Java Stream操作技巧
Strean是Java8的特性,串行处理数据,更高效;parallelStream是一种高级的流处理
一. Stream创建方式
| 描述 | 示例 |
|---|---|
| Collection的stream()方法 | Arrays.asList(1,2,3).stream() |
二. 常见的流处理中间操作
1. map()
常规写法
List idcards=new ArrayList();
for(int i=0;i
idcards.add(users.get(i).getIdcard());
}
使用map()
List idcards = users.stream().map(User::getIdcard).collect(Collectors.toList())
2. filter()
Collection<Person> collection = new ArrayList();
collection.add(new Person("张三", "男"));
collection.add(new Person("李四", "女"));
collection.add(new Person("王五", "男"));
collection.add(new Person("赵六", "男"));
Stream<Person> personStream = collection.stream().filter(new Predicate<Person>() {
@Override
public boolean test(Person person) {
return "男".equals(person.getGender());//只保留男性
}
});
collection = personStream.collect(Collectors.toList());//将Stream转化为List
System.out.println(collection.toString());//查看结果
3. limit()
List<Person> personList = Arrays.asList(
new Person(1, "大毛", 30, 175),
new Person(2, "二毛", 25, 170),
new Person(3, "三毛", 25, 170),
new Person(4, "小毛", 20, 163));
// 获取 Stream 流
Stream<Person> personStream = personList.stream();
// 截取前 2 个元素
personStream.limit(2).forEach(System.out::println);
4. skip()
Stream.of(1,2,3,4,5,6,7,8).skip(5).forEach(System.out::print);
5. distinct()
List<String> list = Arrays.asList("AA", "BB", "CC", "BB", "CC", "AA", "AA");
long l = list.stream().distinct().count();
System.out.println("No. of distinct elements:"+l);
String output = list.stream().distinct().collect(Collectors.joining(","));
System.out.println(output);