Adapter Pattern: Class Adapter vs Object Adapter
I have a few questions about the Adapter pattern. I understand that the class adapter inherits from the adaptee while the object adapter has the adaptee as an object rather than inheriting from it.
When would you use a class adapter over an object adapter and vice versa? Also, what are the trade-offs of using the class adapter and the trade-offs of the object adapter?
Answer
I can see one advantage for the object adapter, depending on your programming language: if the latter does not support multiple inheritance (such as Java, for instance), and you want to adapt several adaptees in one shot, you'll be obliged to use an object adapter.
Another point for object adapter is that you can have the wrapped adaptee live his life as wanted (instantiation notably, as long as you instantiate your adapter AFTER your adaptee), without having to specify all parameters (the part for your adapter AND the part for your adaptee because of the inheritance) when you instantiate your adapter. This approach appears more flexible to me.