ListStreamTest.java
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package com.huaheng.test;
import com.google.common.collect.Lists;
import lombok.AllArgsConstructor;
import lombok.Data;
import java.util.Comparator;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import static java.util.stream.Collectors.*;
public class ListStreamTest {
public static void main(String[] args) {
List<Student> list = Lists.newArrayList();
list.add(new Student("测试", "男", 18));
list.add(new Student("开发", "男", 20));
list.add(new Student("运维", "女", 19));
list.add(new Student("DBA", "女", 22));
list.add(new Student("运营", "男", 24));
list.add(new Student("产品", "女", 21));
list.add(new Student("经理", "女", 25));
list.add(new Student("产品", "女", 21));
//求性别为男的学生集合
List<Student> l1 = list.stream().filter(student -> student.sex.equals("男")).collect(toList());
System.out.println(l1);
//map的key值true为男，false为女的集合
Map<Boolean, List<Student>> map = list.stream().collect(partitioningBy(student -> student.getSex().equals("男")));
System.out.println(map);
//求性别为男的学生总岁数
Integer sum = list.stream().filter(student -> student.sex.equals("男")).mapToInt(Student::getAge).sum();
System.out.println(sum);
//按性别进行分组统计人数
Map<String, Integer> map1s = list.stream().collect(Collectors.groupingBy(Student::getSex, Collectors.summingInt(p -> 1)));
System.out.println(map1s);
//判断是否有年龄大于25岁的学生
boolean check = list.stream().anyMatch(student -> student.getAge() > 25);
System.out.println(check);
//获取所有学生的姓名集合
List<String> l2 = list.stream().map(Student::getName).collect(toList());
System.out.println(l2);
//求所有人的平均年龄
double avg = list.stream().collect(averagingInt(Student::getAge));
System.out.println(avg);
//求年龄最大的学生
Student s = list.stream().reduce((student, student2) -> student.getAge() > student2.getAge() ? student:student2).get();
System.out.println(s);
Student stu = list.stream().collect(maxBy(Comparator.comparing(Student::getAge))).get();
System.out.println(stu);
//按照年龄从小到大排序
List<Student> l3 = list.stream().sorted((s1, s2) -> s1.getAge().compareTo(s2.getAge())).collect(toList());
System.out.println(l3);
//求年龄最小的两个学生
List<Student> l4 = l3.stream().limit(2).collect(toList());
System.out.println(l4);
//获取所有的名字，组成一条语句
String str = list.stream().map(Student::getName).collect(Collectors.joining(",", "[", "]"));
System.out.println(str);
//获取年龄的最大值、最小值、平均值、求和等等
IntSummaryStatistics intSummaryStatistics = list.stream().mapToInt(Student::getAge).summaryStatistics();
System.out.println(intSummaryStatistics.getMax());
System.out.println(intSummaryStatistics.getCount());
}
@Data
@AllArgsConstructor
static class Student{
String name;
String sex;
Integer age;
}
}