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

Using java-8 with the Collectors class and streams, you can do this:

Map> mapByName = 
    allPeople.stream().collect(Collectors.groupingBy(Person::getName));

List allDavids = mapByName.getOrDefault("David", Collections.emptyList());

Here I used getOrDefault so that you get an empty immutable list instead of a null reference if there is no "David" in the original list, but you can use get if you prefer to have a null value.

Hope it helps! :)