Java流式操作之Collectors工具类操作指南

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();

     }

}

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;

     }

}

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())));

}

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( "-" , "{" , "}" )));

}

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)));

}

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)));

}

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());