArrayList();
        Student stu1 = new Student(1L,"张三",15);
        Student stu2 = new Student(2L,"李四",11);
        Student stu3 = new Student(3L,"王五",12);
        Student stu4 = new Student(4L,"赵六",10);
        studentList.add(stu1);
        studentList.add(stu2);
        studentList.add(stu3);
        studentList.add(stu4);
        System.out.println("学生原数据："+JSONArray.toJSON(studentList));
        System.out.println("-----------------------------------------------------");


        List 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 collect2 = studentList.stream().map(stu -> stu.getAge()).collect(Collectors.toList());
        System.out.println("取出学生的年龄集合："+collect2);

        List 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 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 collect4 = studentList.stream().limit(3).collect(Collectors.toList());
        System.out.println("学生集合里取前三个："+JSONArray.toJSON(collect4));

        Map> 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));




    }


    public static class Student{
        private Long id;
        private String name;
        private Integer age;

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

        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 Integer getAge() {
            return age;
        }

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

}

运行结果：

学生原数据：[{"name":"张三","id":1,"age":15},{"name":"李四","id":2,"age":11},{"name":"王五","id":3,"age":12},{"name":"赵六","id":4,"age":10}]
-----------------------------------------------------
查出姓名是“张三”的学生：[{"name":"张三","id":1,"age":15}]
取出学生的年龄集合：[15, 11, 12, 10]
取出学生的年龄集合并去重：[15, 11, 12, 10]
学生集合里去除前三个：[{"name":"赵六","id":4,"age":10}]
学生集合里取前三个：[{"name":"张三","id":1,"age":15},{"name":"李四","id":2,"age":11},{"name":"王五","id":3,"age":12}]
根据学生年龄分组：{"11":[{"name":"李四","id":2,"age":11}],"12":[{"name":"王五","id":3,"age":12}],"15":[{"name":"张三","id":1,"age":15}],"10":[{"name":"赵六","id":4,"age":10}]}
找出学生年龄之和：48
找出学生年龄最大：15
找出学生年龄最小：10
找出学生年龄最小：12.0
根据学生年龄降序：[{"name":"张三","id":1,"age":15},{"name":"王五","id":3,"age":12},{"name":"李四","id":2,"age":11},{"name":"赵六","id":4,"age":10}]
根据学生年龄升序：[{"name":"赵六","id":4,"age":10},{"name":"李四","id":2,"age":11},{"name":"王五","id":3,"age":12},{"name":"张三","id":1,"age":15}]