Function.identity()
Java 8允许在接口中加入具体方法。接口中的具体方法有两种,default方法和static方法,identity()就是Function接口的一个静态方法。
Function.identity()返回一个输出跟输入一样的Lambda表达式对象,等价于形如t -> t
形式的Lambda表达式
private static void identity() { Stream<String> stream = Stream.of("I", "love", "you", "too"); Map<String, Integer> map = stream.collect(Collectors.toMap(Function.identity(), String::length)); System.out.println(map); }
输出结果为:
{love=4, too=3, I=1, you=3}
@Test public void test() { List<Person> personList = new ArrayList<>(); personList.add(new Person("hepengju", 28, 20000.0)); personList.add(new Person("lisi" , 44, 40000.0)); personList.add(new Person("wangwu" , 55, 50000.0)); personList.add(new Person("zhaoliu" , 66, 60000.0)); personList.add(new Person("zhangsan", 33, 33333.0)); personList.add(new Person("wgr", 23, 10000.0)); Map<String, Person> collect = personList.stream().collect(Collectors.toMap(Person::getName, Function.identity())); collect.forEach((name,p) ->{ System.out.println(name + ":"+p); }); }