QueueEv.java

package tutorial;
 
import umontreal.ssj.simevents.*;
import umontreal.ssj.rng.*;
import umontreal.ssj.randvar.*;
import umontreal.ssj.stat.*;
import java.util.LinkedList;
 
public class QueueEv {
 
   RandomVariateGen genArr, genServ;
   LinkedList<Customer> waitList = new LinkedList<Customer>();
   LinkedList<Customer> servList = new LinkedList<Customer>();
   Tally custWaits = new Tally("Waiting times");
   Accumulate totWait = new Accumulate("Size of queue");
 
   class Customer {
      double arrivTime, servTime;
   }
 
   public QueueEv(double lambda, double mu) {
      genArr = new ExponentialGen(new MRG32k3a(), lambda);
      genServ = new ExponentialGen(new MRG32k3a(), mu);
   }
 
   public void simulate(double timeHorizon) {
      Sim.init();
      waitList.clear();
      servList.clear();
      custWaits.init();
      totWait.init();
      new EndOfSim().schedule(timeHorizon);
      new Arrival().schedule(genArr.nextDouble());
      Sim.start();
   }
 
   class Arrival extends Event {
      public void actions() {
         new Arrival().schedule(genArr.nextDouble()); // Next arrival.
         Customer cust = new Customer(); // Cust just arrived.
         cust.arrivTime = Sim.time();
         cust.servTime = genServ.nextDouble();
         if (servList.size() > 0) { // Must join the queue.
            waitList.addLast(cust);
            totWait.update(waitList.size());
         } else { // Starts service.
            custWaits.add(0.0);
            servList.addLast(cust);
            new Departure().schedule(cust.servTime);
         }
      }
   }
 
   class Departure extends Event {
      public void actions() {
         servList.removeFirst();
         if (waitList.size() > 0) {
            // Starts service for next one in queue.
            Customer cust = waitList.removeFirst();
            totWait.update(waitList.size());
            custWaits.add(Sim.time() - cust.arrivTime);
            servList.addLast(cust);
            new Departure().schedule(cust.servTime);
         }
      }
   }
 
   class EndOfSim extends Event {
      public void actions() {
         Sim.stop();
      }
   }
 
   public static void main(String[] args) {
      double lambda = 1.0 / 10.0; // Arrival rate
      double mu = 1.0 / 9.0; // Service rate
      double T = 1000.0; // Time horizon
      QueueEv queue = new QueueEv(lambda, mu);
      queue.simulate(T);
      System.out.println(queue.custWaits.report());
      System.out.println(queue.totWait.report());
   }
}