Re your first paragraph: nicely put! That's the separation of concerns I was referring to.
Re your second paragraph: I'd agree, except I can't detect any real convenience for the implementation. My point is that at the time it was defined, inheritance for the convenience of implementation was pretty much the norm. Our ideas about how to use objects and inheritance have evolved considerably over the past 15 years. (And the roots of this shift go back even further, which is why Java has interfaces rather than multiple inheritance.) I'll point to early window systems as one of the many "object lessons" that taught us the importance of decomposing objects. One of the earliest examples would be the original Lisp Machine window system, which suffered horrifically from a combinatorial explosion of classes resulting from this. The language provided very powerful support for multiple inheritance of implementation, but that didn't save it from the fundamental flaw of lumping separate concerns into a single object. Just to be clear -- I'm not disagreeing at all. I'm just pointing out that it was a historical mistake that we should know better than to repeat today. The bottom-line recommendation: Ignore the fact that Thread implements Runnable, and never subclass Thread. And I'll take it a step further, and suggest that the actual Runnable should seldom implement anything else, even if the thread behavior is associated with some larger object, such as a "server object". It can be an inner class that separates out the thread's behavior from the overall object. On Oct 23, 3:00 am, Kostya Vasilyev <[email protected]> wrote: > 23.10.2010 4:04, Bob Kerns пишет:> Because you're left with two dead birds > instead of one? > Having Thread implement Runnable makes using as a Runnable pretty > obvious - and wrong. The entire reason for Thread class's existence is > to be able to run code on a separate thread. That's clearly not the same > as packaging code into an object, which is what Runnable does. > > So I'd say this is a case of inheritance for convenience of > implementation, which is usually considered to be a bad. But it's worse > than that, since treating Thread as a Runnable - as permitted by its > derivation - causes Thread to completely break. -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
