Article directory
- method
- Practice Notes
-
- 1. Preconditions
- Two, operation
-
- maxBy: Get the largest element in the stream; minBy: Get the smallest element in the stream
- joining: Merge, join the elements in the stream in the form of strings
- summingInt: Map the elements in the stream to elements of type int, and sum
- averagingInt: Map the elements in the stream to elements of type int, and calculate the average value
- summarizingInt: Map the elements in the stream to elements of type int to obtain description information
method
● maxBy: Get the largest element in the stream; minBy: Get the smallest element in the
stream
. and
● averagingInt: maps the elements in the stream to int type elements, and calculates the average value
summarizingInt: maps the stream elements into int type elements, and obtains description information
Practice Notes
1. Preconditions
Person class
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 class
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;
}
}
Two, operation
maxBy: Get the largest element in the stream; minBy: Get the smallest element in the stream
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: Merge, join the elements in the stream in the form of strings
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: Map the elements in the stream to elements of type int, and sum
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: Map the elements in the stream to elements of type int, and calculate the average value
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: Map the elements in the stream to elements of type int to obtain description information
Requirement: Replace Person objects with scores greater than or equal to 80 in the stream with their names
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());
output result:
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