方法

● maxBy：获取流中最大元素；minBy：获取流中最小元素
● joining:合并，将流中的元素，以字符串的形式拼接起来
● summingInt:把流中的元素映射成int类型的元素，求和
● averagingInt:把流中的元素映射成int类型的元素，求平均值
● summarizingInt:把流中的元素映射成int类型的元素，获取描述信息

---

实践说明

一、前提条件

Person类

package com.example;

import lombok.AllArgsConstructor;
import lombok.Data;
import org.springframework.context.annotation.Configuration;

import java.util.Objects;

/**
 * @BelongsProject: StreamOperate
 * @BelongsPackage: com.example
 * @CreateTime: 2023-05-01  11:18
 * @Description: Person实体类
 * @Version: 1.0
 */
public class Person implements Comparable<Person>{
    public String getName() {
        return name;
    }

    public Person setName(String name) {
        this.name = name;
        return this;
    }

    public int getAge() {
        return age;
    }

    public Person setAge(int age) {
        this.age = age;
        return this;
    }

    public int getScore() {
        return score;
    }

    public Person setScore(int score) {
        this.score = score;
        return this;
    }

    private String name;
    private int age;
    private int score;


    public Person(String name, int age, int score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    public Person() {

    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", score=" + score +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        //地址相同，为true
        if (this == o) return true;
        //为null，并且类型不一样，为false
        if (o == null || getClass() != o.getClass()) return false;
        //向下转型，再去比较属性值
        Person person = (Person) o;
        //如果属性值相同，最后的结果为true
        return age == person.age && score == person.score && Objects.equals(name, person.name);


        //return false;
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age, score);
    }


    @Override
    public int compareTo(Person o) {
        return this.getScore()-o.getScore();
    }
}

Data类

package com.example;

import org.springframework.context.annotation.Configuration;

import java.util.ArrayList;

/**
 * @BelongsProject: StreamOperate
 * @BelongsPackage: com.example
 * @CreateTime: 2023-05-01  11:08
 * @Description: Data类
 * @Version: 1.0
 */
public class Data {
    public static ArrayList<Person> getData() {
        ArrayList<Person> personList = new ArrayList<>();

        personList.add(new Person("张三", 18, 90));
        personList.add(new Person("李四", 19, 100));
        personList.add(new Person("王五", 17, 60));
        personList.add(new Person("赵六", 18, 89));
        personList.add(new Person("孙七", 20, 96));
        personList.add(new Person("郑十", 20, 46));
        personList.add(new Person("周八", 20, 96));
        personList.add(new Person("周八", 20, 96));
        personList.add(new Person("吴九", 20, 45));
        personList.add(new Person("邓十一", 20, 35));
        personList.add(new Person("刘十二", 20, 99));
        personList.add(new Person("小十三", 20, 56));
        personList.add(new Person("小十三", 20, 56));

        return personList;
    }
}

---

二、操作

maxBy：获取流中最大元素；minBy：获取流中最小元素

public static void main(String[] args) {
        Stream<Person> stream = Data.getData().stream();

        //maxBy：获取流中最大元素；minBy：获取流中最小元素
        System.out.println(Data.getData().stream().collect(Collectors.maxBy((ele1, ele2) -> ele1.getScore() - ele2.getScore())));
        System.out.println(Data.getData().stream().collect(Collectors.minBy((ele1, ele2) -> ele1.getAge() - ele2.getAge())));
}

---

joining:合并，将流中的元素，以字符串的形式拼接起来

去public static void main(String[] args) {
        Stream<Person> stream = Data.getData().stream();

        //joining:合并，将流中的元素，以字符串的形式拼接起来
        //将集合中person对象的姓名拼接成一个字符串
        System.out.println(Data.getData().stream().map(Person::getName).collect(Collectors.joining()));
        System.out.println(Data.getData().stream().map(Person::getName).collect(Collectors.joining("-")));
        System.out.println(Data.getData().stream().map(Person::getName).collect(Collectors.joining("-", "{", "}")));
}

---

summingInt:把流中的元素映射成int类型的元素，求和

public static void main(String[] args) {
        Stream<Person> stream = Data.getData().stream();
				
				//summingInt:把流中的元素映射成int类型的元素，求和
        System.out.println(Data.getData().stream().collect(Collectors.summingInt(Person::getScore)));
}

---

averagingInt:把流中的元素映射成int类型的元素，求平均值

public static void main(String[] args) {
        Stream<Person> stream = Data.getData().stream();

        //averagingInt:把流中的元素映射成int类型的元素，求平均值
        System.out.println(Data.getData().stream().collect(Collectors.averagingInt(Person::getScore)));
}

---

summarizingInt:把流中的元素映射成int类型的元素，获取描述信息

需求：将流中分数大于等于80的Person对象替换成他们的姓名

 public static void main(String[] args) {
        Stream<Person> stream = Data.getData().stream();
      
        //summarizingInt:把流中的元素映射成int类型的元素，获取描述信息
        IntSummaryStatistics collect = Data.getData().stream().collect(Collectors.summarizingInt(Person::getScore));
        System.out.println(collect);
        System.out.println(collect.getCount());
        System.out.println(collect.getSum());
        System.out.println(collect.getMax());
        System.out.println(collect.getMax());
        System.out.println(collect.getAverage());

输出结果:

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