Question

I have two variables:

final Long a;
if(...) {
     a = ...;
} else
     a = null;
String b  = "A";
....

and then later, assignment to another Long is throwing a NullPointerException:

final Long c = b.equals("B")? a*1000: a;

I am expecting c to be null if a is null, and I’m expecting b, which I know to not be B in these circumstances to prevent it being dereferenced.

So why does it throw the NullPointerException?

UPDATE: mystery solved, its auto-unboxing in the tenary operator. See https://stackoverflow.com/a/13627200/15721

Answer 1

Aha, from finding code that works I can infer what is happening:

Long a = ....; 
Long b = ... a != null? a*1000: a;

Because a*1000 is unboxing a, the tenary expression is long not Long.

Long a = ....; 
Long b = ... a != null? new Long(a*1000): a;

Keeps the tenary outcome Long and works as expected.