On the impl of AnnotatedType

[Jonathan Gibbons]

On the impl of AnnotatedType

First, note that there are 3 types called AnnotatedType, so we need to 
be careful to distinguish them.

1. javax.lang.model.type.AnnotatedType
This is a public JCP-controlled interface in the javax.lang.model package.

2. com.sun.javadoc.AnnotatedType
This is a public interface, part of the Doclet API.

3. com.sun.tools.javac.code.Type.AnnotatedType
This is an internal impl class only.


So, the jx.l.m class exists because we do not want to add extra methods 
to the supertype interface, jx.l.m.TypeMirror.    Likewise, 
c.s.j.AnnotatedType exists because we don't want to add methods to 
c.s.j.Type.

But, these reasons do not apply to c.s.t.j.code.Type, and we can add 
methods to that as we choose. So that leads us to the impl choice we now 
have: whether to use a delegation model or anon-subtype model to impl 
the jx.l.m.t.AT.

Within javac, we are not so constrained to avoid code.Type either, and 
it would be nice, as far as possible, to add virtual methods on 
code.Type to avoid unnecessary instanceof and cast tests within the 
javac code.

As for delegation vs anon-subtyping, the more we can hide that choice 
behind methods on Type, the less it matters.  I am concerned, in the 
webrevs I've done so far, at the number of anon-subtypes required, such 
that this is not a slam-dunk choice.  But the delegation approach 
requires a fair-amount of undelegating to the underlying type as well.

-- Jon