Using Stream to instantiate new objects

Question

In java8, I got a Set of String:

final Set<String> nameSet = this.getNames();

And I want to get a list of People, setting the name of People based on the String from the Set. However, People class do not have a constructor like new People(name), it can only be implemented by using setName method.

In old way, I can do something like:

    List<People> peoples = new ArrayList<People>();
    for(String name: nameSet){
        People people = new People();
        people.setName(name);
        peoples.add(people);
    }

How could I use Stream to convert this?

Answer 1

If possible, it may be worth considering adding a People constructor that takes a name. Then you could do this:

List<People> peoples = nameSet.stream()
  .map(People::new)
  .collect(Collectors.toList());

If you can't add a constructor, you can either do it like this:

List<People> peoples = nameSet.stream()
  .map(name -> {
    People people = new People();
    people.setName(name);
    return people;
  }).collect(Collectors.toList());

Or better in my opinion:

List<People> peoples = nameSet.stream()
  .map(name -> createPeopleFromName(name))
  .collect(Collectors.toList());

And elsewhere in the code have this method, perhaps in a PeopleUtils class:

public static People createPeopleFromName(String name)
{
  People people = new People();
  people.setName(name);
  return people;
}

Maybe also consider renaming the class People to Person.