Although this project is not based on any particular tutorial, I mainly used the Refactoring Guru explanation as reference when implementing the code.

There is a base class representing a business entity (MIPOccurrence). This entity has base operations that define its basic behaviour (IOccurrence). However, we assume a dashboard needs additional operations to generate charts. Instead of adding these chart operations into the entity, we extended the entity by using the decorator pattern (ChartDecoratorMIPOccurrence).

• IOccurrence represents the set of common operations for any MIPOccurrence entity. This interface is used by all classes in this project;

• MIPOccurrence is the base class. It implements the IOccurrence operations. This represents the basic behaviour of an occurrence;

• BaseDecorator is the superclass that defines a decorator. As MIPOccurrence, it implements IOccurrence operations. Thus, both MIPOccurrence & BaseDecorator are IOccurrence. Classes that add new behaviour to MIPOccurrence must extend BaseDecorator. This class has a parameter in the constructor, used to wrap the base class (MIPOccurrence);

• ChartDecoratorMIPOccurrence represents the operations necessary for creating dashboard charts. This class extends BaseDecorator and, therefore, is also an IOccurrence. To extend MIPOccurrence behaviour, it wraps MIPOccurrence by using the constructor parameter, on the class instantiation. The ChartDecoratorMIPOccurrence method, getChartData() uses MIPOccurrence base operations, implemented from IOccurrence, to generate data for the chart.

The Figure shows the test execution. A MIPOccurrence is firstly created. Its method getOccurrences() is called to test the entity is working. Second, the ChartDecoratorMIPOccurrence class is instantiated, as it is BaseDecorator, due to the inheritance.

During the instantiation, ChartDecoratorMIPOccurrence wraps the MIPOccurrence instance. Finally, the ChartDecoratorMIPOccurrence method, getChartData(), uses the getOccurrences() method to extract data for generating the chart.

Notice that this diagram is deeper than necessary, as it shows both BaseDecorator and IOccurrence - but, it may help understand better the inheritance role.

mvn clean test