An object implements Faceted in order to be tightly integrated into the Facet system. An object returns a Facet of itself of a requested Type via its Faceted.getFacet(Type) method. Any lifecycle management of Facets is the responsibility of the Faceted object.

More typically -- and more powerfully -- we can create a Facet for an object that is not aware of the Facet system; we do this with the help of a FacetRegistry. Some "startup" component initializes a FacetRegistry (typically that available via class FavaBeans) with information about the Types of objects for which Facets may be created, and some FacetFactory objects to which the FacetRegistry may delegate the responsibility for actually constructing Facets. A FacetRegistry is responsible for maintaining a list of already constructed Facets for an object.

A typical interaction with a FacetRegistry starts by adding some FacetFactory objects. Given:

interface WebAccessible { /* ... */ } interface HtmlAccessible extends WebAccessible { /* ... */ } interface Vehicle { /* ... */ } Vehicle theVehicle; /* assuming already exists */ FacetFactory fac0, fac1; /* assuming these already exist */ FacetRegistry theFacets = /* ... */;

We could add:

theFacets.addFactory(new JavaType(Vehicle.class), new JavaType(WebAccessible.class), fac0); theFacets.addFactory(new JavaType(Vehicle.class), new JavaType(HtmlAccessible.class), fac1);

We could then use the FacetRegistry to obtain an HtmlAccessible Facet of the Vehicle object:

HtmlAccessible h0 = (HtmlAccessible) theFacets.getFacet(theVehicle, new JavaType(HtmlAccessible.class));

The FacetRegistry would cache this Facet so that:

theFacets.getFacet(theVehicle, new JavaType(HtmlAccessible.class)) == h0;

and would return the same Facet for compatible supertypes of that for which it was originally constructed:

theFacets.getFacet(theVehicle, new JavaType(WebAccessible.class)) == h0;

until the FacetRegistry.clearFacets(Object) method is called:

theFacets.clearFacets(theVehicle);

after which Facets for this object are created anew:

HtmlAccessible h1 = (HtmlAccessible) theFacets.getFacet(theVehicle, new JavaType(HtmlAccessible.class)); h1 != h0;

Important

We need to address lifecycle issues for Facet objects. This will apply to all things like views, etc., and will be generally useful. This is all complicated by the messy strong references in Java AWT and Swing for event listeners, which may prevent some components from getting garbage collected correctly. This will need to be addressed at some point.