import org.junit.Test;
import java.text.SimpleDateFormat;
import java.util.*;
import java.util.stream.Collectors;
import static java.util.Comparator.comparingLong;
import static java.util.stream.Collectors.*;
/**
* @Author:
* @www.1b23.com
* @Description:
*/
public class test {
public static void main(String[] args) {
List<User> list = new ArrayList<>();
list.add(new User(21L, "张三"));
list.add(new User(25L, "李四"));
list.add(new User(22L, "王五"));
list.add(new User(19L, "赵柳"));
list.add(new User(32L, "王5"));
list.add(new User(29L, "王6"));
list.add(new User(21L, "王7"));
// 对象根据年龄属性升序排序
List<User> newList = list.stream().sorted(Comparator.comparing(User::getAge)).collect(toList());
// 对象根据年龄属性降序排序
List<User> newList = list.stream().sorted(Comparator.comparing(User::getAge).reversed()).collect(toList());
// 标识升序，再按创建日期降序
// List<BhAnnouncement> newList = announcementList.stream().sorted(Comparator.comparing(BhAnnouncement::getReadFlag).thenComparing(BhAnnouncement::getSendTime).reversed()).collect(toList());
// list遍历
newList.forEach(System.out::println);
// 平均数
double asDouble = list.stream().mapToLong(User::getAge).average().getAsDouble();
System.out.println("average:" + asDouble);
double avg = list.stream().collect(Collectors.averagingLong(User::getAge));
System.out.println("average:" + avg);
// 最大值
long asLong = list.stream().mapToLong(User::getAge).max().getAsLong();
System.out.println("max:" + asLong);
// 最小值
long asLong1 = list.stream().mapToLong(User::getAge).min().getAsLong();
System.out.println("min:" + asLong1);
// 求和
long sum1 = list.stream().mapToLong(User::getAge).sum();
System.out.println("sum:" + sum1);
// 提取对象属性生成list
List<Long> ids = list.stream().map(User::getAge).collect(toList());
System.out.println(ids);
// list升序排序
Collections.sort(ids);
System.out.println(ids);
// 生成中位数
Long j;
if (ids.size() % 2 == 0) {
j = (ids.get(ids.size() / 2 - 1) + ids.get(ids.size() / 2)) / 2;
System.out.println("中位数为" + j);
} else {
j = ids.get(ids.size() / 2);
System.out.println("中位数为" + j);
}
// list倒序排序
ids.sort(Comparator.reverseOrder());
System.out.println(ids);
// 去重
List<User> users = list.stream().collect(collectingAndThen(toCollection(() -> new TreeSet<>(comparingLong(User::getAge))), ArrayList::new));
System.out.println("去重:"+users);
/**
* List -> Map
* 需要注意的是：toMap 如果集合对象有重复的key，会报错Duplicate key ....
* apple1,apple12的id都为1。可以用 (k1,k2)->k1 来设置，如果有重复的key,则保留key1,舍弃key2
*/
Map<Long, User> userMap = list.stream().collect(Collectors.toMap(User::getAge, a -> a, (k1, k2) -> k1));
System.out.println(userMap);
//过滤出符合条件的数据
List<User> filterList = list.stream().filter(a -> a.getName().equals("李四")).collect(toList());
System.out.println("filterList:" + filterList);
List<Integer> list2 = Arrays.asList(1, 2, 3, 4, 5);
int sum = list2.stream().reduce(0, (acc, value) -> acc + value);
System.out.println(sum);
List<Integer> result = list2.stream().filter((value) -> value > 2).collect(toList());
result.forEach(System.out::println);
List<String> result2 = list2.stream().map(value -> String.format("String:%s", value)).collect(toList());
result2.forEach(System.out::println);
// 用于收集统计数据的状态对象，例如count，min，max，sum和平均。
IntSummaryStatistics stats = list2.stream().mapToInt((x) -> x).summaryStatistics();
System.out.println("Max : " + stats.getMax());
System.out.println("Min: " + stats.getMin());
System.out.println("Sun: " + stats.getSum());
System.out.println("Average : " + stats.getAverage());
System.out.println("Count : " + stats.getCount());
System.out.println("toString : " + stats.toString());
}
}
class User {
private Long age;
private String name;
public User(Long i, String s) {
this.age = i;
this.name = s;
}
public Long getAge() {
return age;
}
public void setAge(Long age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "User [age=" + age + ", name=" + name + "]";
}
}
