Comparator.nullsLast does not avoid NullPointerException

Question

I want to sort a list of objects by one of nullable fields.

In order to avoid NullPointerexception I use Comparator.nullsLast. But the exception still occurs:

public class Test {      public static void main(String[] args) {         List<Bean> l = new ArrayList<>();         for (int i=0;i<5;i++) {             Bean b = new Bean("name_"+i,i);             l.add(b);         }         l.get(2).setVal(null);         System.out.println(l);         Collections.sort(l, Comparator.nullsLast(Comparator.comparing(Bean::getVal)));         System.out.println(l);     }      static class Bean{         String name;         Integer val;         // omit getters & setters & constructor     }  } 

How can I sort this kind of list?

Answer 1

You should use Comparator.nullsLast twice:

list.sort(nullsLast(comparing(Bean::getVal, nullsLast(naturalOrder())))); 

• First nullsLast will handle the cases when the Bean objects are null.
• Second nullsLast will handle the cases when the return value of Bean::getVal is null.

In case you're sure there aren't any null values in your list then you can omit the first nullsLast (as noted by @Holger) :

list.sort(comparing(Bean::getVal, nullsLast(naturalOrder())));