Unwanted Null Pointer Exception in ternary operator with Optional

Question

To my understanding following code should not throw Null Pointer exception as I am safely using Optional interface.

However, when I ran this code it is throwing NPE.

public class Test {
        public static void main(String[] args) {
            final Integer inte = false ? 0 : Optional.ofNullable((Integer) null).orElse(null);
         }
    }

Please let me know if I am mistaken somewhere in my code and help me to rectify the same.

Why are you casting null to an Integer? Try to write just null. — dxjuv, Dec 04 '19 at 08:44
Why are you using an Optional if you're just going to do `orElse(null)` making it null when the Optional is empty? — John Stringer, Dec 04 '19 at 08:48
This is not clear and this code will not even compile. Are you assigning it to a variable of type `Integer` or `int` ? — Michał Krzywański, Dec 04 '19 at 08:53
@JohnStringer - Question is not why I am doing that , it is why it is behaving like this ? — T-Bag, Dec 04 '19 at 08:59
@Joker then my answer is it won't throw an NPE. The code above won't compile because you've tried to call your Integer `int`, `int` being a language keyword means it doesn't work as a variable name... — John Stringer, Dec 04 '19 at 09:03
@Joker I could ask the same question to you. Do you think `int` is valid name for a variable in Java when it is a keyword that represents a primitive type? — Michał Krzywański, Dec 04 '19 at 09:04
Guys that was typo, I think u were questioning the logic compilation. — T-Bag, Dec 04 '19 at 09:12
Respect, Joker. Do you create riddles like this one on purpose? And re-post them [once a year](https://stackoverflow.com/questions/52147247/getting-unwanted-nullpointerexception-in-ternary-operator-why)? — Curiosa Globunznik, Dec 04 '19 at 09:17
Does this answer your question? [Getting unwanted NullPointerException in ternary operator - Why?](https://stackoverflow.com/questions/52147247/getting-unwanted-nullpointerexception-in-ternary-operator-why) — Curiosa Globunznik, Dec 04 '19 at 10:22

score 8 · Accepted Answer · answered Dec 04 '19 at 08:55

The reason you get a NullPointerException, is that the type of the expression false ? 0 : Optional.ofNullable((Integer) null).orElse(null) is int (by JLS Table 15.25-C).

The expression Optional.ofNullable((Integer) null).orElse(null) evaluates to null, and casting a null to an int results in a NullPointerException.

Nicktar · Answer 2 · 2019-12-04T09:41:13.770

1

Surely you'll get a NullPointerException, because your right hand side is just a very verboose way of saying null. You're wrapping a null in an Optional thus forcing the orElse which executes to null.

Having null in a statement that resolves to int, as explained by @Hoopje (even if it's assigned to an Integer variable) leads to a NullPointerException.

Just wrapping null in an Optional still gives you a null when unwrapping it again.

edited Dec 04 '19 at 09:41

answered Dec 04 '19 at 08:45

Nicktar

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The author is assigning `null` to an `Integer` reference. I hope that clears the ask. – Agam Dec 04 '19 at 08:57

T-Bag · Answer 3 · 2019-12-04T09:11:44.027

0

I found the work around

 final Integer inte = false ? (Integer)0 : Optional.<Integer>ofNullable(null).orElse(null);

or

final Integer inte = false ? (Integer)0 : Optional.ofNullable((Integer)null).orElse(null);

the type returned by the ternary operator is expected to be int (because of the literal 0).

edited Dec 04 '19 at 09:11

answered Dec 04 '19 at 08:48

T-Bag

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Actually, I did test this and it makes sense. Also, about ternary operator :"Ternary operator returns a value or expression included in the second or third part of it. It does not execute the statements." So in this case, the else part of the ternary operator was returning null, but the return type had been evaluated by the compiler to be int, instead of Integer. NPE was thrown because and int null was being returned, which is not possible. With the type casting of 0 to Integer, the returning value became Integer null, which is possible and that is what is happening. – Shivam Puri Dec 04 '19 at 08:56
3

Respect, Joker. Do you create riddles like this one on purpose? And re-post them [once a year](https://stackoverflow.com/questions/52147247/getting-unwanted-nullpointerexception-in-ternary-operator-why)? – Curiosa Globunznik Dec 04 '19 at 09:10

Unwanted Null Pointer Exception in ternary operator with Optional

3 Answers3