New structure for generator package

[pdp10]

The generator package is not currently extensible. The data structures AJObservation and AJObservationItem are difficult to maintain if new exporters requiring different or additional data will be included.

• The ArrayList in AJObservation is an important weakness. If the class AJObservation is extended, it might be tricky to deal with the array list.
• AJObservation and AJObservationItem should be replaced with a hierarchy of interfaces able to collect report information gradually. These hierarchies will define what a ReportHeader and a ReportItem are.
• Add a class Report (which won't be extended!) which represent the object mediator between importer and exporter. This class will contain a ReportHeader and a List. This class does not know the dynamic type for ReportHeader or ReportItem.
• An importer is written to parse a specific file and to store the data in specific objects (instances of ReportHeader and ReportItem). Therefore, it makes sense that the importer creates the subtypes and store the data in the mediator class Report.
• The same is true for an Exporter, which expects some data stored in certain object types and exports it in a specific format.
• As the Generator does not know the exact importer / exporter running, importers / exporters require methods to tell the world what sort of object type they return (importer), receive (exporter). These classes are the instances of ReportHeader and ReportItem. In this way, a generator can create ask the current exporter whether this is able to receive read the object types.
• Related to the previous point: an importer can parse a file containing data which could be stored in data structures subtyping its data structures, by simply discarding information; an exporter can exports data structures which are subtypes of the expected type.

[pdp10]

The last two points are not yet implemented.

[pdp10]

The focus for this issue was on re-structuring the generator package, so that the extension of importer / exporters was feasible. To do so, a generic data structure (Report.java) was implemented using String[]. This class was not extended. The importers/exporters use an enum type for inferring the column length and the importer initialises Report using this enum type. The exporter also uses the same enum type and therefore the two can communicate. To avoid downcasting, generic method are implemented in Report.java and for each exporter / importer. Although the generator is currently inferring the type of exporters, this can be removed via dependency injection, as the generator only has to pass values to setters. Extensive junit tests have been added.