Sergio Sergio - 24 days ago 7
Java Question

Class library for design patterns in Java?

I find my self writing again and again the same programming patterns in many new projects.
I have been thinking about creating my own reusable library of typical implementations of such patterns -not trying to cover all possible design patterns, but only them that experience has shown that it makes sense to put such typical implementations in a library (e.g., adapter, factory, etc ...)- but before I would like to know if there is not an existing library for this purpose already available for Java?.

I know that it is very difficult to completely generalize programming patterns in a way that they could be reused across different implementations with complex requirements (e.g., composition of patterns, classes participating in more than one pattern, etc ...). However, most of the time the pattern instantiations I need are quite simple and standard, and in many situations the implementation work could be sped up a bit with the use of such a library.

Thanks for your feedback.!

Answer

This is precisely the reason why I created PerfectJPattern. Just make sure to check out and understand the code examples. They are available for download as well as in the site documentation pages for each of the Pattern implementations. If you read the GoF book, then you will understand the examples more easily.

For instance, if you want to use the Composite Pattern in your code, and if you use PerfectJPattern you only need to specify which interface (generic parameter and class instance) you would like to use as Composite and the rest is provided to you, see PerfectJPattern Composite. At the bottom of that page, a working example is provided that shows how to accomplish that.

Another aspect you should also take into account, is that in PerfectJPattern you do not necessarily need to reuse the generic Pattern implementations (e.g. perfectjpattern-core Maven submodule), you also do have the choice to only reuse the pure abstract level (perfectjpattern-api Maven submodule) and provide the implementation yourself. In PerfectJPattern you have the flexibility of reuse at different levels of abstraction since there is a fine-grained layered design reflected also in the Maven project structure. Reusing the perfectjpattern-api gives you an abstract template guideline if you wish, that will help you speed up your own Design Pattern implementations. However, ideally you should reuse as much as possible.

Update: following up on a comment below, it is worth noting that not all Patterns can be fully compotentized see From Patterns to Components. Some Patterns can be only partially componentized and some others not at all like the case of the Singleton. The Singleton depends too much on the context and that's why you can only find an interface in PerfectJPattern. However in PerfectJPattern the following Patterns are fully componentized e.g. Observer, Command, Adapter, Decorator, Composite, Proxy, Visitor, DAO, etc.