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Java8lambda排序筛选分组求和最大值平均值

Java8lambda排序筛选分组求和最⼤值平均值

在⼯作中发现Java8使⽤很普遍，整理⼯作中常⽤的Java8集合语法。

package cc.pigg.base.study.stream;

import lombok.AllArgsConstructor;

import lombok.Data;

import java.util.*;

import java.util.stream.Collectors;

public class JavaStreamTest {

private static List<Person> personList =new ArrayList<>();

public static void main(String[] args){

personList.add(new Person(1L ,"猪爸爸",30,"男"));

personList.add(new Person(2L ,"猪妈妈",28,"⼥"));

personList.add(new Person(3L ,"佩奇",5,"⼥"));

personList.add(new Person(4L ,"乔治",2,"男"));

System.out.println("hello");

System.out.println("===foreach循环===");

for(Person person : personList){

System.out.String());

}

System.out.println("===Java8的foreach()===");

personList.forEach(person -> System.out.String()));

System.out.println("===foreach()年龄都加1岁===");

personList.forEach(p -> p.Age()+1));

print();

System.out.println("===map toList===");

//获取id的List集合

List<Long> ids = personList.stream().map(Person::getId).List());

ids.forEach(id -> System.out.println(id));

System.out.println("===map toSet===");

//获取性别的Set集合

Set<String> genders = personList.stream().map(Person::getGender).Set());

genders.forEach(gender -> System.out.println(gender));

System.out.println("===获取名称以逗号分隔===");

String names = personList.stream().map(Person::getName).collect(Collectors.joining(","));

固液分离装置System.out.println(names);

System.out.println("===List 转 Map<Long, Person> 根据ID分组===");

//如果ID重复就⽤第⼀个

Map<Long, Person> mapById = personList.stream().Map(Person::getId, a -> a,(k1, k2)-> k1));

mapById.forEach((key, value)-> System.out.println(key +" -> "+ String()));

System.out.println("===List 转 Map<String, Person> 根据gender分组===");

空调连接管

//如果gender重复就⽤第⼀个

Map<String, Person> mapByGender = personList.stream().Map(Person::getGender, a -> a,(k1, k2)-> k1)); mapByGender.forEach((key, value)-> System.out.println(key +" -> "+ String()));

System.out.println("===List 转 Map<String, List<Person>> 根据gender分组===");

Map<String, List<Person>> groupByGender = personList.stream().upingBy(Person::getGender));

groupByGender.forEach((key, value)-> System.out.println(key +" -> "+ String()));

System.out.println("===统计值===");

//最⼤年龄

Integer maxAge = personList.stream().mapToInt(Person::getAge).max().getAsInt();

束身带//最⼩年龄

Integer minAge = personList.stream().mapToInt(Person::getAge).min().getAsInt();

//年龄求和

pigg

Integer sumAge = personList.stream().mapToInt(Person::getAge).sum();

//平均年龄

Double avgAge = personList.stream().mapToInt(Person::getAge).average().getAsDouble();

System.out.println("maxAge = "+ maxAge);

System.out.println("minAge = "+ minAge);

System.out.println("sumAge = "+ sumAge);

System.out.println("avgAge = "+ avgAge);

System.out.println("===List<Integer> 的最⼤值===");

System.out.println("最⼤的ID="+ Collections.max(ids));

商场柜台制作System.out.println("===SummaryStatistics统计===");

IntSummaryStatistics iss = personList.stream().mapToInt(Person::getAge).summaryStatistics();

System.out.println("max = "+ Max());

System.out.println("min = "+ Min());

System.out.println("sum = "+ Sum());

System.out.println("avg = "+ Average());

System.out.println("===分组统计利⽤SummaryStatistics===");

//求不同性别的平均年龄

Map<String, IntSummaryStatistics> genderSummary =

personList.stream().upingBy(Person::getGender, Collectors.summarizingInt(Person::getAge)));

山药开沟机

genderSummary.forEach((k, v)-> System.out.println(k +" -> 最⼤年龄="+ v.getMax()+", 平均年龄="+ v.getAverage()+", ⼈数="+ v.getCount()));

System.out.println("===分组统计数量===");

//求不同性别的⼈数

Map<String, Long> genderSummary2 =

personList.stream().upingBy(Person::getGender, unting()));

genderSummary2.forEach((k, v)-> System.out.println(k +" -> ⼈数="+ v));

System.out.println("===filter 筛选出成⼈男===");

List<Person> mans = personList.stream().filter(person ->"男".Gender())&& Age()>=18).List()); mans.forEach(person -> System.out.String()));

System.out.println("===Comparator 根据年龄升序排===");

personList.sort(Comparatorparing(Person::getAge));

print();

System.out.println("===Comparator 根据ID降序排===");

personList.sort(Comparatorparing(Person::getId).reversed());

print();

System.out.println("===Comparator 组合排序===");

personList.sort(Comparatorparing(Person::getGender).thenComparing(Person::getAge));

print();

System.out.println("goodbye");

}

private static void print(){

personList.forEach(person -> System.out.String()));

}

@Data

@AllArgsConstructor

class Person {

private Long id;

private String name;

private Integer age;

private String gender;

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标签：分组获取求和筛选排序集合

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