package com.example.jsch_smb;
import cn.hutool.core.collection.CollUtil;
import cn.hutool.core.map.MapUtil;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Java8StreamDemo {
//并行流 parallelStream forEachOrdered
? ? private void parallelStream() {
List nums = CollUtil.newArrayList(1, 2, 3, 4, 5);
? ? ? ? //順序打印
? ? ? ? nums.stream().forEach(System.out::print);
? ? ? ? nums.stream().forEachOrdered(System.out::print);
? ? ? ? //并行流
? ? ? ? nums.parallelStream().forEach(System.out::print);
? ? ? ? nums.parallelStream().forEachOrdered(System.out::print);
? ? }
//流連接 flatMap
? ? private void flatMap() {
List list = Arrays.asList("a,b,c", "1,2,3");
? ? ? ? List newList = list.stream().flatMap(s -> {
//將每個(gè)元素轉(zhuǎn)換成一個(gè)stream
? ? ? ? ? ? String[] split = s.split(",");
? ? ? ? ? ? Stream s2 = Arrays.stream(split);
? ? ? ? ? ? return s2;
? ? ? ? }).collect(Collectors.toList());
? ? ? ? newList.forEach(System.out::println); // a b c 1 2 3
? ? }
//分組排序 Comparator.comparing Comparator.naturalOrder Collectors.partitioningBy
? ? private void groupAndSort() {
Student s1 =new Student("aa", 10);
? ? ? ? Student s2 =new Student("bb", 20);
? ? ? ? Student s3 =new Student("aa",30);
? ? ? ? Student s4 =new Student("dd", 40);
? ? ? ? List students = CollUtil.newArrayList(s1, s2, s3, s4);
? ? ? ? //二次排序
? ? ? ? students.stream().sorted(
Comparator.comparing(Student::getName,Comparator.naturalOrder())
.thenComparing(Student::getAge,Comparator.reverseOrder())).collect(Collectors.toList());
? ? ? ? //一次分組 分成兩部分，一部分大于10歲伦腐，一部分小于等于10歲
? ? ? ? Map>> collect2 = students.stream().collect(
Collectors.partitioningBy(e -> e.getAge() >10, Collectors.groupingBy(Student::getName)));
? ? ? ? //二次分組? 先第一個(gè)提交 在第二個(gè)條件
? ? ? ? Map>> collect3 = students.stream().collect(
Collectors.partitioningBy(e -> e.getAge() >10, Collectors.groupingBy(k -> {
if (k.getAge() ==30) {
return "equal";
? ? ? ? ? ? ? ? ? ? }else {
return "unequal";
? ? ? ? ? ? ? ? ? ? }
})));
? ? ? ? //分組統(tǒng)計(jì)
? ? ? ? LinkedHashMap collect = students.stream().collect(
Collectors.groupingBy(Student::getName, LinkedHashMap::new, Collectors.counting()));
? ? ? ? //分組取最大值
? ? ? ? Map collect1 = students.stream().collect(
Collectors.groupingBy(Student::getName, Collectors.collectingAndThen(
Collectors.maxBy(Comparator.comparingInt(Student::getAge)), Optional::get)));
? ? }
//匹配,聚合
? ? private void match() {
List list = Arrays.asList(1, 2, 3, 4, 5);
? ? ? ? boolean allMatch = list.stream().allMatch(e -> e >10); //false
? ? ? ? boolean noneMatch = list.stream().noneMatch(e -> e >10); //true
? ? ? ? boolean anyMatch = list.stream().anyMatch(e -> e >4); //true
? ? ? ? Integer findFirst = list.stream().findFirst().get(); //1
? ? ? ? Integer findAny = list.stream().findAny().get(); //1
? ? ? ? long count = list.stream().count(); //5
? ? ? ? Integer max = list.stream().max(Integer::compareTo).get(); //5
? ? ? ? Integer min = list.stream().min(Integer::compareTo).get(); //1
? ? }
//積累
? ? private void experience() {
Student s1 =new Student("aa", 10);
? ? ? ? Student s2 =new Student("bb", 20);
? ? ? ? Student s3 =new Student("aa", 30);
? ? ? ? Student s4 =new Student("dd", 40);
? ? ? ? List students = CollUtil.newArrayList(s1, s2, s3, s4);
? ? ? ? // 1. 取max 值
//List
? ? ? ? IntSummaryStatistics collect = CollUtil.newArrayList(1, 2, 3, 4, 5).stream().collect(Collectors.summarizingInt(Integer::intValue));
? ? ? ? //IntSummaryStatistics{count=5, sum=15, min=1, average=3.000000, max=5}
// List
? ? ? ? students.stream().collect(Collectors.summarizingInt(Student::getAge)).getMax();
? ? ? ? // List
? ? ? ? List maps = CollUtil.newArrayList();
? ? ? ? students.parallelStream().forEach(e -> {
maps.add(MapUtil.of(e.getName(), e.getAge()));
? ? ? ? });
? ? ? ? maps.stream().mapToInt(
m -> m.get("age") !=null ? Integer.parseInt(m.get("age").toString()) :0
? ? ? ? ).max().getAsInt();
? ? ? ? // 2. 取總值 等聚合值 sum average ...
// List<對(duì)象>
? ? ? ? students.stream().mapToInt(n -> n.getAge()).summaryStatistics().getSum();
? ? ? ? // List
? ? ? ? int sum = maps.stream().mapToInt(
m -> m.get("age") !=null ? Integer.parseInt(m.get("age").toString()) :0
? ? ? ? ).sum();
? ? }
public static void main(String[] args) {
Java8StreamDemo demo =new Java8StreamDemo();
? ? ? ? demo.groupAndSort();
? ? }
static class Student {
private Stringname;
? ? ? ? private int age;
? ? ? ? public Student(String name, int age) {
this.name = name;
? ? ? ? ? ? this.age = age;
? ? ? ? }
public StringgetName() {
return name;
? ? ? ? }
public void setName(String name) {
this.name = name;
? ? ? ? }
public int getAge() {
return age;
? ? ? ? }
public void setAge(int age) {
this.age = age;
? ? ? ? }
}
}
