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Hello everyone,

It has been a while since I last logged on. It has been a while since I really needed any major help in programming. But I am here now and I do need a bit of help.

Let me start off by saying that I have tried to do this on my own. I have been trying for over a week, and I have been banging my head against the wall hard enough that I probably have given myself a concussion or 2.

My homework assignment is to design a java simulation program that makes use of queues. It is meant to simulate a store operating, with arrivals, departures, and a closing time. It makes use of 1 server, who is either idle or busy, and 1 queue.

Requirements for the assignment is as follows:

  1. One must maintain the queue through the Java collections framework.
  2. One must have separate methods for each of the three simulation activities (arrival, departure, closing).
  3. Any customers in the queue when the doors close must be processed.
  4. One must use random numbers that are exponentially distributed for the times between arrivals of successive customers and for the service time for each customer.
  5. One must compute and output the average length of time spent in the queue per customer.
  6. One must thoroughly document the code.

I am fairly certain that I can get the three separate methods working in method form if I can get them working, or at least started, in the rest of the code. Right now, I am just trying to figure out how to make this work. I have been experiencing nothing but brain farts when I start working on this program.

The sample code provided to us:

public class asgnthr
{
	public static double expo(double mean)
	{
		double ran = Math.random();
		double ex = -mean * Math.log(ran);
		return ex;
	}
	
	public static void main(String[] args)
	{
		double meanInterArrival = 10.2;
		double meanService = 1.0;
		double clock = 0;
		double nextArrival;
		double nextDeparture;
		double closingTime = 1000;
		boolean serverIdle = true;
		boolean closed = false;
		int customerCount = 0;
		double customerWaitTime = 0;
		double totalWaitTime = 0;
		nextArrival = clock + expo(meanInterArrival);
		nextDeparture = 5000;
		while (!closed)
		{
			if (nextArrival < nextDeparture && nextArrival < closingTime)
			{	
				System.out.println("arrival");
				clock = nextArrival;
				nextArrival = clock + expo(meanInterArrival);
			}
			else if (nextDeparture < nextArrival && nextDeparture < closingTime)
				System.out.println("departure");
			else
			{
				System.out.println("closing");
				closed = true;
				closingTime = 5000;
			}
			
		
		}
	}
}

I am not asking for anyone to provide me with any code at all. Rather, I am asking for some help on where to start. How to approach this assignment. What to do in what order. What I need to add to the sample code. I have had this for over a week and I am just running head long into a wall whenever I try to think about it. With the assignment due late at night this Wednesday, I am really reaching the wire. That is why I am now asking for help.

So, any help I can get will be appreciated. It will certainly be more than I've been able to come up with on my own.

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Last Post by tkpanther
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Well, this is due in a couple of hours and this is what I managed to complete. I do not know what I need to do to solve the issues between more arrivals than departures. Any help someone can give me before 8:00PM CST tonight would be appreciated.

I have included any and all comments. I really am at a wall right now and I do not know what else to do.

import java.util.Queue;
import java.util.LinkedList;
import java.util.Iterator;

public class asgnthr
{
	public static double expo(double mean)
	{
		//The "random" method in the Math class produces random values in the range [0,1].  We make
		//our random times more realistic by transforming these into values from the exponential 
		//distribution with the appropriate mean
		//First generate a uniform random variable
		double ran = Math.random();
		//Now transform it to an expontial random variable of the indicated mean
		double ex = -mean * Math.log(ran);
		return ex;
		
	}
	
	public static void main(String[] args)
	{
		//The program will simulate a system with one queue and one server.  Customers waiting in the
		//queue will be processed on a first come, first served basis.  In order to collect waiting-time
		//statistics you will store the arrival times for each person as they enter the queue.  (Thus, the queue 
		//will contain items that store Double objects.)		
		
		//Note:  All times are given in minutes
		double meanInterArrival = 10.2;	//average time between successive arrivals
		double meanService = 1.0;		//average length of service time per customer
		double clock = 0;				//simulated clock initialized to zero before simulation starts
		
		//The only types of events that change the state of the system are the arrival of a new customer,
		//the departure of the customer currently being served, and the closing of the doors
		double nextArrival;			//the time of the next pending arrival
		double nextDeparture;			//the time of the next pending departure
		double closingTime = 5000;		//stop allowing arrivals once closing time is reached


		
		boolean serverIdle = true;		//the server is idle before the first customer arrives 
		boolean closed = false;		//the doors have not yet closed for the end of the day
		
		//Now we need some variables to collect statistical results about the simulation.  We want to know the
		//average waiting time (in the queue) per person.  So we need to count the number of people who pass through 
		//the system and accumulate the individual waiting times.
		int customerCount = 0;
		double customerWaitTime = 0;	//waiting time for the customer finishing his or her wait
		double totalWaitTime = 0;		//accumulated waiting time for all customers
		
		
		Queue<String> que=new LinkedList<String>();	//the Queue that stores the information for the arrivals
		//Schedule the time of arrival for the first customer.  Since there is no-one being served, the time of the
		//next departure is set artificially high so that it isn't chosen as the next event to happen
		nextArrival = clock + expo(meanInterArrival);
		//Since no one is being served, set the next departure time artificially high
		nextDeparture = 5000;
		
		//now the loop to run the simulation until closing time has passed and the queue has emptied out
		//NOTE:  There are many things about this loop that are incomplete.  I removed some things that we
		//haven't yet talked about in class.  There are other things that you will need to add as part of your
		//programming assignment.  I put only enough in here now to make it executable and to give you an idea
		//of the general loop structure.
		while (/*queue is not empty && */ !closed)
		{
			//find the minimum of nextArrival, nextDeparture and closingTime to determine what type of
			//event occurs next
			if (nextArrival < nextDeparture && nextArrival < closingTime)
			{	
				clock=nextArrival;
				if(serverIdle=false)
				{
					que.add(Double.toString(nextArrival));		//updates clock
				}
				else
				{
					//next event is an arrival
					System.out.println("arrival");				//indicates a new customer has arrived
					que.add(Double.toString(nextArrival));			//adds the arrival time to the queue
					nextArrival = clock + expo(meanInterArrival);	//calculates the next arrival
					nextDeparture = clock + expo(meanService);	//calculates the next departure
					customerCount =+ 1;					//increase tally of number of people served
					serverIdle=false;
				}
				
			}
			else if (nextDeparture < nextArrival && nextDeparture < closingTime)	//next event is a departure
			{	
				clock=nextDeparture;		//time is updated
				System.out.println("departure");		//denotes someone left
				if(que.isEmpty())				//if there is no one in line
				{
					serverIdle=true;	//server is no longer busy
					nextDeparture=5000;	//virtual infinity to prevent someone leaving when there is no one there.
				}
				else
				{
					customerWaitTime=nextDeparture-(Double.parseDouble(que.poll()));	//calculates how long the customer waited in line
					totalWaitTime = totalWaitTime+customerWaitTime;	//total time waiting
					meanService = totalWaitTime/customerCount;	//average time per person
					nextDeparture = clock + expo(meanService);	//next person to leave
					customerCount =+1;
				}
			}
			else
			{
				//next event is to close the doors and stop allowing arrivals
				System.out.println("closing");		//the doors have closed
				closed = true;
				closingTime = 5000;		//virtual infinity
				nextArrival = 5000;		//virtual infinity
				clock=closingTime;		//updates clock time
				if(!que.isEmpty())		//signifies there are still people waiting in line
				{
					customerWaitTime=nextDeparture-(Double.parseDouble(que.poll()));	//calculates how long the customer waited in line
					totalWaitTime = totalWaitTime+customerWaitTime;	//total time waiting
					meanService = totalWaitTime/customerCount;	//average time per person
					nextDeparture = clock + expo(meanService);	//next person to leave
					clock=nextDeparture;		//update the time
				}					
			}		
		}
	System.out.println("Average Service Time is :" + meanService);
	Iterator it=que.iterator();	//declare iterator for queue	

	}
}
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