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- 首页 >> Java编程 HOMEWORK 4 - Spring 2021
HOMEWORK 4 - due Tuesday, March 30th no later than 7:00PM
Reminders:
Be sure your code follows the coding style for CSE214.
Make sure you read the warnings about academic dishonesty. Remember, all work you submit for
homework or exams MUST be your own work.
Login to your grading account and click "Submit Assignment" to upload and submit your assignment.
You are allowed to use any Java API Data Structure classes such as LinkedList, ArrayList or Vector to
implement this assignment.
You may use Scanner, InputStreamReader, or any other class that you wish for keyboard input.
Assignment
Simulations can be useful to test how random processes are affected by different initial conditions. For example,
simulating the arrival of vehicles at a busy intersection can help to determine the optimal timing mechanism controlling
how long the stoplight should remain green for a particular road. In this scenario, a simulation can proceed step by step -
each step representing a specific unit of time. During each time step, vehicles may arrive in any of the lanes of the
intersection with a fixed a probability, and vehicles may pass through the intersection if the light is green in their direction.
By changing the arrival probability and stoplight timing, expected average waiting times for vehicles passing through the
intersection can be generated and compared for optimization.
In this assignment, you will be required to write a Java program to simulate vehicles passing through a busy intersection.
The intersection between Route 216 and 320 Road is currently serviced by an old fashioned timer based stop light that
frequently causes traffic jams. CSE Associates, Inc. has hired you to create a simulation of how their new Stop Light
(model # 214) would be able to better serve this intersection. Your simulation must keep track of the vehicles that arrive
at the intersection, and show the state of the vehicles queued up at the light, and describe what happens in every time
step.
Simulation Procedure
The primary simulation procedure should be contained within a static function called simulate() inside the
IntersectionSimulator class. This method should begin by initializing the intersection based on a few parameters
(listed below), and enter a loop which executes the time steps.
Your program will simulate the arrival of vehicles on up to four roads of an intersection for a specified simulation time.
You may assume that each road has two traveling directions (forward and backward), with each traveling direction
having three lanes (a left turn lane, a middle lane, and a right turn lane), for a total of 2 roads * 2 directions per road
* 3 lanes per direction = 12 lanes. The simulation will take five parameters at the onset:
1. simulationTime (int): Indicates the desired total simulation time.
2. arrivalProbability (double): Indicates the probability that a vehicle will arrive at any lane during a time
step.
3. numRoads (int): Indicates the number of two-way roads that meet at this intersection.
4. names (String[]): An array of size numRoads indicating the name of each road.
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5. greenTimes (int[]): An array of size numRoads indicating the green time for each road.
Note: The two array parameters (names and greenTimes) should be equal in size and have corresponding indices (i.e.
names[i] corresponds to a road having a green time of geenTimes[i]).
Initialization
Before the first time step, your program should create a new array of TwoWayRoads equal in size to the array parameters.
A new TwoWayRoad object should be created at each index of this new array, initializing each new road with the name and
greenTime at the corresponding index of the array parameters (names and greenTimes, respectively). Once this array has
been created and initialized, it should be used to construct an Intersection instance, which will be used to keep track of
the light during simulation and allow vehicles to pass through the intersection. Lastly, a BooleanSource object should be
created (initializing it's probability member variable to arrivalProbability) which will be used to determine if vehicles
have arrived during simulation.
During execution, the 'light' will be simulated using the lightIndex member variable of the Intersection instance. This
variable indicates the index of the road in the roads array which currently has the active light (the current active light may
be in the GREEN state or LEFT_TURN state, as described by the LightValue enum below). When the Intersection instance
is constructed, it initializes the lightIndex member variable to 0 and the countdownTimer to the greenTime member
variable of roads[lightIndex]. After each time step, the timer is decremented by 1. Once the timer reaches 0, the
lightIndex is incremented, returning back to 0 if it equals the size of the roads array (i.e. modular arithmetic), and the
countdownTimer is again set to roads[lightIndex]. This process repeats continually until the simulation ends.
Time Steps
On each time step, the program should determine if a vehicle has arrived for each lane in the intersection (all 12). This
can be accomplished by calling the occurs() method on the BooleanSource object for each lane. If a vehicle has arrived
(i.e. occurs() returns true), the program should create a new Vehicle object, initialize it's timeArrived member variable
to the current time step value, and enqueue the vehicle onto the appropriate lane.
After all lanes have been considered for arrival, roads[lightIndex] should pass vehicles through the intersection - one
vehicle per lane, but only if the lane is allowed to proceed (see the LightValue enum below for more detail on the light
rules). When a vehicle is dequeued from a lane, the program should add the vehicle's wait time to the total wait time for
the simulation, and increment the number of cars passed through the intersection. The vehicle's wait time can be
calculated by subtracting it's arrivalTime from the current time step value. If all lanes are empty after having been
dequeued (or ignored if they were empty), then the program should preempt the countdown timer and switch the light to
the next road.
Note: On any particular time step, a maximum of 6 vehicles may be queued onto lanes of the intersection, and a
maximum of 4 vehicles may pass through an intersection (if the lightValue is GREEN, then the right and middle lanes
can proceed in both directions, but the left lanes cannot). In other words, any lane can be enqueued and dequeued only
once on a given time step. A case you should consider is if a lane of the road with the green light is empty at the
beginning of the time step, and has an arrival during the time step. If this happens, then the vehicle will be enqueued and
dequeued from the lane during the same time step, resulting in a wait time of zero (this is the equivalent of driving
through a green light without having to wait).
After these operations have been completed, the simulation should output the current state of the intersection to the
user. This should include the number of cars on each of the 12 lanes of the intersection, as well as their current wait
times. In addition, the current total wait time, total number of cars, and average wait time should be shown in tabular
form (please see the sample I/O for examples). The program now proceeds to the next time step, repeating the process
until the time step value is equal to simulationTime.
Finalization
Once the time step counter reaches simulationTime, no more vehicles should arrive at the intersection. The simulation
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should proceed as normal until all lanes have been cleared and the intersection is empty. Once the intersection is clear
of vehicles, the simulation should end and the program should display the results to the user. The output parameters
should include the total wait time by all vehicles, the total number of vehicles passing through the intersection, and the
average wait time for vehicles during the simulation.
The entire procedure is summarized by the following Activity Diagram:
Activity Diagram
Required Classes
The following outlines the required classes you must implement for this assignment. You may write additional classes if
you feel they will help you implement this assignment, as well as private helper methods. However, each of the classes
and methods below must be included if you are to receive full credit. Also note that you should not include any method
which exposes references to private member variables or allows a user to interact with the class in an undefined way (if
you are unsure, please contact a TA or the instructor). The following UML Diagram outlines the class relationship
structure:
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UML Diagram
1. BooleanSource class
Write a fully-documented class called BooleanSource which abstracts a random occurrence generator. This class should
be constructed with an initial arrival probability (0.0 < probability ≤ 1.0) which represents the likelihood that a Vehicle
will arrive at any particular lane at the beginning of each time step. This method should also contain a single method,
occurs() which returns true if a vehicle arrives and false it does not.
private double probability
public BooleanSource(double initProbability)
Brief:
Constructor which initializes the probability to the indicated parameter.
Parameters:
initProbability
Probability used to construct this BooleanSource object. The probability should be greater than 0 and
less than or equal to 1.
Preconditions:
0 < initProbability ≤ 1.
Throws:
IllegalArgumentException
If initProbability ≤ 0 or initProbability > 1.
public boolean occurs()
Brief:
Method which returns true with the probability indicated by the member variable probability.
Preconditions:
probability is a valid probability (0 < probability ≤ 1).
Returns:
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Boolean value indicating whether an event has occurred or not.
Note:
This method should utilize Math.random() to generate the random occurrence.
2. LightValue enum
Write a simple Enum named LightValue, which lists the phases a particular stoplight lane may be in. These states should
include GREEN, RED, and LEFT_SIGNAL (we are considering yellow to be part of green). Each TwoWayRoad instance (defined
below) will have its own LightValue, which should correspond to the following rules:
1. GREEN indicates that the right and middle lanes may proceed, but the left lane cannot (for both directions).
2. RED indicates that no lane may proceed (for both directions).
3. LEFT_SIGNAL indicates that left can proceed, but the right and middle lanes cannot (for both directions).
Cars in a particular lane may proceed (dequeue one car per time interval) when it is their turn to go, according to the
rules above. If you still need help with Java Enum types, you can read about them in this Java tutorial.
3. Vehicle Class
Write a fully documented class named Vehicle. This class represents a car which passes through the intersection. Each
instance must contain the serialId (the first car to arrive at the intersection is serialId 1, the second car to arrive is
serialId 2, the n'th car to arrive will have serialId >n) and the time it arrived (stored as an int). The car must be
initialized with a serialId and the time it arrived. The serial counter is static and stores the number of vehicles that have
arrived at the intersection so far. It is the only variable that is modifiable.
The Vehicle class itself is actually immutable. This means once it has been constructed, no data within the instance can
be changed (the static serialCounter can and should be incremented on each constructor call). From the UML diagram,
note that the public constructor takes all the member variables as arguments. Data can still be read via the getter
methods.
private static int serialCounter = 0
private int serialId
private int timeArrived
public Vehicle(int initTimeArrived)
Brief:
Default Constructor. You should automatically increment the serialCounter, and set the serialId to its new
value.
Parameters:
initTimeArrived
Time the vehicle arrived at the intersection.
Preconditions:
initTimeArrived > 0.
Throws:
IllegalArgumentException
If initTimeArrived ≤ 0.
4. VehicleQueue class
Lanes in our simulator will be modelled as a Queue of Vehicles. You may implement a Queue of vehicles however you
like, and are encouraged to use any Java API class you prefer. Remember that the VehicleQueue class must implement
the following methods in order to comply with the Queue ADT:
void enqueue(Vehicle v)
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Vehicle dequeue()
int size()
boolean isEmpty()
Note: If you decide to use a Java API class to implement VehicleQueue, you must use inheritance (extend a Java API
class) to simplify the class definition.
5. TwoWayRoad Class
Write a fully documented class called TwoWayRoad that represents one of the roads in our intersection. Each road it bidirectional,
with each direction having three lanes - a left turn lane, a middle lane, and a right turn lane. Lanes, modelled
by VehicleQueues, hold the vehicles before they pass through the intersection. These lanes will be stored in a two
dimensional array - the first index indicates the direction of travel on the road, and the second index indicates the lane on
the road. In order to access a specific direction, you should use the constants FORWARD_WAY and BACKWARD_WAY to access
the directions of the road. In order to access specific lanes in a particular direction, you should use the second dimension
of the array, accessed by the consants LEFT_LANE, MIDDLE_LANE, RIGHT_LANE. Your TwoWayRoad class must be able to
check whether any of the lanes in the road have Vehicle objects in them by using the boolean isEmpty(int wayIndex,
int laneIndex) method. It should also be able to add Vehicle objects to the lanes using the void enqueueVehicle(int
wayIndex, int laneIndex, Vehicle vehicle) method. Furthermore, you should allow vehicles to pass through the
intersection, adding the Vehicles that have been dequeued to an array to returned to the caller.
Brief:
public final int FORWARD_WAY = 0;
public final int BACKWARD_WAY = 1;
public final int NUM_WAYS = 2;
public final int LEFT_LANE = 0;
public final int MIDDLE_LANE = 1;
public final int RIGHT_LANE = 2;
public final int NUM_LANES = 3;
private String name
private int greenTime
The maximum total number of steps this road can be active (this number is inclusive of the
leftSignalGreenTime).
private int leftSignalGreenTime
The number of steps this road remains in the LEFT_SIGNAL state.
Should be initialized to 1.0/NUM_LANES * greenTime in the constructor.
private VehicleQueue lanes[NUM_WAYS][NUM_LANES]
private LightValue lightValue
public TwoWayRoad(String initName, int initGreenTime)
Brief:
Default Constructor. You should automatically initialize the array and all of its member objects, as well as
initializing leftSignalGreenTime to 1.0/NUM_LANES * initGreenTime.
Parameters:
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initName
The name of the road.
initGreenTime
The amount of time that the light will be active for this particular road. This is the total of the time the
light should display green for cars going forward/turning right, as well as for cars going left.
Preconditions:
initGreenTime > 0.
Postconditions:
This road is initialized with all lanes initialized to empty queues, and all instance variables initialized.
Throws:
IllegalArgumentException
If initGreenTime ≤ 0 or initName=null.
public Vehicle[] proceed(int timerVal)
Brief:
Executes the passage of time in the simulation. The timerVal represents the current value of a countdown
timer counting down total green time steps. The light should be in state GREEN any time the timerval is
greater than leftSignalGreenTime. When timerVal is less than or equal to leftSignalGreenTime, the light
should change to LEFT_SIGNAL. After the execution of timerVal == 1, or if there are no vehicles left the light
should change state to RED.
Parameters:
timerVal
The current timer value, determines the state of the light.
Preconditions:
The TwoWayRoad object should be instantiated.
Returns:
An array of Vehicles that has been dequeued during this time step.
Postconditions:
Any Vehicles that should have been dequeued during this time step should be dequeued and placed in
the return array.
Throws:
IllegalArgumentException
If timerval ≤ 0.
public void enqueueVehicle(int wayIndex, int laneIndex, Vehicle vehicle)
Brief:
Enqueues a vehicle into a the specified lane.
Parameters:
wayIndex
The direction the car is going in.
laneIndex
The lane the car arrives in.
vehicle
The vehicle to enqueue; must not be null.
Preconditions:
The TwoWayRoad object should be instantiated.
Postconditions:
Given that the vehicle specified was not null, and the position given was not invalid (and no exception
was thrown), the vehicle should be added to the end of the proper queue.
Throws:
IllegalArgumentException
If wayIndex > 1 || wayIndex < 0 || laneIndex < 0 || laneIndex > 2 or vehicle==null
.
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public boolean isLaneEmpty(int wayIndex, int laneIndex)
Brief:
Checks if a specified lane is empty.
Parameters:
wayIndex
The direction of the lane.
laneIndex
The index of the lane to check.
Preconditions:
The TwoWayRoad object should be instantiated.
Returns:
true if the lane is empty, else false.
Postconditions:
The TwoWayRoad object should remain unchanged
Throws:
IllegalArgumentException
If wayIndex > 1 || wayIndex < 0 || laneIndex < 0 || laneIndex > 2.
6. Intersection class
Write a fully documented class named Intersection. This class represents a crossing of two or more roads at a stop
light in our simulation. The class consists of an array of TwoWayRoad objects representing the crossing roads, as well as a
countdown timer and a light index. Intersection must contain the following private member variables: roads
(TwoWayRoad[]), lightIndex (int), and countdownTimer (int). The Intersection class must also feature the following
public methods: void timeStep(), and void enqueueVehicle(int roadIndex, int wayIndex, int laneIndex), as well
as a display() method which prints the intersection to the terminal.
private TwoWayRoad[] roads
Array of roads which cross at this intersection.
private int lightIndex
Indicates the road in roads with the active light (either green or left turn signal).
private int countdownTimer
Tracks the remaining time steps available for the road currently indicated by lightIndex.
public Intersection(TwoWayRoads[] initRoads)
Brief:
Constructor which initializes the roads array.
Parameters:
initRoads
Array of roads to be used by this intersection.
Preconditions:
initRoads is not null.
Length of initRoadsis less than or equal to MAX_ROADS.
All indices of initRoads are not null.
Postconditions:
This object has been initialized to a Intersection object managing the roads array.
Throws:
IllegalArgumentException
If initRoads is null.
If any index of initRoads is null.
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initRoads.length > MAX_ROADS.
public Vehicle[] timeStep()
Brief:
Performs a single iteration through the intersection. This method should apply all the logic defined in this
specification related to the passing of cars through the intersection and switching the selected road (Note:
LightValue changes for a particular road should be handled within the TwoWayRoad class itself and not
within this method). Please refer to the Simulation Procedure section above for instructions on how to
apply this procedure.
Postconditions:
The intersection has dequeued all lanes with a green light (if non-empty) and returned an array containing
the Vehicles.
Returns:
An array of Vehicles which have passed though the intersection during this time step.
public void enqueueVehicle(int roadIndex, int wayIndex, int laneIndex, Vehicle
vehicle)
Brief:
Enqueues a vehicle onto a lane in the intersection.
Parameters:
roadIndex
Index of the road in roads which contains the lane to enqueue onto.
wayIndex
Index of the direction the vehicle is headed. Can either be TwoWayRoad.FORWARD or
TwoWayRoad.BACKWARD
laneIndex
Index of the lane on which the vehicle is to be enqueue. Can either be TwoWayRoad.RIGHT_LANE,
TwoWayRoad.MIDDLE_LANE, or TwoWayRoad.LEFT_LANE.
vehicle
The Vehicle to enqueue onto the lane.
Preconditions:
0 ≤ roadIndex < roads.length.
0 ≤ wayIndex < TwoWayRoad.NUM_WAYS.
0 ≤ laneIndex < TwoWayRoad.NUM_LANES.
vehicle != null.
Throws:
IllegalArgumentException
If vehicle is null.
If any of the index parameters above are not within the valid range..
public void display()
Brief:
Prints the intersection to the terminal in a neatly formatted manner. See the sample I/O for an example of
what this method should display.
Note:
The sample I/O shown below requires you to print some of the VehicleQueues in reverse. Think about how
you might be able to do this using a stack (e.g. java.util.Stack).
7. IntersectionSimulator class
Write a fully documented class named IntersectionSimulator. This class represents the manager of the simulation -- it
does the heavy lifting, per se. The main function's responsibility is to get the parameters for the simulation and pass
them to the simulate() method, either by interactive prompt or command line (See below).
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public static void main(String args[])
Start for application, asks user for following values: simulationTime (int), arrivalProbability (double),
numRoads (int), a name for each road, and a "green" time for each road. This method also parses command
line for these args. If args.length < 5, the above is read in at execution time. Otherwise, refer to the end of
this document on how to parse the command line arguments.
public static void simulate(int simulationTime, double arrivalProbability, String[]
roadNames, int[] maxGreenTimes):
This method does the actual simulation. Above, a Activity Diagram is presented to demonstrate how the
simulation works. This method actually implements the algorithm described by that diagram, using
Intersection, BooleanSource, and TwoWayRoad.
Note: The simulationTime is how long cars can 'appear'. The actual simulation can last longer -- long enough
for every car to pass the intersection.
Warning: You should make sure that you catch ALL exceptions that you throw anywhere in your code. Exceptions are
used to indicate illegal or unsupported operations so that your program can handle unexpected events gracefully and
prevent a crash. Your program should NOT crash from any of the above exceptions (it should not crash from any
exception, but especially not one that you throw yourself).
Input Format:
The simulator should be run either by prompting the user for input at the beginning of the program or by parsing the
command line arguments passed to the program. You may assume that the arguments will be passed in in the proper
order and of the correct data type.
Command Line Arguments
Command line arguments are text values passed into a program at run time. For example, to compile your java files, you
could run javac *.java in a terminal. In this homework assignment, you will be able to start your program with the
following options in order:
simulationTime
arrivalProbability
numRoads
[numRoads long list of names (Strings)]
[numRoads long list of maxGreenTimes (ints)]
Example execution command line:
java IntersectionSimulator 5 0.25 3 Road1 Road2 Road3 3 4 5
To make it easier for you to include command line arguments in your code, here is some sample code for parsing
required arguments:
if (args.length > 1) {
int simTime = Integer.parseInt(args[0]);
double prob = Double.parseDouble(args[1]);
int numRoads = Integer.parseInt(args[2]);
String[] names = new String[numRoads];
String[] times = new int[numRoads];
for (int i = 0; i < numRoads; ++i) {
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names[i] = args[3 + i];
times[i] = Integer.parseInt(args[3 + numRoads + i]);
}
// process args in simTime, prob, numRoads, names, times.
}
// Else: interactive
To test in Eclipse, go to Menu Bar > Project > Properties > Run/Debug settings > Edit the listed run configuration (usually
the name of your project) > Arguments tab.
Output Format:
All lists must be printed in a nice and tabular form as shown in the sample output. You may use C style formatting as
shown in the following example. The example below shows two different ways of displaying the name and address at
pre-specified positions 21, 26, 19, and 6 spaces wide. If the ‘-’ flag is given, then it will be left-justified (padding will be on
the right), else the region is right-justified. The ‘s’ identifier is for strings, the ‘d’ identifier is for integers. Giving the
additional ‘0’ flag pads an integer with additional zeroes in front.
String name = "Doe Jane";
String address = "32 Bayview Dr.";
String city = "Fishers Island, NY";
int zip = 6390;
System.out.println(String.format("%-21s%-26s%19s%06d", name, address, city, zip));
System.out.printf("%-21s%-26s%19s%06d", name, address, city, zip);
// Output
Doe Jane 32 Bayview Dr. Fishers Island, NY 06390
Doe Jane 32 Bayview Dr. Fishers Island, NY 06390
Sample Input/Output:
// Comment in green, input in red, output in black
Sample I/O:
Welcome to IntersectionSimulator 2021
Input the simulation time: 6
Input the arrival probability: 0.2 // chance of car entering a lane, for all lanes.
Input number of Streets: 2
Input Street 1 name: Route 216 // must be unique names & not the empty string
Input Street 2 name: Route 216 // on duplicate detected, re-prompt for name
Duplicate Detected.
Input Street 2 name: 320 Road
Input max green time for Route 216: 4
Input max green time for 320 Road: 3
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Starting Simulation...
################################################################################
Time Step: 1
Green Light for Route 216. // Select first road at start.
Timer = 4 // Initialize timer to max green time for road.
ARRIVING CARS:
Car[001] entered Route 216, going FORWARD in LEFT lane.
Car[002] entered Route 216, going BACKWARD in MIDDLE lane.
Car[003] entered 320 Road, going FORWARD in RIGHT lane.
PASSING CARS:
// Car[001] can't pass since 216-FORWARD-LEFT has red light (x).
Car[002] passes through. Wait time of 0.
// Car[003] can't pass since 320-FORWARD-RIGHT has red light (x).
Route 216:
FORWARD BACKWARD
============================== ===============================
[001] [L] x [R]
------------------------------ -------------------------------
[M] [M] // [002] passed through.
------------------------------ -------------------------------
[R] x [L]
============================== ===============================
320 Road:
FORWARD BACKWARD
============================== ===============================
[L] x x [R]
------------------------------ -------------------------------
[M] x x [M]
------------------------------ -------------------------------
[003] [R] x x [L]
============================== ===============================
STATISTICS:
Cars currently waiting: 2 cars
Total cars passed: 1 cars
Total wait time: 0 turns
Average wait time: 0.00 turns
################################################################################
Time Step: 2
Green Light for Route 216.
Timer = 3 // Timer decrements
ARRIVING CARS:
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Car[004] entered Route 216, going FORWARD in MIDDLE lane.
Car[005] entered Route 216, going FORWARD in RIGHT lane.
Car[006] entered Route 216, going BACKWARD in RIGHT lane.
Car[007] entered 320 Road, going FORWARD in LEFT lane.
Car[008] entered 320 Road, going BACKWARD in MIDDLE lane.
PASSING CARS:
Car[004] passes through. Wait time of 0.
Car[005] passes through. Wait time of 0.
Car[006] passes through. Wait time of 0.
Route 216:
FORWARD BACKWARD
============================== ===============================
[001] [L] x [R] // [006] passed through.
------------------------------ -------------------------------
[004] passed through. // [M] [M]
------------------------------ -------------------------------
[005] passed through. // [R] x [L]
============================== ===============================
320 Road:
FORWARD BACKWARD
============================== ===============================
[007] [L] x x [R]
------------------------------ -------------------------------
[M] x x [M] [008]
------------------------------ -------------------------------
[003] [R] x x [L]
============================== ===============================
STATISTICS:
Cars currently waiting: 4 cars
Total cars passed: 4 cars
Total wait time: 0 turns
Average wait time: 0.00 turns
################################################################################
Time Step: 3
Green Light for Route 216.
Timer = 2
ARRIVING CARS:
Car[009] entered Route 216, going FORWARD in RIGHT lane.
Car[010] entered Route 216, going BACKWARD in LEFT lane.
Car[011] entered 320 Road, going FORWARD in MIDDLE lane.
Car[012] entered 320 Road, going BACKWARD in RIGHT lane.
PASSING CARS:
Car[009] passes through. Wait time of 0.
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Route 216:
FORWARD BACKWARD
============================== ===============================
[001] [L] x [R]
------------------------------ -------------------------------
[M] [M]
-
HOMEWORK 4 - due Tuesday, March 30th no later than 7:00PM
Reminders:
Be sure your code follows the coding style for CSE214.
Make sure you read the warnings about academic dishonesty. Remember, all work you submit for
homework or exams MUST be your own work.
Login to your grading account and click "Submit Assignment" to upload and submit your assignment.
You are allowed to use any Java API Data Structure classes such as LinkedList, ArrayList or Vector to
implement this assignment.
You may use Scanner, InputStreamReader, or any other class that you wish for keyboard input.
Assignment
Simulations can be useful to test how random processes are affected by different initial conditions. For example,
simulating the arrival of vehicles at a busy intersection can help to determine the optimal timing mechanism controlling
how long the stoplight should remain green for a particular road. In this scenario, a simulation can proceed step by step -
each step representing a specific unit of time. During each time step, vehicles may arrive in any of the lanes of the
intersection with a fixed a probability, and vehicles may pass through the intersection if the light is green in their direction.
By changing the arrival probability and stoplight timing, expected average waiting times for vehicles passing through the
intersection can be generated and compared for optimization.
In this assignment, you will be required to write a Java program to simulate vehicles passing through a busy intersection.
The intersection between Route 216 and 320 Road is currently serviced by an old fashioned timer based stop light that
frequently causes traffic jams. CSE Associates, Inc. has hired you to create a simulation of how their new Stop Light
(model # 214) would be able to better serve this intersection. Your simulation must keep track of the vehicles that arrive
at the intersection, and show the state of the vehicles queued up at the light, and describe what happens in every time
step.
Simulation Procedure
The primary simulation procedure should be contained within a static function called simulate() inside the
IntersectionSimulator class. This method should begin by initializing the intersection based on a few parameters
(listed below), and enter a loop which executes the time steps.
Your program will simulate the arrival of vehicles on up to four roads of an intersection for a specified simulation time.
You may assume that each road has two traveling directions (forward and backward), with each traveling direction
having three lanes (a left turn lane, a middle lane, and a right turn lane), for a total of 2 roads * 2 directions per road
* 3 lanes per direction = 12 lanes. The simulation will take five parameters at the onset:
1. simulationTime (int): Indicates the desired total simulation time.
2. arrivalProbability (double): Indicates the probability that a vehicle will arrive at any lane during a time
step.
3. numRoads (int): Indicates the number of two-way roads that meet at this intersection.
4. names (String[]): An array of size numRoads indicating the name of each road.
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5. greenTimes (int[]): An array of size numRoads indicating the green time for each road.
Note: The two array parameters (names and greenTimes) should be equal in size and have corresponding indices (i.e.
names[i] corresponds to a road having a green time of geenTimes[i]).
Initialization
Before the first time step, your program should create a new array of TwoWayRoads equal in size to the array parameters.
A new TwoWayRoad object should be created at each index of this new array, initializing each new road with the name and
greenTime at the corresponding index of the array parameters (names and greenTimes, respectively). Once this array has
been created and initialized, it should be used to construct an Intersection instance, which will be used to keep track of
the light during simulation and allow vehicles to pass through the intersection. Lastly, a BooleanSource object should be
created (initializing it's probability member variable to arrivalProbability) which will be used to determine if vehicles
have arrived during simulation.
During execution, the 'light' will be simulated using the lightIndex member variable of the Intersection instance. This
variable indicates the index of the road in the roads array which currently has the active light (the current active light may
be in the GREEN state or LEFT_TURN state, as described by the LightValue enum below). When the Intersection instance
is constructed, it initializes the lightIndex member variable to 0 and the countdownTimer to the greenTime member
variable of roads[lightIndex]. After each time step, the timer is decremented by 1. Once the timer reaches 0, the
lightIndex is incremented, returning back to 0 if it equals the size of the roads array (i.e. modular arithmetic), and the
countdownTimer is again set to roads[lightIndex]. This process repeats continually until the simulation ends.
Time Steps
On each time step, the program should determine if a vehicle has arrived for each lane in the intersection (all 12). This
can be accomplished by calling the occurs() method on the BooleanSource object for each lane. If a vehicle has arrived
(i.e. occurs() returns true), the program should create a new Vehicle object, initialize it's timeArrived member variable
to the current time step value, and enqueue the vehicle onto the appropriate lane.
After all lanes have been considered for arrival, roads[lightIndex] should pass vehicles through the intersection - one
vehicle per lane, but only if the lane is allowed to proceed (see the LightValue enum below for more detail on the light
rules). When a vehicle is dequeued from a lane, the program should add the vehicle's wait time to the total wait time for
the simulation, and increment the number of cars passed through the intersection. The vehicle's wait time can be
calculated by subtracting it's arrivalTime from the current time step value. If all lanes are empty after having been
dequeued (or ignored if they were empty), then the program should preempt the countdown timer and switch the light to
the next road.
Note: On any particular time step, a maximum of 6 vehicles may be queued onto lanes of the intersection, and a
maximum of 4 vehicles may pass through an intersection (if the lightValue is GREEN, then the right and middle lanes
can proceed in both directions, but the left lanes cannot). In other words, any lane can be enqueued and dequeued only
once on a given time step. A case you should consider is if a lane of the road with the green light is empty at the
beginning of the time step, and has an arrival during the time step. If this happens, then the vehicle will be enqueued and
dequeued from the lane during the same time step, resulting in a wait time of zero (this is the equivalent of driving
through a green light without having to wait).
After these operations have been completed, the simulation should output the current state of the intersection to the
user. This should include the number of cars on each of the 12 lanes of the intersection, as well as their current wait
times. In addition, the current total wait time, total number of cars, and average wait time should be shown in tabular
form (please see the sample I/O for examples). The program now proceeds to the next time step, repeating the process
until the time step value is equal to simulationTime.
Finalization
Once the time step counter reaches simulationTime, no more vehicles should arrive at the intersection. The simulation
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should proceed as normal until all lanes have been cleared and the intersection is empty. Once the intersection is clear
of vehicles, the simulation should end and the program should display the results to the user. The output parameters
should include the total wait time by all vehicles, the total number of vehicles passing through the intersection, and the
average wait time for vehicles during the simulation.
The entire procedure is summarized by the following Activity Diagram:
Activity Diagram
Required Classes
The following outlines the required classes you must implement for this assignment. You may write additional classes if
you feel they will help you implement this assignment, as well as private helper methods. However, each of the classes
and methods below must be included if you are to receive full credit. Also note that you should not include any method
which exposes references to private member variables or allows a user to interact with the class in an undefined way (if
you are unsure, please contact a TA or the instructor). The following UML Diagram outlines the class relationship
structure:
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UML Diagram
1. BooleanSource class
Write a fully-documented class called BooleanSource which abstracts a random occurrence generator. This class should
be constructed with an initial arrival probability (0.0 < probability ≤ 1.0) which represents the likelihood that a Vehicle
will arrive at any particular lane at the beginning of each time step. This method should also contain a single method,
occurs() which returns true if a vehicle arrives and false it does not.
private double probability
public BooleanSource(double initProbability)
Brief:
Constructor which initializes the probability to the indicated parameter.
Parameters:
initProbability
Probability used to construct this BooleanSource object. The probability should be greater than 0 and
less than or equal to 1.
Preconditions:
0 < initProbability ≤ 1.
Throws:
IllegalArgumentException
If initProbability ≤ 0 or initProbability > 1.
public boolean occurs()
Brief:
Method which returns true with the probability indicated by the member variable probability.
Preconditions:
probability is a valid probability (0 < probability ≤ 1).
Returns:
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Boolean value indicating whether an event has occurred or not.
Note:
This method should utilize Math.random() to generate the random occurrence.
2. LightValue enum
Write a simple Enum named LightValue, which lists the phases a particular stoplight lane may be in. These states should
include GREEN, RED, and LEFT_SIGNAL (we are considering yellow to be part of green). Each TwoWayRoad instance (defined
below) will have its own LightValue, which should correspond to the following rules:
1. GREEN indicates that the right and middle lanes may proceed, but the left lane cannot (for both directions).
2. RED indicates that no lane may proceed (for both directions).
3. LEFT_SIGNAL indicates that left can proceed, but the right and middle lanes cannot (for both directions).
Cars in a particular lane may proceed (dequeue one car per time interval) when it is their turn to go, according to the
rules above. If you still need help with Java Enum types, you can read about them in this Java tutorial.
3. Vehicle Class
Write a fully documented class named Vehicle. This class represents a car which passes through the intersection. Each
instance must contain the serialId (the first car to arrive at the intersection is serialId 1, the second car to arrive is
serialId 2, the n'th car to arrive will have serialId >n) and the time it arrived (stored as an int). The car must be
initialized with a serialId and the time it arrived. The serial counter is static and stores the number of vehicles that have
arrived at the intersection so far. It is the only variable that is modifiable.
The Vehicle class itself is actually immutable. This means once it has been constructed, no data within the instance can
be changed (the static serialCounter can and should be incremented on each constructor call). From the UML diagram,
note that the public constructor takes all the member variables as arguments. Data can still be read via the getter
methods.
private static int serialCounter = 0
private int serialId
private int timeArrived
public Vehicle(int initTimeArrived)
Brief:
Default Constructor. You should automatically increment the serialCounter, and set the serialId to its new
value.
Parameters:
initTimeArrived
Time the vehicle arrived at the intersection.
Preconditions:
initTimeArrived > 0.
Throws:
IllegalArgumentException
If initTimeArrived ≤ 0.
4. VehicleQueue class
Lanes in our simulator will be modelled as a Queue of Vehicles. You may implement a Queue of vehicles however you
like, and are encouraged to use any Java API class you prefer. Remember that the VehicleQueue class must implement
the following methods in order to comply with the Queue ADT:
void enqueue(Vehicle v)
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Vehicle dequeue()
int size()
boolean isEmpty()
Note: If you decide to use a Java API class to implement VehicleQueue, you must use inheritance (extend a Java API
class) to simplify the class definition.
5. TwoWayRoad Class
Write a fully documented class called TwoWayRoad that represents one of the roads in our intersection. Each road it bidirectional,
with each direction having three lanes - a left turn lane, a middle lane, and a right turn lane. Lanes, modelled
by VehicleQueues, hold the vehicles before they pass through the intersection. These lanes will be stored in a two
dimensional array - the first index indicates the direction of travel on the road, and the second index indicates the lane on
the road. In order to access a specific direction, you should use the constants FORWARD_WAY and BACKWARD_WAY to access
the directions of the road. In order to access specific lanes in a particular direction, you should use the second dimension
of the array, accessed by the consants LEFT_LANE, MIDDLE_LANE, RIGHT_LANE. Your TwoWayRoad class must be able to
check whether any of the lanes in the road have Vehicle objects in them by using the boolean isEmpty(int wayIndex,
int laneIndex) method. It should also be able to add Vehicle objects to the lanes using the void enqueueVehicle(int
wayIndex, int laneIndex, Vehicle vehicle) method. Furthermore, you should allow vehicles to pass through the
intersection, adding the Vehicles that have been dequeued to an array to returned to the caller.
Brief:
public final int FORWARD_WAY = 0;
public final int BACKWARD_WAY = 1;
public final int NUM_WAYS = 2;
public final int LEFT_LANE = 0;
public final int MIDDLE_LANE = 1;
public final int RIGHT_LANE = 2;
public final int NUM_LANES = 3;
private String name
private int greenTime
The maximum total number of steps this road can be active (this number is inclusive of the
leftSignalGreenTime).
private int leftSignalGreenTime
The number of steps this road remains in the LEFT_SIGNAL state.
Should be initialized to 1.0/NUM_LANES * greenTime in the constructor.
private VehicleQueue lanes[NUM_WAYS][NUM_LANES]
private LightValue lightValue
public TwoWayRoad(String initName, int initGreenTime)
Brief:
Default Constructor. You should automatically initialize the array and all of its member objects, as well as
initializing leftSignalGreenTime to 1.0/NUM_LANES * initGreenTime.
Parameters:
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initName
The name of the road.
initGreenTime
The amount of time that the light will be active for this particular road. This is the total of the time the
light should display green for cars going forward/turning right, as well as for cars going left.
Preconditions:
initGreenTime > 0.
Postconditions:
This road is initialized with all lanes initialized to empty queues, and all instance variables initialized.
Throws:
IllegalArgumentException
If initGreenTime ≤ 0 or initName=null.
public Vehicle[] proceed(int timerVal)
Brief:
Executes the passage of time in the simulation. The timerVal represents the current value of a countdown
timer counting down total green time steps. The light should be in state GREEN any time the timerval is
greater than leftSignalGreenTime. When timerVal is less than or equal to leftSignalGreenTime, the light
should change to LEFT_SIGNAL. After the execution of timerVal == 1, or if there are no vehicles left the light
should change state to RED.
Parameters:
timerVal
The current timer value, determines the state of the light.
Preconditions:
The TwoWayRoad object should be instantiated.
Returns:
An array of Vehicles that has been dequeued during this time step.
Postconditions:
Any Vehicles that should have been dequeued during this time step should be dequeued and placed in
the return array.
Throws:
IllegalArgumentException
If timerval ≤ 0.
public void enqueueVehicle(int wayIndex, int laneIndex, Vehicle vehicle)
Brief:
Enqueues a vehicle into a the specified lane.
Parameters:
wayIndex
The direction the car is going in.
laneIndex
The lane the car arrives in.
vehicle
The vehicle to enqueue; must not be null.
Preconditions:
The TwoWayRoad object should be instantiated.
Postconditions:
Given that the vehicle specified was not null, and the position given was not invalid (and no exception
was thrown), the vehicle should be added to the end of the proper queue.
Throws:
IllegalArgumentException
If wayIndex > 1 || wayIndex < 0 || laneIndex < 0 || laneIndex > 2 or vehicle==null
.
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public boolean isLaneEmpty(int wayIndex, int laneIndex)
Brief:
Checks if a specified lane is empty.
Parameters:
wayIndex
The direction of the lane.
laneIndex
The index of the lane to check.
Preconditions:
The TwoWayRoad object should be instantiated.
Returns:
true if the lane is empty, else false.
Postconditions:
The TwoWayRoad object should remain unchanged
Throws:
IllegalArgumentException
If wayIndex > 1 || wayIndex < 0 || laneIndex < 0 || laneIndex > 2.
6. Intersection class
Write a fully documented class named Intersection. This class represents a crossing of two or more roads at a stop
light in our simulation. The class consists of an array of TwoWayRoad objects representing the crossing roads, as well as a
countdown timer and a light index. Intersection must contain the following private member variables: roads
(TwoWayRoad[]), lightIndex (int), and countdownTimer (int). The Intersection class must also feature the following
public methods: void timeStep(), and void enqueueVehicle(int roadIndex, int wayIndex, int laneIndex), as well
as a display() method which prints the intersection to the terminal.
private TwoWayRoad[] roads
Array of roads which cross at this intersection.
private int lightIndex
Indicates the road in roads with the active light (either green or left turn signal).
private int countdownTimer
Tracks the remaining time steps available for the road currently indicated by lightIndex.
public Intersection(TwoWayRoads[] initRoads)
Brief:
Constructor which initializes the roads array.
Parameters:
initRoads
Array of roads to be used by this intersection.
Preconditions:
initRoads is not null.
Length of initRoadsis less than or equal to MAX_ROADS.
All indices of initRoads are not null.
Postconditions:
This object has been initialized to a Intersection object managing the roads array.
Throws:
IllegalArgumentException
If initRoads is null.
If any index of initRoads is null.
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initRoads.length > MAX_ROADS.
public Vehicle[] timeStep()
Brief:
Performs a single iteration through the intersection. This method should apply all the logic defined in this
specification related to the passing of cars through the intersection and switching the selected road (Note:
LightValue changes for a particular road should be handled within the TwoWayRoad class itself and not
within this method). Please refer to the Simulation Procedure section above for instructions on how to
apply this procedure.
Postconditions:
The intersection has dequeued all lanes with a green light (if non-empty) and returned an array containing
the Vehicles.
Returns:
An array of Vehicles which have passed though the intersection during this time step.
public void enqueueVehicle(int roadIndex, int wayIndex, int laneIndex, Vehicle
vehicle)
Brief:
Enqueues a vehicle onto a lane in the intersection.
Parameters:
roadIndex
Index of the road in roads which contains the lane to enqueue onto.
wayIndex
Index of the direction the vehicle is headed. Can either be TwoWayRoad.FORWARD or
TwoWayRoad.BACKWARD
laneIndex
Index of the lane on which the vehicle is to be enqueue. Can either be TwoWayRoad.RIGHT_LANE,
TwoWayRoad.MIDDLE_LANE, or TwoWayRoad.LEFT_LANE.
vehicle
The Vehicle to enqueue onto the lane.
Preconditions:
0 ≤ roadIndex < roads.length.
0 ≤ wayIndex < TwoWayRoad.NUM_WAYS.
0 ≤ laneIndex < TwoWayRoad.NUM_LANES.
vehicle != null.
Throws:
IllegalArgumentException
If vehicle is null.
If any of the index parameters above are not within the valid range..
public void display()
Brief:
Prints the intersection to the terminal in a neatly formatted manner. See the sample I/O for an example of
what this method should display.
Note:
The sample I/O shown below requires you to print some of the VehicleQueues in reverse. Think about how
you might be able to do this using a stack (e.g. java.util.Stack).
7. IntersectionSimulator class
Write a fully documented class named IntersectionSimulator. This class represents the manager of the simulation -- it
does the heavy lifting, per se. The main function's responsibility is to get the parameters for the simulation and pass
them to the simulate() method, either by interactive prompt or command line (See below).
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public static void main(String args[])
Start for application, asks user for following values: simulationTime (int), arrivalProbability (double),
numRoads (int), a name for each road, and a "green" time for each road. This method also parses command
line for these args. If args.length < 5, the above is read in at execution time. Otherwise, refer to the end of
this document on how to parse the command line arguments.
public static void simulate(int simulationTime, double arrivalProbability, String[]
roadNames, int[] maxGreenTimes):
This method does the actual simulation. Above, a Activity Diagram is presented to demonstrate how the
simulation works. This method actually implements the algorithm described by that diagram, using
Intersection, BooleanSource, and TwoWayRoad.
Note: The simulationTime is how long cars can 'appear'. The actual simulation can last longer -- long enough
for every car to pass the intersection.
Warning: You should make sure that you catch ALL exceptions that you throw anywhere in your code. Exceptions are
used to indicate illegal or unsupported operations so that your program can handle unexpected events gracefully and
prevent a crash. Your program should NOT crash from any of the above exceptions (it should not crash from any
exception, but especially not one that you throw yourself).
Input Format:
The simulator should be run either by prompting the user for input at the beginning of the program or by parsing the
command line arguments passed to the program. You may assume that the arguments will be passed in in the proper
order and of the correct data type.
Command Line Arguments
Command line arguments are text values passed into a program at run time. For example, to compile your java files, you
could run javac *.java in a terminal. In this homework assignment, you will be able to start your program with the
following options in order:
simulationTime
arrivalProbability
numRoads
[numRoads long list of names (Strings)]
[numRoads long list of maxGreenTimes (ints)]
Example execution command line:
java IntersectionSimulator 5 0.25 3 Road1 Road2 Road3 3 4 5
To make it easier for you to include command line arguments in your code, here is some sample code for parsing
required arguments:
if (args.length > 1) {
int simTime = Integer.parseInt(args[0]);
double prob = Double.parseDouble(args[1]);
int numRoads = Integer.parseInt(args[2]);
String[] names = new String[numRoads];
String[] times = new int[numRoads];
for (int i = 0; i < numRoads; ++i) {
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names[i] = args[3 + i];
times[i] = Integer.parseInt(args[3 + numRoads + i]);
}
// process args in simTime, prob, numRoads, names, times.
}
// Else: interactive
To test in Eclipse, go to Menu Bar > Project > Properties > Run/Debug settings > Edit the listed run configuration (usually
the name of your project) > Arguments tab.
Output Format:
All lists must be printed in a nice and tabular form as shown in the sample output. You may use C style formatting as
shown in the following example. The example below shows two different ways of displaying the name and address at
pre-specified positions 21, 26, 19, and 6 spaces wide. If the ‘-’ flag is given, then it will be left-justified (padding will be on
the right), else the region is right-justified. The ‘s’ identifier is for strings, the ‘d’ identifier is for integers. Giving the
additional ‘0’ flag pads an integer with additional zeroes in front.
String name = "Doe Jane";
String address = "32 Bayview Dr.";
String city = "Fishers Island, NY";
int zip = 6390;
System.out.println(String.format("%-21s%-26s%19s%06d", name, address, city, zip));
System.out.printf("%-21s%-26s%19s%06d", name, address, city, zip);
// Output
Doe Jane 32 Bayview Dr. Fishers Island, NY 06390
Doe Jane 32 Bayview Dr. Fishers Island, NY 06390
Sample Input/Output:
// Comment in green, input in red, output in black
Sample I/O:
Welcome to IntersectionSimulator 2021
Input the simulation time: 6
Input the arrival probability: 0.2 // chance of car entering a lane, for all lanes.
Input number of Streets: 2
Input Street 1 name: Route 216 // must be unique names & not the empty string
Input Street 2 name: Route 216 // on duplicate detected, re-prompt for name
Duplicate Detected.
Input Street 2 name: 320 Road
Input max green time for Route 216: 4
Input max green time for 320 Road: 3
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Starting Simulation...
################################################################################
Time Step: 1
Green Light for Route 216. // Select first road at start.
Timer = 4 // Initialize timer to max green time for road.
ARRIVING CARS:
Car[001] entered Route 216, going FORWARD in LEFT lane.
Car[002] entered Route 216, going BACKWARD in MIDDLE lane.
Car[003] entered 320 Road, going FORWARD in RIGHT lane.
PASSING CARS:
// Car[001] can't pass since 216-FORWARD-LEFT has red light (x).
Car[002] passes through. Wait time of 0.
// Car[003] can't pass since 320-FORWARD-RIGHT has red light (x).
Route 216:
FORWARD BACKWARD
============================== ===============================
[001] [L] x [R]
------------------------------ -------------------------------
[M] [M] // [002] passed through.
------------------------------ -------------------------------
[R] x [L]
============================== ===============================
320 Road:
FORWARD BACKWARD
============================== ===============================
[L] x x [R]
------------------------------ -------------------------------
[M] x x [M]
------------------------------ -------------------------------
[003] [R] x x [L]
============================== ===============================
STATISTICS:
Cars currently waiting: 2 cars
Total cars passed: 1 cars
Total wait time: 0 turns
Average wait time: 0.00 turns
################################################################################
Time Step: 2
Green Light for Route 216.
Timer = 3 // Timer decrements
ARRIVING CARS:
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Car[004] entered Route 216, going FORWARD in MIDDLE lane.
Car[005] entered Route 216, going FORWARD in RIGHT lane.
Car[006] entered Route 216, going BACKWARD in RIGHT lane.
Car[007] entered 320 Road, going FORWARD in LEFT lane.
Car[008] entered 320 Road, going BACKWARD in MIDDLE lane.
PASSING CARS:
Car[004] passes through. Wait time of 0.
Car[005] passes through. Wait time of 0.
Car[006] passes through. Wait time of 0.
Route 216:
FORWARD BACKWARD
============================== ===============================
[001] [L] x [R] // [006] passed through.
------------------------------ -------------------------------
[004] passed through. // [M] [M]
------------------------------ -------------------------------
[005] passed through. // [R] x [L]
============================== ===============================
320 Road:
FORWARD BACKWARD
============================== ===============================
[007] [L] x x [R]
------------------------------ -------------------------------
[M] x x [M] [008]
------------------------------ -------------------------------
[003] [R] x x [L]
============================== ===============================
STATISTICS:
Cars currently waiting: 4 cars
Total cars passed: 4 cars
Total wait time: 0 turns
Average wait time: 0.00 turns
################################################################################
Time Step: 3
Green Light for Route 216.
Timer = 2
ARRIVING CARS:
Car[009] entered Route 216, going FORWARD in RIGHT lane.
Car[010] entered Route 216, going BACKWARD in LEFT lane.
Car[011] entered 320 Road, going FORWARD in MIDDLE lane.
Car[012] entered 320 Road, going BACKWARD in RIGHT lane.
PASSING CARS:
Car[009] passes through. Wait time of 0.
3/28/21, 8:53 AM
https://blackboard.stonybrook.edu/bbcswebdav/pid-6035411-dt-con…rid-53765865_1/courses/1214-CSE-214-SEC01-51104/hw4%286%29.html Page 14 of 20
Route 216:
FORWARD BACKWARD
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[001] [L] x [R]
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[M] [M]
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