Annotations across modules

[Alex Buckley]

On 11/16/2015 3:19 AM, Philippe Marschall wrote:
> On 12.11.15 14:50, Stephen Colebourne wrote:
>> My understanding of annotations today is that annotations are not
>> required at runtime. ie. if an annotation is placed into a class at
>> compile time but the .class file for the annotation is not available
>> on the runtime classpath. then there is no error.
>>
>> Does this change in any way with modules?
>>
>> My specific case is wrt @ConstructorProperties which is in java.beans.
>> In 9, a user may run my software without the java.beans module. Can I
>> safely assume that if the annotation is available on the compile
>> module path but not the runtime module path, everything will be OK
>> (ie. no error)?
>
> My understanding is that you can't have optional dependencies. So if you
> have @ConstructorProperties in your source you also need to have a
> java.desktop module dependency in your module-info.java. If your library
> is in the module path the java.desktop module then it needs to be
> present at runtime.
>
> The only option you have is to make your jar not a modular jar by one of
> those:
>   - not providing a module-info.class
>   - not putting your module in the module path

This is all true -- a static reference to 
java.beans.ConstructorProperties necessitates a dependency on 
java.desktop at compile time.

The reason for my stripped-down answer was that Stephen phrased the 
question using some rather abstract language -- "an annotation is placed 
into a class", "a user may run my software ...". This made me think 
something clever was going on -- for example, the user's dependency on 
java.desktop is factored out and Stephen's software receives a Class 
object for java.beans.ConstructorProperties from someone else.

Alex