Ternary Operator and unexpected NullPointerException

Question

I am getting NullPointerException from the below line sometimes.

System.out.println("Date::"+ row != null ? row.getLegMaturityDate() : "null");

After adding brackets, it is fine.

System.out.println("Date::"+ (row != null ? row.getLegMaturityDate() : "null"));

Please clarify me the behavior. Thanks in advance.

This is why I try to limit nesting statements/expressions as much as possible. If you would split the statement into two, you wouldn't have that problem. — helpermethod, Nov 17 '11 at 13:53

score 13 · Accepted Answer · answered Nov 17 '11 at 13:49

13

"Date::" + row is never null, although row sometimes is.

That is, "Date::"+ row != null is equivalent to ("Date::"+ row) != null which is always true.

answered Nov 17 '11 at 13:49

To add to this, you should take a look at http://stackoverflow.com/questions/2137690/java-operator-precedence-guidelines – Mike Samuel Nov 17 '11 at 13:52
Thanks Christoffer. got it. @Mike, thanks for the link, informative. – Vaandu Nov 17 '11 at 13:56

score 2 · Answer 2 · edited May 23 '17 at 12:29

2

It's a matter of operator precedence. Christoffer Hammarström has the executive summary. See this page http://bmanolov.free.fr/javaoperators.php for more detail.

edited May 23 '17 at 12:29

Community

answered Nov 17 '11 at 13:53

sblundy

2 Answers2