Design Patterns discussion

[Wayne Cannon <wcannon AT sonic.net>]

Among other differences, the strategy pattern is a higher level of 
abstraction than the state pattern.  Patterns are not mutually 
exclusinve of one another, i.e., often one pattern can be used in the 
implementation of another.  For example the strategy pattern can be 
implemented using the state pattern (among other possible implementations)

The state pattern defines one particular implementation (with a couple 
of alternatives when it comes to the details) for switching between 
behaviors that differ from one state to another.  There are numerous 
other patterns that can be used to implement similar behavior changes in 
different ways, including the factory patterns, the bridge pattern, and 
the template pattern -- depending on the type of behavior, the switching 
requirements, etc.

The strategy pattern defines a way to have multiple, separately 
encapsulated algorithms that are interchangeable.  The strategy pattern 
does not define how or when to switch between interchangeable 
algorithms.  Its focus is on the encapsulation of those algorithms.  
Often, the particular strategy is selected once based on the run-time 
environment and never changed.  However, if the desired algorithm 
changes based on some state of the application, the state pattern may be 
an ideal mechanism for switching between algorithms.  On the other hand, 
the factory patterns, the bridge pattern, the template pattern, etc., 
may be more appropriate for implementing the strategy pattern, i.e., for 
switching between algorithms.

Regards,
Wayne

Thiyagarajan_BHARATHI/IN/ALCATEL@ALCATEL
 wrote:

> Please can any one explain the difference between state and strategy
> pattern, I am confused.
>
> Thanks & regards
> bharathi
>