Description
Learning Outcomes
Implement missing methods in a queue made with a Linked List structure
Use the queue collection to track cyclical movement patterns
Consider and compare the implications of using different implementations of queues
Observe the results of a simulated snail race!
Pre-Lab
Create a new Java project called Lab6
Download the files: QueueADT.java, LinkedQueue.java, LinearNode.java,
EmptyCollectionException.java, TestQueue.java, Snail.java, and SnailRace.java
Save these downloaded files into the Lab6 src folder
Exercise 1 – Completing the Linked Queue class
1. Open LinkedQueue.java and TestQueue.java and examine the code in both classes.
2. Note that LinkedQueue is not complete; all its methods (other than the constructor) are
left empty. Without adding any additional instance variables or methods, complete the
six empty methods given the following instructions:
enqueue() – take in an element of the generic type. Create a new LinearNode
with the given input element. Make all the proper connections including special
ones if this is going to be the first element of the queue. Update count as well.
dequeue() – if the queue is empty, throw an EmptyCollectionException. If not,
retrieve the element at the front of the queue and remove it and then return it.
Remember to update the front pointer when this element is being removed and if
this is the only item then update rear as well. Decrement count to indicate this
removed item.
first() – if the queue is empty, throw an EmptyCollectionException. If not,
retrieve the element at the front of the queue and return it without removing it.
isEmpty() – return true if there are no elements, and false otherwise.
size() – return the number of elements in the queue.
toString() – if the queue is empty, return “The queue is empty.” Otherwise
return a single-line string starting with “Queue: ” and then containing all the
elements of the queue. There must be a comma and space between elements
but the last element must end with a period instead. i.e.
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LAB 6 Computer Science Fundamentals II
Queue: 1, 2, 3, 4, 5.
Hint: how can you determine whether a node is the last element?
3. Run the TestQueue file. This will test that the LinkedQueue methods were properly
implemented. If any of the test failed, fix the corresponding methods in LinkedQueue
until all the tests pass. You may add print lines in LinkedQueue to help with the
debugging. Do not add print lines in TestQueue or alter this file in any way.
Exercise 2 – Completing the Snail class
Before you begin this exercise, read this overview to explain what you’re working on. You’ll be
simulating a snail race using queues that contain the snails’ movement patterns. These queues
will need to cycle so that the pattern continues repeatedly until the race is over.
1. Open Snail.java and SnailRace.java and examine the code. Note that the methods in
Snail.java are empty. This class is used for representing each of the snails in the race.
2. Complete the constructor:
initialize the snail’s position to 0
initialize the snail’s queue “movePattern” and add each of the step sizes from the
int array to the snail’s queue in the same order they come in the array
3. Complete the move() method:
dequeue the first move pattern number and store it in a variable
re-enqueue this movement to the back of the queue so it will cycle around
increment the snail’s position by the move pattern value
don’t let the snail go past the finish line; after the movement, check its position
compared to the race length (this is a variable in the SnailRace class so examine
how the variable was made to determine how you can access it from here) and
just leave it at the finish line if was going to be past the line
Questions: Consider the possibility of using an Array Queue or a Circular Array Queue instead
of the Linked Queue being used in this simulation. Would the simulation’s results be impacted
by switching to a different Queue implementation? Which of these classes/methods would you
have to modify if you were going to use one of the other queue implementations?
4. Complete the getPosition() method to simply return (get) the position
5. Complete the display() method:
create two int variables called “dashesBefore” and “dashesAfter” and assign
them the values that represent the distance before and after the snail, i.e. when
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LAB 6 Computer Science Fundamentals II
the snail is at the start, dashesBefore is 0 and dashesAfter is 50. If the snail
moves up 1 space, dashesBefore is 1 and dashesAfter is 49, etc.
use the dashesBefore value to help in displaying that number of dashes on a
single line (use System.out.print() rather than .println() to avoid new lines)
display the snail’s shell using the icon variable (@)
use the dashesAfter value to display the dashes to the right of the snail icon (all
on one line still)
finally print out a newline character so the next snail’s path will be on a different
line than this one
6. When you have completed the Snail.java methods, go into SnailRace.java and run it.
Watch the live race in the console (you may need to resize the console to clearly watch
the race unfold)
7. Experiment with different movement patterns for the snails and you can even add more
snails to the race. This is all done in the SnailRace constructor.
Screenshot of a simulated snail race about halfway through the race:
Submission
When you have completed the lab, navigate to the weekly module page on OWL and click the
Lab link (where you found this document). Make sure you are in the page for the correct lab.
Upload the files listed below and remember to hit Save and Submit. Check that your submission
went through and look for an automatic OWL email to verify that it was submitted successfully.
Rules
Please only submit the files specified below. Do not attach other files even if they were
part of the lab.
Do not ZIP or use any other form of compressed file for your files. Attach them
individually.
Submit the lab on time. Late submissions will receive a penalty.
Forgetting to hit “Submit” is not a valid excuse for submitting late.
Submitting the files in an incorrect submission page will receive a penalty.
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LAB 6 Computer Science Fundamentals II
You may re-submit code if your previous submission was not complete or correct,
however, re-submissions after the regular lab deadline will receive a penalty.
Files to submit
LinkedQueue.java
Snail.java
SnailRace.java
