Defining a Singleton Object Type in Interface Style

Defining a singleton object type is a special case of defining an object type. The difference is that a singleton object type does not require a provider. Alternatively, we might say that its unique instance is its own provider.

Because a singleton is its own provider, the SingletonTeaObject interface subsumes the other provider methods (namely, getTypeName, getTypeDescription and getConcept).

Because it is a singleton, it needs no getInstance method.

Procedure

Define a class that models the managed object type. Your class must implement the interface SingletonTeaObject. For example, when modeling a car, we could define a singleton class to represent the engine.

public class CarEngine implements SingletonTeaObject {

    public String getName() {
        // Return the name of the engine instance;
        return "Engine";
    }

    public String getDescription() {
        // Return the description of the engine instance;
        return "Car Engine";
    }

    public String getKey() {
        // Return the key that corresponds to the engine instance;
        // for example, "Engine"
    }

      // These methods give the singleton functionality 
      // that would otherwise be in the provider.

    public String getTypeName() {
        // Return the name of the engine object type.
        return "Engine";
    }

    public String getTypeDescription() {
        // Return the description of the engine object type.
        return "Car Engine";
    }

    public TeaConcept getConcept() {
        // Return the concept type of the driver.
        // In our model, it's a process that steers the car.
        return TeaConcept.RESOURCE;
    }

}

CarAgentServer server = ...
// Register other instances, including the top-level object type.
CarEngine myCarEngine = new CarEngine;
server.registerInstance(myCarEngine);
 ...
server.start();

Notice that instead of registering the provider, we register the unique instance of the engine class.