Incidentally, boxing/unboxing actually happens at compile time ... Once you run
that code and verify if it works or not, then do the same inside of Eclipse and
see if it fails (assuming you are compiling this from eclipse not javac). If
that fails, run
javap -c Test
and you can see the decompiled code ... There should be no boxing/unboxing
calls (basically, you shouldn't see an invokevirtual except for the println),
you should just see an ifnull.
ms
On Nov 21, 2009, at 9:02 PM, Mike Schrag wrote:
> I just tested that code under JDK 1.5.0_16-b06-275 on Tiger and it works for
> me. Incidentally, my rule of thumb is "if you think it's a VM, you're wrong.
> it's your fault." This rule of thumb has never failed me.
>
> In a sample java file:
>
> public class Test {
> public static void main(String[] args) {
> Boolean a = null;
> if(a != null)
> System.out.println("s");
> else
> System.out.println("n");
> }
> }
>
> emerald:~ local$ java -fullversion
> java full version "1.5.0_16-b06-275"
> emerald:~ local$ javac Test.java
> emerald:~ local$ java Test
> n
>
> javac that and run it and see if that fails for you.
>
> ms
>
> On Nov 21, 2009, at 7:55 PM, Shravan Kumar. M wrote:
>
>> Hello Mike,
>>
>> Its the same code I have showed you (except that I changed variable names
>> for simplicity), and there is no line of code that is missing. Where "a" is
>> the EO property and when I check for it ( if(a != null) JRE throws NPE and
>> when I check for if(a == null), JRE enjoys ), its throwing exception as
>> stated. I believe this is a bug with JRE, and it seems to be fixed as per
>> David's testing in later versions of JRE.
>>
>> I think fix would be JRE shouldn't have unboxed it if its null... and they
>> seems to have realized this mistake in later versions of JRE... But its
>> wondering how a null & not null check differs in this world and they are not
>> same from JRE perspective!!! If its an error it should have thrown error
>> always...
>>
>> Thank You,
>> Shravan Kumar. M
>>
>> From: Mike Schrag <[email protected]>
>> To: Shravan Kumar. M <[email protected]>
>> Cc: WO Dev Group <[email protected]>
>> Sent: Sat, November 21, 2009 9:26:57 PM
>> Subject: Re: [OT] Weird Boolean/ Wrapper class bug
>>
>> You're not pasting the real code, I don't think. I suspect you're just
>> getting screwed by autoboxing in whatever code you're not showing. If you
>> have:
>>
>> Boolean a = null;
>> boolean b = a;
>>
>> That will result in a NPE as auto-unboxing attempts to unbox a into a
>> boolean, which throws a NPE. Somewhere in the code you didn't include is an
>> unbox into a boolean (little b) of your null Boolean.
>>
>> So, for instance:
>>
>> Boolean a = null;
>> if (a) {
>> }
>>
>> will NPE. Look more closely at the exact code, specifically the line of code
>> that actually failing, and make sure you're not getting an unbox.
>>
>> ms
>>
>> On Nov 21, 2009, at 10:23 AM, Shravan Kumar. M wrote:
>>
>>> Hello Group,
>>>
>>> Boolean a = null;
>>> if(a != null)
>>> System.out.println("s");
>>> else
>>> System.out.println("n");
>>>
>>> ----------
>>> Above code block raises NullPointerException, where as below one runs
>>> successfully!!! Same is the case with any wrapper class (Integer, Long,
>>> ...).
>>> *Its wondering what it makes difference in checking (a != null) and (a ==
>>> null)? Its just an Object check rt!*
>>>
>>> Exact exception: java.lang.NullPointerException at booleanValue()
>>> ----------
>>>
>>> Boolean a = null;
>>> if(a == null)
>>> System.out.println("s");
>>> else
>>> System.out.println("n");
>>>
>>> Thank You,
>>> Shravan Kumar. M
>>> --------------------------------
>>>
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>>
>>
>>
>
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