什么是Stream？

也叫Stream流，是jdk8开始新增的一套API，可以用来操作集合或者数组的数据

优势：Stream流大量的结合了Lambda的语法风格来编程，提供了一种更加强大，更加简单的方式操作集合或数组中的数据，代码更简洁，可读性更好

import java.util.*;
import java.util.stream.Collectors;public class Work1 {public static void main(String[] args) {List<String> names = new ArrayList<>();names.add("温小辉");names.add("小朱");names.add("简隋英");names.add("邵群");names.add("小白");System.out.println(names);//找出带小的名字，存入新的集合中去List<String> list = new ArrayList<>();for (String name : names) {if (name.contains("小")&&name.length()==2){list.add(name);}}System.out.println(list);//开始使用Stream流List list1 = names.stream().filter(s->s.contains("小")).filter(a->a.length()==2).collect(Collectors.toList());System.out.println(list1);}
}

1，如何获取集合和数组的Stream流？

import java.util.*;
import java.util.stream.Stream;public class Work1 {public static void main(String[] args) {//1,如何获取List集合的Stream流？List<String> names = new ArrayList<>();Collections.addAll(names,"温小辉","小朱","简隋英","邵群","小白");Stream<String> stream = names.stream();//2,如何获取Set集合的Stream流？Set<String> set = new HashSet<>();Collections.addAll(set,"李玉","李程秀","兰波","白新羽","何故");Stream<String> stream1 = set.stream();stream1.filter(s -> s.contains("李")).forEach(s -> System.out.println(s));//3,如何获取Map集合的Stream流?Map<String,Double>map = new HashMap<>();map.put("娘娘腔",9.5);map.put("你却爱着一个SB",9.9);map.put("人鱼陷落",9.8);map.put("附加遗产",9.6);//键流final Set<String> keys = map.keySet();final Stream<String> ks = keys.stream();//值流final Collection<Double> values = map.values();final Stream<Double> vs = values.stream();//键值对流final Set<Map.Entry<String, Double>> entries = map.entrySet();final Stream<Map.Entry<String, Double>> kvs = entries.stream();kvs.filter(e->e.getKey().contains("人")).forEach(e->System.out.println(e.getKey()+"-->"+e.getValue()));String[] names2 = {"言逸","陆上锦","陆言","毕揽星","百刃"};final Stream<String> s1 = Arrays.stream(names2);final Stream<String> s2 = Stream.of(names2);}
}

2，Stream流的常用方法

import java.util.*;
import java.util.stream.Stream;public class Work1 {public static void main(String[] args) {//需求一：找出成绩大于等于60分的数据，并升序后，再输出List<Double> scores = new ArrayList<>();Collections.addAll(scores, 88.5,100.0,60.0,99.0,9.5,99.6,25.0);scores.stream().filter(s->s>=60).sorted().forEach(s-> System.out.println(s));List<Student> students = new ArrayList<>();Student s1 = new Student("简隋英",32,188);Student s2 = new Student("简隋英",32,188);Student s3 = new Student("邵群",31,189);Student s4 = new Student("洛羿",19,187);Student s5 = new Student("李玉",21,188.5);Student s6 = new Student("白新羽",22,185.2);Student s7 = new Student("何故",25,183);Collections.addAll(students,s1,s2,s3,s4,s5,s6,s7);//找出年龄大于等于20且小于等于30，并按照年龄降序输出students.stream().filter(s->s.getAge()>=20 &&s.getAge()<=30).sorted(((o1, o2) -> o2.getAge()- o1.getAge())).forEach(s-> System.out.println(s));System.out.println(".....................................");//取出身高最高的前三名students.stream().sorted(((o1, o2) -> Double.compare(o2.getHeight(), -o1.getHeight()))).limit(3).forEach(s-> System.out.println(s));System.out.println("......................................");//取出身高最矮的两名students.stream().sorted(((o1, o2) -> Double.compare(o2.getHeight(), -o1.getHeight()))).skip(students.size()-2).forEach(s-> System.out.println(s));//找出身高超过188的叫什么名字，要求去掉重复的名字，再输出//distinct去重复，自定义类型的对象(希望内容一样就认为重复，重写hashCode和equals方法)students.stream().filter(s->s.getHeight()>=188).map(s->s.getName()).distinct().forEach(s -> System.out.println(s));final Stream<String> st1 = Stream.of("张三", "王五");final Stream<String> st2 = Stream.of("张三1", "王五2");final Stream<Object> allSt = Stream.concat(st1, st2);allSt.forEach(s-> System.out.println(s));}}

class Student{private String name;private int age;private double height;public Student() {}public Student(String name, int age, double height) {this.name = name;this.age = age;this.height = height;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public double getHeight() {return height;}public void setHeight(double height) {this.height = height;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", age=" + age +", height=" + height +'}';}
}

3，Stream流常见的终结方法

import java.util.*;
import java.util.stream.Collectors;public class Work1 {public static void main(String[] args) {List<Student> students = new ArrayList<>();Student s1 = new Student("简隋英",32,188);Student s2 = new Student("邵群",31,189);Student s3 = new Student("洛羿",19,187);Student s4 = new Student("李玉",21,188.5);Student s5 = new Student("白新羽",22,185.2);Student s6 = new Student("何故",25,183);Collections.addAll(students,s1,s2,s3,s4,s5,s6);//找出身高超过188的并输出final long size = students.stream().filter(s -> s.getHeight() > 188).count();System.out.println(size);//取出身高最高的并输出final Student s = students.stream().max((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight())).get();System.out.println(s);//取出身高最矮的两名Student ss = students.stream().min((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight())).get();System.out.println(ss);//找出身高超过185的，并放到一个新集合中去返回List <Student> students1 = students.stream().filter(a->a.getHeight()>185).collect(Collectors.toList());System.out.println(students1);//找出身高超过185的，并把对象的姓名和身高放到Map集合中去返回Map<String,Double> map = students.stream().filter(a->a.getHeight()>185).collect(Collectors.toMap(a->a.getName(),a->a.getHeight()));System.out.println(map);//放在数组中去Object[] arr = students.stream().filter(a -> a.getHeight() > 185).toArray();System.out.println(Arrays.toString(arr));}
}