Group by field name in Java

Question

I\'m trying to group Java objects by their field, i.e Person.java

public class Person {
    String name;
    String surname;
    ....
}

Answer 1

There's probably a library that can do this more simply, but it's not too hard to do it manually:

List allPeople; // your list of all people
Map> map = new HashMap>();
for (Person person : allPeople) {
   String key = person.getName();
   if (map.get(key) == null) {
      map.put(key, new ArrayList());
   }
   map.get(key).add(person);
}

List davids = map.get("David");