> Am 10.02.2018 um 07:30 schrieb Tilman Hausherr <thaush...@t-online.de>:
> 
> Am 10.02.2018 um 07:25 schrieb Maruan Sahyoun:
>> Hi,
>> 
>>> Am 09.02.2018 um 23:06 schrieb Mark Tanner <mark.tan...@pagesuite.com>:
>>> 
>>> hey all
>>> 
>>> Java has quite strict enforcement of exception handling. I.e. if a method 
>>> can throw an exception then the calling method must handle it, and you get 
>>> plenty of compiler warnings telling you such.
>>> 
>>> We can avoid NPE's by avoiding returning null from methods completely, and 
>>> throwing an exception instead.
>> I'd think that throwing an exception if something required is missing is OK. 
>> Throwing an exception for retrieving an optional value is not. And that's 
>> the case we are talking about. And it's for the high level PD model within 
>> PDFbox - the API most of our users are using and should anyway.
>> 
>> Now for an optional value which may or may not exist - like an drop down 
>> field options - shall we return null or an empty array(collection?
> 
> Same as I said last time... I'm always wondering whether there could be a 
> case where we want to know whether the object is missing, or when we write 
> back the object and a PDF would then have an empty object instead of nothing 
> at all.

if we want to know that the object is missing we could either use the COS 
model, which I'm not proposing to change and/or use a hasXXX method to test 
upfront. 

> 
> It also depends whether the behavior is different whether an item is empty vs 
> an item is missing. Adobe behaves differently whether the color of a link 
> annotation is missing (will draw a black line) or is empty (will draw 
> nothing).

Of course we need to look at such cases and make sure that any PDFBox user can 
deal with that difference if he want's to. OTOH I'd rather draw a black border 
than throwing an NPE because I've forgootten to test that the color returned 
might be null. Again one shall be able to test if the key exists or has an 
empty value. 

Many PDFBox users do have a good knowledge of the PDF specification. So they 
understand the difference between an optional property which is not existing or 
which is existing but has no value. But users who are not fluent in the PDF 
specification will not understand that. So they might be surprised why a method 
sometimes returns null where in most of the cases it doesn't.

Maruan

> 
> Tilman
> 
> 
>> 
>> BR
>> Maruan
>> 
>> 
>>> This will also allow us to customize the message of the exception and let 
>>> the user know why they aren't getting their expected results.
>>> 
>>> Any thoughts?
>>> 
>>> Mark Tanner
>>> ________________________________________
>>> From: Tilman Hausherr [thaush...@t-online.de]
>>> Sent: 09 February 2018 18:50
>>> To: dev@pdfbox.apache.org
>>> Subject: Re: [DISCUSS] return values for functions
>>> 
>>> Am 09.02.2018 um 19:20 schrieb Andreas Lehmkuehler:
>>>> Am 17.01.2018 um 18:41 schrieb Maruan Sahyoun:
>>>>> Hi,
>>>>> 
>>>>> many of our methods return null in case an entry can not be found
>>>>> potentially causing NPEs. For 3.0 what about starting to change that
>>>>> so we return the expected object in the PDModel although I understand
>>>>> that this might mean that for some time some methods might return
>>>>> null where others might return the expected object.
>>>>> 
>>>>> E.g. in PDAnnotationTextMarkup.getQuadPoints() in the unlikely case
>>>>> that there is no sufficient entry instead of return null we could
>>>>> return an empty float[].
>>>>> 
>>>>> Wouldn't expect that we start looking for such cases but doing it as
>>>>> we touch methods.
>>>>> 
>>>>> WDYT?
>>>> I never thought about that. What exactly is the advantage of this
>>>> strategy? In the end I'm doing "is empty checks" instead of "is not
>>>> null checks".
>>>> 
>>>> Andreas
>>> It's a programming style that is expected to avoid NPEs, Sonar mentions
>>> it at some places. The advantage is that you could run a loop on the
>>> result without null checking.
>>> 
>>> Tilman
>>> 
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