QueueObs.java

package tutorial;
 
import java.util.*;
import umontreal.ssj.stat.*;
import umontreal.ssj.rng.*;
import umontreal.ssj.randvar.*;
 
public class QueueObs {
 
   Tally waitingTimes = new Tally("Waiting times");
   Tally averageWaits = new Tally("Average wait");
   RandomVariateGen genArr; // For interarrival times.
   RandomVariateGen genServ; // For service times.
   int cust; // Number of the current customer.
 
   public QueueObs(double lambda, double mu, int step) {
      genArr = new ExponentialGen(new MRG32k3a(), lambda);
      genServ = new ExponentialGen(new MRG32k3a(), mu);
      waitingTimes.setBroadcasting(true);
      waitingTimes.addObservationListener(new ObservationTrace(step));
      waitingTimes.addObservationListener(new LargeWaitsCollector(2.0));
   }
 
   public double simulate(int numCust) {
      waitingTimes.init();
      double Wi = 0.0;
      waitingTimes.add(Wi);
      for (cust = 2; cust <= numCust; cust++) {
         Wi += genServ.nextDouble() - genArr.nextDouble();
         if (Wi < 0.0)
            Wi = 0.0;
         waitingTimes.add(Wi);
      }
      return waitingTimes.average();
   }
 
   public void simulateRuns(int n, int numCust) {
      averageWaits.init();
      for (int i = 0; i < n; i++)
         averageWaits.add(simulate(numCust));
   }
 
   // A listener that observes each waiting time and prints every `step`th one.
   public class ObservationTrace implements ObservationListener {
      private int step;
 
      public ObservationTrace(int step) {
         this.step = step;
      }
 
      public void newObservation(StatProbe probe, double x) {
         if (cust % step == 0)
            System.out.println("Customer " + cust + " waited " + x + " time units.");
      }
   }
 
   // A listener that observes waiting times and collects those larger than
   // threshold.
   public class LargeWaitsCollector implements ObservationListener {
      double threshold;
      ArrayList<Double> largeWaits = new ArrayList<Double>();
 
      public LargeWaitsCollector(double threshold) {
         this.threshold = threshold;
      }
 
      public void newObservation(StatProbe probe, double x) {
         if (x > threshold)
            largeWaits.add(x);
      }
 
      // Maybe print the list largeWaits.
      public String formatLargeWaits() {
         return "not yet implemented...";
      }
   }
 
   public static void main(String[] args) {
      QueueObs queue = new QueueObs(1.0, 2.0, 5);
      queue.simulateRuns(2, 100);
      System.out.println("\n\n" + queue.averageWaits.report());
   }
}