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

something like that (i didn't compile)

void addPerson(Person p, Map> map){
  ArrayList lst = map.get(p.name);
  if(lst == null){
     lst = new ArrayList();
  }
  lst.add(p);
  map.put(p.name, lst);
}
...
for(Person p:personsCollection>){
   addPerson(p, map);
}