Extends & Implements

[mat wang <ca...@gmail.com>]

The following is just what I thought, no offense.

"extends" = "is a " relationship between subclass and superclass
   a digital clock is a clock (DigitalClock extends)
"implements" = "has a"
   a digital clock has an alarm function (DigitalClock implements Alarm)

In Camel, something made me feel uncomfortable. Such as:
public abstract  class DefaultComponent<E extends Exchange> extends
ServiceSupport implements Component<E>

Is DefaultComponent supposed to be a Component and has ServiceSupport
function (start, stop)?

Re: Extends & Implements

[James Strachan <ja...@gmail.com>]

On 8/17/07, mat wang <ca...@gmail.com> wrote:
> The following is just what I thought, no offense.

None taken :)

> "extends" = "is a " relationship between subclass and superclass
>    a digital clock is a clock (DigitalClock extends)
> "implements" = "has a"
>    a digital clock has an alarm function (DigitalClock implements Alarm)
>
> In Camel, something made me feel uncomfortable. Such as:
> public abstract  class DefaultComponent<E extends Exchange> extends
> ServiceSupport implements Component<E>
>
> Is DefaultComponent supposed to be a Component and has ServiceSupport
> function (start, stop)?

Yes. In Java you cannot have multiple inheritence; so in this case we
are inheriting the base start/stop lifecycle code from ServiceSupport,
but really a DefaultComponent is-a Component. (It just so happens it
also "is a" Service)

Currently its optional whether a Component implementation "is-a"
Service (just like lifecycle APIs/ annotations are optional in Spring
and EJB3); I guess we could make that mandatory.

-- 
James
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http://macstrac.blogspot.com/