I am trying to use streams to group my objects by nationality and print them out.
But it says : "Cannot resolve method 'println"
class Person {
private String name;
private int age;
private String nationality;
public static void groupByNationality(List<Person> people) {
people
.stream()
.collect(Collectors.groupingBy(Person::getNationality))
.forEach(System.out::println);
}
CodePudding user response:
.collect(Collectors.groupingBy(Person::getNationality))
is a terminal operation that returns a Map<String,List<Person>>
.
Map
's forEach
requires a BiConsumer<? super K, ? super V> action
argument, which requires a method with two arguments. This doesn't conform with the signature of System.out::println
(all the println
methods have a single argument).
You could change
.forEach(System.out::println);
to
.forEach((key,value)->System.out.println (key ":" value));