Descriptions shouldn't throw MetadataException

[GoogleCodeExporter]

Currently attempting to read descriptions can result in exceptions.

This is because Directory.getInt (and family) can't return nullable primitive 
values when they can't satisfy the request (because either the tag doesn't 
exist, or it has the wrong type), so throw instead.

Changing Directory.get* to return Integer instead of int (etc) will allow 
nulls, and hence we can remove throw statements from all descriptor methods, 
making the API much nicer to work with, without removing any capability.

Original issue reported on code.google.com by drewnoakes on 26 Apr 2011 at 5:28

[GoogleCodeExporter]

I dont see the advantage to return null. It still needs to be tested, so I 
would prefer to keep the exception for something that is not defined.

Original comment by andreas....@googlemail.com on 26 Apr 2011 at 9:04

[GoogleCodeExporter]

Hi Andreas,

Imagine this scenario: for a given tag the image has a string value of "FOO".

However you are expecting the type to be of int, so you call getInt.  There is 
no sensible conversion from "FOO" to an int, so it throws an exception.

There is no way you could have known that this call would fail ahead of time 
without reproducing the entire contents of the getter (it converts from many 
scenarios.)

It's uglier and more likely to be mislead, in my opinion, to catch an exception 
than to test for null.  Everything that could be known before can still be 
known now without having to catch exceptions to signal the presence of a 
certain type of value.

I have created new methods "getInteger", "getFloatObject", and 
"getDoubleObject" that return nullable numbers for times when you need them. So 
if directory.containsTag(tagType) and directory.getInteger(tagType)==null, then 
the value is there but can't be converted to an integer.

Note that arrays, strings, rationals and dates are all reference types so don't 
need any special treatment.

Descriptor.get*Description methods no longer raise MetadataException.  They are 
all capable of returning null, just like they were before.

I've also annotated the entire API with @NotNull and @Nullable, so if your IDE 
understands these tags (IntelliJ IDEA does) then you can avoid runtime NPEs.

Sorry but I did all of this before I saw your message and I must have missed 
the email notification amongst all the other notifications, otherwise I would 
have discussed this with you.  I'm pretty happy with the change though.

Take a look and let me know what you think.

Drew.

Original comment by drewnoakes on 27 Apr 2011 at 7:31

• Changed state: Fixed