Day21-C:\Users\Lenovo\Desktop\note\code\JavaSE\Basic\src\com\Stream-集合框架（stream）
Stream
JDK开始新增的一套API（java.util.stream），操作集合或者数组的数据
API（Application Programming Interface，应用程序编程接口）
Stream流大量结合了Lambda的语言风格来编程，提供了一种更加强大，更加简单的
package com.Stream;
import java.util.ArrayList;
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);
//[张三丰, 张无忌, 周芷若, 赵敏, 张强]
//赵找出姓张，且是三个字的名字，存入到一个新集合中去
List<String> list = new ArrayList<>();
names.forEach(s -> {
if(s.startsWith("张")&&s.length()==3){
list.add(s);
}
});
System.out.println(list);
//开始使用stream流，
List<String> list2 = names.stream().filter(s -> s.startsWith("张")).filter(a -> a.length() == 3).collect(Collectors.toList());
System.out.println(list2);
//filter(s -> s.startsWith("张")).filter(a -> a.length() == 3)可以改成filter(s -> s.startsWith("张")&&s.length() == 3)
}
}
Stream使用步骤（流水线）
数据源（集合/数组/...）----->过滤----->排序----->去重----->获取结果（alt+Enter）
package com.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();//names.stream();alt+Enter
//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","蜘蛛精","玛德","德玛西亚");
Stream<String> stream1 = set.stream();
stream1.filter(x->x.contains("德")).forEach(System.out::println);
//3.如何获取Map集合的Stream流
Map<String, Double> map = new HashMap<>();
map.put("古力娜扎",172.3);
map.put("迪丽热巴",172.3);
map.put("马尔扎哈",172.3);
map.put("卡尔扎巴",172.3);
//stream()方法是Collections提供的，Map不属于Collections方法，可以先对map集合使用keySet方法，转换为一个set类（Collections类）
//map.keySet().stream().forEach(System.out::println);只能处理键属于
Set<String> keys = map.keySet();
keys.stream().forEach(System.out::println);
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(e -> e.getKey().equals("巴")).forEach(System.out::println);
//4.如何获取的Stream流
String[] names2 = {"张翠山","东方不败","唐大山","孤独求败"};
Stream<String> s1 = Arrays.stream(names2);//Arrays.stream(names2)或者names.stream()+alt+Enter
Stream<String> s2 = Stream.of(names2);//Stream.of(names2)
}
}
package com.Stream;
import com.CollectionandMap.Student;
import java.util.ArrayList;
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,88.5,100.0,60.0,99.0,9.5,99.6,25.0);
//需求1：找出成绩大于60的数据，并升序，再输出
scores.stream().filter(s->s>=60).sorted().forEach(System.out::println);
List<Student> students = new ArrayList<>();
Student s1 = new Student("蜘蛛精",26,172.5);
Student s2 = new Student("蜘蛛精",26,172.5);
Student s3 = new Student("紫霞",23,167.6);
Student s4 = new Student("白晶晶",25,169.0);
Student s5 = new Student("牛魔王",35,183.3);
Student s6 = new Student("牛夫人",34,168.5);
Collections.addAll(students,s1,s2,s3,s4,s5,s6);
//需求2：找出年龄大于等于23，且年龄小于等于30岁的学生，并按照年龄降序输出
students.stream().filter(s ->s.getAge()>=18 &&s.getAge()<=30)
.sorted((o1, o2) -> o2.getAge()- o1.getAge())//Lambda表达式调用Comparator比较器方法
.forEach(System.out::println);
System.out.println("============================");
//需求3：取出身高最高的前三名学生，并输出
students.stream().sorted((o1, o2) -> Double.compare(o2.getHeight(),o1.getHeight()))
.limit(3).forEach(System.out::println);//limit返回长度为？的stream流（从前到后数）,取前几个数据
System.out.println("============================");
//需求4：取出身高倒数的两名学生，并输出
students.stream().sorted((o1,o2) ->Double.compare(o2.getHeight(),o1.getHeight()))
.skip(students.size()-2).forEach(System.out::println);//skip是跳过，跳过前面几个的意思
System.out.println("============================");
//需求5：找出身高超过168的学生叫什么名字，并取出重复名字再输出
students.stream().filter(s -> s.getHeight()>=168).map(Student::getName)//map映射方法，本质是将流中的 Student 对象映射为其 name 属性值
.distinct() .forEach(System.out::println);//distinct()去重复
//(Student::getName)对Student类调用它的getName方法
System.out.println("============================");
students.stream().filter(s -> s.getHeight()>=168)//这个需要重写Student类中的equals和hashCode方法
.distinct() .forEach(System.out::println);//distinct()去重复
Stream<String> st1 = Stream.of("张三","李四");
Stream<String> st2 = Stream.of("张三2","李四2","王五");
Stream<String> allSt = Stream.concat(st1, st2);
allSt.forEach(System.out::println);
}
}
package com.Stream;
import com.CollectionandMap.Student;
import java.util.*;
import java.util.stream.Collectors;
public class StreamTest4 {
public static void main(String[] args) {
List<Student> students = new ArrayList<>();
Student s1 = new Student("蜘蛛精",26,172.5);
Student s2 = new Student("蜘蛛精",26,172.5);
Student s3 = new Student("紫霞",23,167.6);
Student s4 = new Student("白晶晶",25,169.0);
Student s5 = new Student("牛魔王",35,183.3);
Student s6 = new Student("牛夫人",34,168.5);
Collections.addAll(students,s1,s2,s3,s4,s5,s6);
//需求1、请计算出身高超过168的学生有几人
long size = students.stream().filter(s -> s.getHeight() >= 168).count();
System.out.println(size);
//需求2、请找出身高最高的学生对象，并输出
//students.stream().sorted((o1, o2) -> Double.compare(o2.getHeight(),o1.getHeight())).limit(1).forEach(System.out::println);
Student s = students.stream().max((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight())).get();
System.out.println(s);
//需求3、请找出身高最矮的学生对象，并输出
Student ss = students.stream().min((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight())).get();
System.out.println(ss);
//需求4、请找出身高超过170的学生对象，并放到一个新集合中去返回
//Stream流只能收集一次，collect一次
List<Student> students1 = students.stream().filter(a -> a.getHeight() >= 170).collect(Collectors.toList());
System.out.println(students1);
Set<Student> students2 = students.stream().filter(a -> a.getHeight() >= 170).collect(Collectors.toSet());
System.out.println(students2);
//需求5请找出身高超过170的学生对象，并把学生对象的名字和身高，存入到一个Map集合中返回
Map<String, Double> map = students.stream().filter(a -> a.getHeight() >= 170)
.distinct() .collect(Collectors.toMap(a -> a.getName(), a -> a.getHeight()));
System.out.println(map);
//Object[] array = students.stream().filter(a -> a.getHeight() >= 170).toArray();//数组中的内容可以重复
Student[] array = students.stream().filter(a -> a.getHeight() >= 170).toArray(len->new Student[len]);
System.out.println(Arrays.toString(array));
}
}
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