Combining design patterns
From CSSEMediaWiki
(Difference between revisions)
Line 26: | Line 26: | ||
== [[Composite]] + X == | == [[Composite]] + X == | ||
Thoughts? | Thoughts? | ||
− | |||
− |
Revision as of 00:53, 7 August 2009
Design patterns can be combined in numerous interesting ways to create super-patterns aka OO programs. A great example of this being done well is JUnit.
Contents |
Singleton + X
The singleton can be combined with a wide variety of patterns to create more specialised behaviour.
Proxy
By using a singleton on certain parts of a proxy a specific effect can be generated.
- Real Subject - Adding a singleton here means that any number of proxys can access this one class. This creates a specialised behaviour where different proxies can access a central object in different ways without being concerned that the right object is being called.
- Proxy - A singleton here makes sure that only a single proxy can be used to call any subject.
- Subject - A simple singleton here breaks the proxy pattern as no subclasses are allowed. A complex singleton, i.e. one that allows a controlled number of instances could be very powerful.
Facade
This is often a logical approach as it makes obtaining the correct object to access the complex system underneath straightforward.
Patterns Using Inheritance
- Superclass - Out of all of the subclasses there may only be one instance.
- Subclasses - Allows the inheritance hierarchy to have controlled constraints. See the attached image.
Note: the class vs object Encapsulation boundary becomes very important here.
Observer + X
Observer
- While I suppose it would be technically possible for an object to observe itself, I can't think of a pratical purpose for this.
- However, chaining observers together to add new information/functionality at each step is a possible technique.
Composite + X
Thoughts?