Difference between null==object and object==null

Question

Hi I would like to know diff between the above comparisons?

I am getting null pointer exception when I check object.getItems() == null. But if I change it to null == object.getItems(), it workes fine.

No, that change won't change if a NPE is thrown or not. Re-check your assumptions, because those two expressions are equivalent. — Joachim Sauer, Jun 09 '10 at 08:22
I get NPE both ways. What exactly is null when you try it, object? — Andrei Fierbinteanu, Jun 09 '10 at 08:25
Please post the complete Java statement, maybe the problem is just a misplaced/missing bracket. — Andreas Dolk, Jun 09 '10 at 08:27
It will be `object` that is null or a problem within getItems(). — krock, Jun 09 '10 at 08:35
@priyank.mp: Even a problem *inside* `getItems()` wouldn't make those two expressions any different. `getItems()` would be called *in both expressions*. — Joachim Sauer, Jun 09 '10 at 14:09
Could you post your object.getItems() code. I suspect there is something in that method throws NullPointerException. — Alex Khvatov, Jun 15 '10 at 17:18

score 15 · Accepted Answer · edited May 23 '17 at 12:26

15

Difference between null==object and object==null

There is no semantical difference.

object.getItems() == null and null == object.getItems() are equivalent.

Perhaps you're mixing it up with the fact that

nonNullObj.equals(obj)

and

obj.equals(nonNullObj)

can make a difference (since the second alternative could result in a NPE in case the callee is null).

edited May 23 '17 at 12:26

Community

answered Jun 09 '10 at 08:27

aioobe

what is the reason second expressoin NPE – Pedantic Jun 09 '10 at 09:32
@Rozer, if obj is null, then the .equals method call would result in an NPE. – aioobe Jun 09 '10 at 11:14

1 Answers1