Design Patterns Explained

2O4 Part IV • Putting It AM Together: Thinking in Patterns
7s there a relation-
ship between the
patterns?
Are the patterns
interrelated?
As someone new to patterns, I may not see any pattern that is obviously
dependent on another pattern, nor any pattern that sets the
context for all others.
When there is not an obvious choice, I have to work through the
combination of patterns systematically looking for the following:
• Does one pattern define how the other pattern behaves?
• Do two patterns mutually influence each other?
The Adapter pattern is about modifying the interface of a class into
another interface that the client is expecting. In this case, the interface
that needs adapting is the OOGFeature. The Bridge pattern is
about separating multiple concrete examples of an abstraction from
their implementation. In this case, the abstraction is Feature and
the implementations are the V1 and V2 systems. It sounds like the
Bridge will need the Adapter to modify OOGFeature's interface,
that is, the Bridge will use the Adapter.
Clearly there is some relationship between Bridge and Adapter.
Can I define one of the patterns without another, or is one of the
patterns needed by another?
Looking at the patterns tells us what to do.
• I can talk about the Bridge pattern as separating the Features
from the V1 and V2 systems without actually knowing how I
will use the V1 and V2 systems.
• However, I cannot talk about using an Adapter pattern to mod
ify the V2 system's interface without knowing what it will be
modified into. Without the Bridge pattern, this interface doesn't
exist. The Adapter pattern exists to modify the V2 system's
interface to the implementation interface the Bridge pattern
defines.