Java 8 stream 经典示例-白红宇

Java 8 stream 经典示例

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发布时间：2019-06-11

本文共 3224 字，大约阅读时间需要 10 分钟。

1 package org.study2.java8.stream; 2  3 import org.junit.Test; 4  5 import java.util.*; 6 import java.util.stream.Collectors; 7 import java.util.stream.Stream; 8  9 /**10  * Java 8 – Streams11  * url:http://www.studytrails.com/java/java8/java8_streams/12  * url:https://www.cnblogs.com/andywithu/p/7404101.html13  */14 public class StreamDemo {15     @Test16     public void test() {17         List
     
       genre = new ArrayList
      
       (Arrays.asList("rock", "pop", "jazz", "reggae"));18         long a = genre.stream().filter(s -> s.startsWith("r")).count();19         System.out.println(a);20 21         boolean b = genre.stream().allMatch(s -> !s.isEmpty());22         System.out.println(b);23 24         boolean b2 = genre.stream().anyMatch(s -> s.indexOf("r") == 0);25         System.out.println(b2);26 27         System.out.println(genre.stream().peek(s -> System.out.println(s)).anyMatch(s -> s.indexOf("r") == 0));28         System.out.println(genre.stream().peek(s -> System.out.println(s)).count());29 30     }31 32     //   现在有一个List
       
         的集合，如何把这个list转换成Map
        
          其中，key是user id，value是User对象33     @Test34     public void test1() {35         List
         
           users = Arrays.asList(new User(1, "Tomcat"), new User(2, "Apache"), new User(3, "Nginx"));36         Map
          
            map = users.stream().collect(Collectors.toMap(obj -> obj.getId(), obj -> obj));37 System.out.println(map);38 39 // 或者使用方法的引用40 Map
           
             map2 = users.stream().collect(Collectors.toMap(User::getId, obj -> obj));41 System.out.println(map2);42 }43 44 // 把list中的每个map中的id取出来，转换成list
            
             45 @Test46 public void test2() {47 List
             
              
               > list = new ArrayList<>();48 49 Map
               
                 map1 = new HashMap<>();50 map1.put("id", "101");51 map1.put("name", "Tomcat");52 53 Map
                
                  map2 = new HashMap<>();54 map2.put("id", "102");55 map2.put("name", "Apache");56 57 Map
                 
                   map3 = new HashMap<>();58 map3.put("id", "103");59 map3.put("name", "Nginx");60 61 list.add(map1);62 list.add(map2);63 list.add(map3);64 65 List
                  
                    ids = list.stream().map(entity -> entity.get("id")).collect(Collectors.toList());66 System.out.println(ids);67 68 // 或者69 List

User.Class

1 package org.study2.java8.stream; 2  3  4 public class User { 5  6     private int id; 7     private String name; 8  9     public User(int id, String name) {10         this.id = id;11         this.name = name;12     }13 14     public int getId() {15         return id;16     }17 18     public String toString() {19         return "User [id=" + id + ", name=" + name + "]";20     }21 22 }

详细讲解参考：

转载于:https://www.cnblogs.com/gongxr/p/10870105.html

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