JDK8新特性：Stream流

目录

1.获取Stream流

2.Stream流常见的中间方法

3.Stream流常见的终结方法

1、 Stream 是什么？有什么作用？结合了什么技术？
●也叫 Stream 流，是Jdk8开始新增的一套 API ( java . util . stream .*)，可以用于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者数组中的数据，代码更简洁，可读性更好。
2、说说 Stream 流处理数据的步骤是什么？

package com.xinbao.d8_stream;import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;public class StreamTest1 {public static void main(String[] args) {List<String> names = new ArrayList<>();Collections.addAll(names,"张三丰", "张无忌", "周芷若", "赵敏", "张强");System.out.println(names);//找出姓张且是三个字的名字，存到新集合中去List<String> list = new ArrayList<>();for (String name : names) {if (name.startsWith("张") && name.length() == 3){list.add(name);}}System.out.println(list);//使用Stream流解决问题List<String> list2 = names.stream().filter(s -> s.startsWith("张")).filter(a -> a.length() == 3).collect(Collectors.toList());System.out.println(list2);}
}

E:\JVsoft\Java\jdk-17\bin\java.exe -javaagent:E:\JVsoft\IntelliJIDEA2021.1.1\lib\idea_rt.jar=4519:E:\JVsoft\IntelliJIDEA2021.1.1\bin -Dfile.encoding=UTF-8 -classpath E:\JVsoft\code\out\production\collection-map-stream-app com.xinbao.d8_stream.StreamTest1
[张三丰, 张无忌, 周芷若, 赵敏, 张强]
[张三丰, 张无忌]
[张三丰, 张无忌]

1.获取Stream流

package com.xinbao.d8_stream;import java.util.*;
import java.util.stream.Stream;public class StreamTest2 {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,"张三丰", "张无忌", "周芷若", "赵敏", "张强");Stream<String> stream = names.stream();//2.如何获取Set集合的Stream流Set<String> set = new HashSet<>();Collections.addAll(set,"刘德华", "张曼玉", "张国荣", "刘嘉玲", "王祖贤");Stream<String> stream1 = set.stream();//alt + enterstream1.filter(s -> s.contains("张")).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("古力娜扎", 167.5);map.put("迪丽热巴", 164.5);map.put("马尔扎哈", 187.7);map.put("哈尼克孜", 163.8);Set<String> keys = map.keySet();Stream<String> ks = keys.stream();Collection<Double> values = map.values();Stream<Double> vs = values.stream();Set<Map.Entry<String, Double>> entries = map.entrySet();Stream<Map.Entry<String, Double>> kvs = entries.stream();kvs.filter(s -> s.getKey().contains("哈")).forEach(s -> System.out.println(s.getKey() + "-->" + s.getValue()));//4.如何获取数组的Stream流String[] names2 = {"刘德华", "张曼玉", "张国荣", "刘嘉玲", "王祖贤"};Stream<String> stream2 = Arrays.stream(names2);Stream<String> names21 = Stream.of(names2);}
}

E:\JVsoft\Java\jdk-17\bin\java.exe -javaagent:E:\JVsoft\IntelliJIDEA2021.1.1\lib\idea_rt.jar=39123:E:\JVsoft\IntelliJIDEA2021.1.1\bin -Dfile.encoding=UTF-8 -classpath E:\JVsoft\code\out\production\collection-map-stream-app com.xinbao.d8_stream.StreamTest2
张国荣
张曼玉
马尔扎哈-->187.7
哈尼克孜-->163.8

2.Stream流常见的中间方法

package com.xinbao.d6_map_impl;import java.util.Objects;public class Student implements Comparable<Student>{private String name;private int age;private double height;//this o@Override
//    public int compareTo(Student o) {
//        return this.age - o.age;//年龄升序
//    }public int compareTo(Student o) {return o.age - this.age;}public Student() {}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Student student = (Student) o;return age == student.age && Double.compare(student.height, height) == 0 && Objects.equals(name, student.name);}@Overridepublic int hashCode() {return Objects.hash(name, age, height);}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", age=" + age +", height=" + height +'}';}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;}
}

package com.xinbao.d8_stream;import com.xinbao.d6_map_impl.Student;import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.stream.Stream;public class StreamTest3 {public static void main(String[] args) {List<Double> scores = new ArrayList<>();Collections.addAll(scores,88.5,22.5,88.7,56.9,24.8,46.7,96.3);//需求1：找出成绩大于60的数据，排序输出scores.stream().filter(s -> s>60).sorted().forEach(s -> System.out.println(s));List<Student> students = new ArrayList<>();students.add(new Student("蜘蛛精", 25, 168.5));students.add(new Student("蜘蛛精", 25, 168.5));students.add(new Student("至尊宝", 23, 163.5));students.add(new Student("牛魔王", 28, 183.5));System.out.println(students);//需求2：找出年龄大于23小于30的学生，升序输出students.stream().filter(s -> s.getAge() > 23 && s.getAge() < 30).sorted((o1,o2) -> o1.getAge() - o2.getAge()).forEach(System.out::println);//需求3：取出身高最高的前三名学生，并输出System.out.println("-------------------------------------------------------------");students.stream().sorted((o1, o2) -> Double.compare(o2.getHeight(),o1.getHeight())).limit(3).forEach(System.out::println);//需求4：取出身高倒数的两名学生输出System.out.println("-------------------------------------------------------------");students.stream().sorted((o1,o2) -> Double.compare(o2.getHeight(),o1.getHeight())).skip(students.size() - 2).forEach(System.out::println);//需求5：找出身高超过168的学生名字，去重再输出System.out.println("--------------------------------------------------------------");students.stream().filter(s -> s.getHeight()>168).map(Student::getName)//.map(s->s.getName) 映射.distinct().forEach(System.out::println);//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,equals）students.stream().filter(s -> s.getHeight()>168).distinct().forEach(System.out::println);Stream<String> ls = Stream.of("李四", "王五", "刘六六");Stream<String> zs = Stream.of("张三");Stream<String> concat = Stream.concat(ls, zs);concat.forEach(System.out::println);}
}

E:\JVsoft\Java\jdk-17\bin\java.exe -javaagent:E:\JVsoft\IntelliJIDEA2021.1.1\lib\idea_rt.jar=26802:E:\JVsoft\IntelliJIDEA2021.1.1\bin -Dfile.encoding=UTF-8 -classpath E:\JVsoft\code\out\production\collection-map-stream-app com.xinbao.d8_stream.StreamTest3
88.5
88.7
96.3
[Student{name='蜘蛛精', age=25, height=168.5}, Student{name='蜘蛛精', age=25, height=168.5}, Student{name='至尊宝', age=23, height=163.5}, Student{name='牛魔王', age=28, height=183.5}]
Student{name='蜘蛛精', age=25, height=168.5}
Student{name='蜘蛛精', age=25, height=168.5}
Student{name='牛魔王', age=28, height=183.5}
-------------------------------------------------------------
Student{name='牛魔王', age=28, height=183.5}
Student{name='蜘蛛精', age=25, height=168.5}
Student{name='蜘蛛精', age=25, height=168.5}
-------------------------------------------------------------
Student{name='蜘蛛精', age=25, height=168.5}
Student{name='至尊宝', age=23, height=163.5}
--------------------------------------------------------------
蜘蛛精
牛魔王
Student{name='蜘蛛精', age=25, height=168.5}
Student{name='牛魔王', age=28, height=183.5}
李四
王五
刘六六
张三

3.Stream流常见的终结方法

package com.xinbao.d8_stream;import com.xinbao.d6_map_impl.Student;import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;public class StreamTest4 {public static void main(String[] args) {List<Student> students = new ArrayList<>();Student s1 = new Student("蜘蛛精", 25, 168.5);Student s2 = new Student("蜘蛛精", 25, 168.5);Student s3 = new Student("至尊宝", 23, 163.5);Student s4 = new Student("牛魔王", 28, 183.5);Student s5 = new Student("狐狸精", 23, 161.5);Student s6 = new Student("白骨精", 25, 161.5);Collections.addAll(students, s1, s2, s3, s4, s5, s6);//需求1：计算出高于168的人数long count = students.stream().filter(s -> s.getHeight() > 168).count();System.out.println(count);//需求2：找出最高学生对象并输出Student max = students.stream().max((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight())).get();System.out.println(max);Optional<Student> max1 = students.stream().max((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight()));System.out.println(max1);//需求3：找出最矮学生对象并输出Student min = students.stream().min((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight())).get();System.out.println(min);//需求4：找出高于165的学生对象，放到新集合中返回List<Student> collect = students.stream().filter(s -> s.getHeight() > 165).collect(Collectors.toList());System.out.println(collect);Set<Student> collect2 = students.stream().filter(s -> s.getHeight() > 165).collect(Collectors.toSet());System.out.println(collect2);//去重//流只能收集一次（类比迭代器）
//        Stream<Student> str = students.stream().filter(s -> s.getHeight() > 165);
//        List<Student> list = str.collect(Collectors.toList());
//        System.out.println(list);
//        Set<Student> set = str.collect(Collectors.toSet());//报错，流已经终结
//        System.out.println(set);//需求五：找出高于165的学生对象，并把对象的名字和身高，存入到一个Map集合返回Map<String,Double> map =students.stream().filter(s -> s.getHeight()>165)//不会自动去重，需要.distinct()去重.distinct().collect(Collectors.toMap(a -> a.getName(), a -> a.getHeight()));System.out.println(map);Object[] objects = students.stream().filter(s -> s.getHeight() > 165).toArray();System.out.println(Arrays.toString(objects));Student[] students1 = students.stream().filter(s -> s.getHeight() > 165).toArray(len -> new Student[len]);System.out.println(Arrays.toString(students1));}
}

E:\JVsoft\Java\jdk-17\bin\java.exe -javaagent:E:\JVsoft\IntelliJIDEA2021.1.1\lib\idea_rt.jar=27234:E:\JVsoft\IntelliJIDEA2021.1.1\bin -Dfile.encoding=UTF-8 -classpath E:\JVsoft\code\out\production\collection-map-stream-app com.xinbao.d8_stream.StreamTest4
3
Student{name='牛魔王', age=28, height=183.5}
Optional[Student{name='牛魔王', age=28, height=183.5}]
Student{name='狐狸精', age=23, height=161.5}
[Student{name='蜘蛛精', age=25, height=168.5}, Student{name='蜘蛛精', age=25, height=168.5}, Student{name='牛魔王', age=28, height=183.5}]
[Student{name='牛魔王', age=28, height=183.5}, Student{name='蜘蛛精', age=25, height=168.5}]
{蜘蛛精=168.5, 牛魔王=183.5}
[Student{name='蜘蛛精', age=25, height=168.5}, Student{name='蜘蛛精', age=25, height=168.5}, Student{name='牛魔王', age=28, height=183.5}]
[Student{name='蜘蛛精', age=25, height=168.5}, Student{name='蜘蛛精', age=25, height=168.5}, Student{name='牛魔王', age=28, height=183.5}]进程已结束，退出代码为 0