SE450: Simulation: Active and Passive Objects [3/13]

Agents act.

Agents know what they want to do.

One can model agents as finite automata.

Let's say I am implementing an airline reservation system. How do I do a simulation?

A passive view of a customer:

interface Customer {
  void addFlight(Flight f);
  void removeFlight(Flight f);
}

A more active view:

public interface Agent {
  public void run();
} 
class Main {
  List<Agent> q = new List<Agent>();
  for (i=0; i<numSimulated; i++)
    q.add(new SimulatedCustomer());
  for (i=0; i<numHuman; i++)
    q.add(new HumanCustomer());
  for (currentTime=0; currentTime<endTime; currentTime+=timeStep)
    for (Agent a : q)
      a.run();
}

If we think of customers as "subscribing" to a time service:

public interface Agent {
  public void run();
} 
public interface TimeServer {
  public long currentTime();
  public void add(Agent thing);
  public void run(int duration); 
}
class Main {
  TimeService q = TimeService ();
  for (i=0; i<numSimulated; i++)
    q.add(new SimulatedCustomer());
  for (i=0; i<numHuman; i++)
    q.add(new HumanCustomer());
  q.run(duration);
}

With "sparse" time you use a priority queue:

class Main {
  TimeServer q = new TimeServer();
  for (i=0; i<numSimulated; i++)
    q.enqueue(q.currentTime, new SimulatedCustomer());
  for (i=0; i<numHuman; i++)
    q.enqueue(q.currentTime, new HumanCustomer());
  q.run(duration); 
}
public interface TimeServer {
  public long currentTime();
  public void enqueue(long time, Agent thing);
  public void run(int duration); 
}
public interface Agent {
  public void run();
} 
class SimulatedCustomer implements Agent {
  int state;
  SimulatedCustomer(TimeServer q) { ... }
  public void run() {
    switch (state) {
      case ...
        ...
        q.enqueue(q.currentTime + 500, this);
        break;
      ...
    }
  }
}
class HumanCustomer implements Agent {
  HumanCustomer(TimeServer q, UI ui) { ... }
  public void run() {
    // create a menu whose options end with:
    // q.enqueue(q.currentTime + 500, this);
    ...
    ui.displayMenu(menu);
  }
}