Newbie confronts GWT, GUICE, GIN, MVP and Dependency Injection.

Well the life of a fairly new Java developer is interestingly complex.  I guess that is why I love computer programming its like solving little puzzles all day long.  Studying the concepts of OO using Java has been very interesting and has given my skill set a new edge.   Originally I come from an engineering background and have learned computer programming on-the-job.  This technique has gotten me through the last ten years of investment banks, universities and blue-chip companies but it hadn’t left me with a very good design metholody when it comes to applications.   I utilised OO rudimentarily, using classes as containers for similar functionality.  In the main still running a procedural based programming paradigm where most parts of the application have to know what the other parts are doing for it to work correctly.  Highly coupled you might say….

So where am I now?  Well through a process of SCJP training, examining example code, watching Google IO sessions, and attempting to program a small GWT application.  I am a lot clearer on some aspects, but on others, well this adventure has opened up a great many doors on how to design my programs.

Two design patterns which are paramount in my opinion for good design are Dependency Injection and a MVP architecture?  Why you may ask?  In short Google uses them and that’s good enough for me.
MVP stands for Model View Presenter and is similar to MVC except in our case the view knows nothing of the presenter, so you can swap out the views for different ones, i.e. a web page or an Android application, and your application still works.  As long as your view implements its relevant presenters interface. 

As a design pattern this approach appears to be very good and the example Contacts application that Google provides helps clear up any confusion from purely reading the articles.  What is interesting with the example is that the core of the application is demonstrated very clearly, allowing other developers to easily pick it up, and event bus and rpc handling is centralised, removing the ugly spaghetti code, that I currently, but have not yet talked about.  

At the moment I have developed a very simple CRM application using GWT located at: http://sohocrm.appspot.com.  Completing this project allows me to get my feet dirty and by doing so has lead me to these design methodologies which I now have to attempt to embrace and learn.  I can feel my brain whirring as I try to understand these concepts. 

So MVP is a good pattern because it gives a very clear architecture on how your application works.  However in order to clear up more of the spaghetti code we also need to utilise dependency injection.  Now I only have a basic concept of this, so please correct me if I am wrong in what I am about to say, but DI is this.   When instantiating an object you create additional objects which are utilised in order for the object to complete its class.  This might be any object which is declared with a new keyword.  What this means is that the current class is dependent on these other classes in order for it to work.   The dependency component.   Now in order to write modular code and to make testing easier, it would be good to have any dependencies injected into the constructor as an instance when the object is created.  That way you can clearly see what classes your objects are dependent on and it allows modular testing to be a lot clearer.  I think it applies to only classes which exist within your current project as I don’t think you will be injecting in int's, textboxes etc, but the exact delimination of this area is unsure at the moment – for myself – and I hope to clear that up over the coming weeks.    Google uses a product developed by itself called GUICE to do this on the server side java and another called GIN which is a GWT version for the client side.

How did I come across these technologies?  Well after building that relatively small application I noticed how spaghetti looking my code was and realised early on that this can’t be the way much larger programs such as Google Wave are constructed so realised, intuitively knew as we all do when we are accomplishing a task we aren’t quite proficient at, that there must  be another way.

So the next stage of my application is to re-write it in a MVP style.  Then take a look at how I can implement Gin and Guice to build a scalable, understandable and modular application.