Design Patterns discussion

["David Rosenstrauch" <darose AT dti.net>]

In my mind, the defining characteristic between State and Strategy is
really intent.  Superficially/structurally, yes, they look very much the
same, but they have very different intent.
Java's LayoutMangers for example would be a Strategy.  There are many
different Strategies for how you can layout Components in a Container.
I can't think of a good example of the State pattern from the JDK, but the
example given in the GOF book probably expresses the intent-based
distinction well.  GOF gives a communication state as an example, where
the behavior of the comm. link changes depending upon what state it's in.
The state pattern also dovetails with the concept of state machines, and
the State pattern follows from this by codifying each state as a concrete
object, along with a standardized abstract state API in order to refer to
them abstractly.
HTH,

DR


Chris Finlayson said:
>
> To me, a more confusing example is State versus Strategy.  I finally
> decided that if I would implement it with a set of inner class, then it
> was an example of the State pattern.  Otherwise, it was a likely
> candidate for the Strategy pattern.  By that distintion, obviously,
> only the one outer class can use the State inner-classes, while the
> Strategy pattern can be shared between different classes."
>
> --Chris.