Why am I getting a NullPointerException here?

Question

Long n = null;
for (Long price : new Long[]{null, 2L, 10L}) {          
n = (n != null) ? 0L : price;   
}

I'm stumped, why am I getting a NPE when I execute this code ? Seems to be just a simple assignment of n = price where price is null. Don't worry about what it means, it makes no sense.

Answer 1

In the line n = (n != null) ? 0L : price;, you have a long and a Long as the alternatives to your ?: statement. Java is going to construe this as of type long and will try to unbox the Long, instead of box the long. When price is null, as it is in the first iteration, this generates an NPE.

Answer 2

This is because price is being unboxed to match the 0L return possibility in the ternary operator.

Try instead:

Long n = null;
for (Long price : new Long[]{null, 2L, 10L}) {          
    n = (n != null) ? new Long(0L) : price;   
}

And all will run smoothly.