Marking an Agent as abstract?

Question

Can Agents in AnyLogic be marked as abstract? If so, how? I'm trying to inherit certain methods from an Agent, but not others as it makes no sense for the parent Agent to have them implemented.

Answer 1

You can't declare anything abstract (class or method (AnyLogic function)) in a GUI-designed Agent, but you can create an Agent as a user-defined Java class (i.e., via New --> Java Class) which is abstract. You need to know the appropriate constructor signatures to do so, which AnyLogic doesn't document (but you can see them easily enough by viewing the generated Java code for any Agent). You'll therefore want something like the below (note the default constructor which seems never to be used):

public abstract class MyAbstractAgent extends Agent
                                implements java.io.Serializable {

    private static final long serialVersionUID = 1L;

    /**
     * Constructor in form required for an Agent subclass to be instantiated and for
     * superclass instantiation (as gleaned from looking at Java source of
     * visually-created Agents)
     */
    public MyAbstractAgent(Engine engine,
                           Agent owner,
                           AgentList<? extends MyAbstractAgent> collection) {

        super (engine, owner, collection);

    }

    /*
     * Simple constructor as now included in all AnyLogic 7 generated Agent code. Don't
     * understand when this would be invoked cf. the others so let's assert that we 
     * don't think it should
     */
    public MyAbstractAgent() {

        throw new AssertionError("Not expecting simple constructor to be used!");

    }

    // Using package visibility (the default for GUI-designed functions)
    abstract specialAbstractFunction();

}

However, since you probably want to mix in non-abstract methods, it would be preferable to have these in a GUI-designed Agent (so the class above extends MyGUI_Agent or similar), but this means having an abstract Agent which just has abstract methods (and thus one 'unnecessary' level of inheritance).

An alternative is just to 'approximate' abstract classes by forcing run-time conformance to (overridden) methods being required in any subclass Agent. Just define your required-in-subclass-Agent function in the parent as something like:

throw new IllegalStateException("Subclass must implement specialAbstractMethod()");

(or, better, throw your own MissingRequiredOverrideException or similar). Not one for the purist but then neither is the other method.