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:
