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Java流式操作之Collectors工具类操作指南

目录
  • 方法
  • 实践说明
    • 一、前提条件
    • 二、操作
  • 总结

    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开发者_JAVA入门;
            return this;
        }
        public int getScore() {
            return score;
        }
        public Person setScore(int score) {
            this.score = score;
            return this;
        }
        private String name;
        private int age;
        private inteNHaUV 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<>();
    php        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
        编程客栈    System.out.println(Data.getData().stream().collect(Collec编程客栈tors.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

    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(Swww.devze.comtring[] 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:

    Java流式操作之Collectors工具类操作指南

    总结

    到此这篇关于Java流式操作之Collectors工具类操作的文章就介绍到这了,更多相关Java流式操作Collectors工具类内容请搜索我们以前的文章或继续浏览下面的相关文章希望大家以后多多支持我们!

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