Question

I’m currently building a Java GUI application and I’m about to implement something that seemingly requires a great deal of thinking, at least for someone as relatively inexperienced as me.

The situation

is as follows: I have a class Customer at domain level, that holds a collection of jobs, which is a class too (Job). The application is for a fictious gardening company that wants to manage its customers and the jobs it does for them.

At GUI level, I have a jList for all the customers, with a custom listmodel that extends AbstractListModel. This part of my application works perfectly, I can add/edit/remove customers easily and as it should be.

The goal

now is to implement a jTable that should show the jobs for the customer selected in the jList.

No doubt I’ll need a custom TableModel, the question is: where to get the data from? It should be noted that the collection of jobs in the Customer class is an ArrayList, and the class has no method that returns this ArrayList directly, it is only possible to get a copy, since I don’t want it to be possible to mutate the collection in the class directly from a public context.

My idea

Is to let the tablemodel have a method to change the internal collection, with a customer parameter. When the index in the jList changes, that method should be invoked, so that the jTable represents the Jobs that have been done for the customer.
When I have to edit/create/remove a job, the changes are always done on the tablemodel first, which will propagate the changes to the customer object (in case of a new job or job removal).

The question

Is that a good way to implement it? I feel it is not, because if I forget to do any changes to a Job via the tablemodel, and on the Customer or Job directly, there will be inconsistency and trouble. Are there better ways? If it involves changing other stuff, I do not mind.

(optional) Small subquestion

I lack some knowledge on the different Collections in java. I usually just go with ArrayList, like in this case in Customer for (mutable) jobs. Is there a better collection for this?

Answer 1

Not saying this is the best way to implement this, but this is how I would do it

• Make sure the customer Job list is observable. Either by using a 3th party lib which provides collections which fire events (I think Google has some available), or just make sure that every method on the Customer which updates the Job collection fires events
• The table model representing the Jobs for a certain Customer can then listen for those events and update itself accordingly
• It is unclear whether you allow to make changes to the table ui, but if you do, the table model should be responsible to propagate those changes again to the Customer

So nothing changes on your current edit/create/remove/add job code. That keeps working with your Customer and does not even know a TableModel exists. The TableModel works also directly against the Customer and does not even know there might be UI to edit/create/remove/add jobs. It just listens for any changes made to the job collection and updates itself accordingly.

It seems like a very bad idea to make the changes to the job list in all parts of your code through the table model. The Customer is your model, and the JTable is the view (MVC pattern anyone). The fact the JTable needs a different representation of your model (a TableModel) is a side-effect.