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
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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
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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
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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
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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
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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
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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
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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:
总结
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原文链接:https://blog.csdn.net/weixin_43319713/article/details/130462745