Description
For this assignment you’ll be working with linked list classes from the data structure library lib280.
lib280 is a library of data structures that we will build up over the duration of the course. We will
start with a version that has very few data structures in it and add more with each assignment. Each
assignment will come with a new version of lib280 which contains the correct implementations of ADTs
that were the subject of the previous assignment.
Obtaining and Setting Up lib280
For this assignment the first thing you’ll need to do is to obtain a copy of lib280-asn1. It is provided along
with this assignment description on the class webpage. Download the lib280-asn1.zip file and expand its
contents somewhere in your filesystem.
The class website provides a self-guided tutorial that explains how to import lib280 into an IntelliJ
project once you have downloaded it; it is located under the “Laboratory/Tutorial Resources” heading.
First complete part 1 of the tutorial to create an empty IntelliJ project. Then complete part 2 of the tutorial
to import lib280-asn1 into your project. For question 1 complete part 3 of the tutorial to create a module
for your program that can use the classes from lib280-asn1. For questions 2 and 3 you don’t need to
complete part 3 again because you’ll just be working within the lib280-asn1 module.
Navigating lib280-asn1 Within IntelliJ
The lib280-asn1 module contains several packages. The classes of interest to use for this assignment
are in the lib280.list package. Find the lib280-asn1 module in your “project” tab, normally located
on the left side of the IntelliJ window. Expand it by clicking the little triangle beside it. This should
reveal a folder called “src”. Expand that as well. Now you will see a list of java packages that contain the
various classes in the lib280-asn1 library. For this assignment, the classes we are interested in are in the
lib280.list package, so click the triangle to expand it. You should now see classes like ArrayedList280
and LinkedList280.
Singly- and Doubly- Linked List Classes in lib280
The UML diagram below shows the class hierarchy you’ll be working with in this assignment. It may
look a bit daunting at first, but you’ll soon see it’s not that complicated. In essence, there are four pairs of
classes/interfaces (surrounded by light blue boxes1
). and in each pair, there is one class for a singly-linked
list and one for a doubly-linked list. The class/interface of each pair that pertains to doubly linked lists
extends the class/interface related to singly linked lists.
List classes
Iterator/cursor interfaces Iterator classes
List node classes
*
*
BilinkedList280
LinkedList280
«interface»
BilinearIterator280
«interface»
LinearIterator280 LinkedIterator280
BilinkedIterator280
LinkedNode280
BilinkedNode280
LinkedNode280: The node class used for a singly-linked list.
BilinkedNode280: An extension of LinkedNode280 that adds the “previous node” reference required for nodes in a doubly linked list.
LinearIterator280: An interface that defines the methods that must be supported by cursors and
iterators that can step forwards over a linear structure, such as goFirst(), goForth(), after(), etc.
BilinearIterator280: An interface that extends LinearIterator280 by adding methods that allow stepping backwards, such as goBack() and goLast().
LinkedIterator: An implementation of LinearIterator280 which is an iterator object for a singlylinked list. It is used by the LinkedList280 class to provide iterators.
BiinkedIterator: An implementation of BilinearIterator280, and an extension of LinkedIterator280,
which is an iterator object for a doubly-linked list. It is used by the BilinkedList280 class to
provide iterators.
LinkedList280: A singly-linked list class. It provides a cursor by implementing the LinearIterator280 interface. The Nodes of the list are LinkedNode280 objects, and it can provide iterators
of of type LinkedIterator.
1The light blue boxes in the UML diagram are only to show the pairs of classes that serve the same roles for singly-/doubly-linked
lists and do not represent any actual grouping within lib280. All of the pictured classes are in the same package within lib280.
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BiLinkedList280: A doubly-linked list class. It provides a cursor that can move both forwards
and backwards by implementing the BilinearIterator280 interface. The nodes of the list are
BilinkedNode280 objects, and it can provide iterators of of type BilinkedIterator.
Take a moment to familiarize yourself with these classes and their methods, particularly the LinkedList280
and LinkedIterator280 classes as you will be working on coding extensions of these classes.
Iterators
This section describes a bit more about how iterators work. Iterators provide the same functionality as a
container ADT that has a cursor, but they are separate objects from the container. This allows us to record
a cursor position that is different and independent from the position recorded by the container’s internal
cursor.
The list objects, LinkedList280 and BilinkedList280 both have methods called iterator.
The iterator method in the LinkedList280 class returns a new cursor position encapsulated in an
instance of the LinkedIterator280 class. This instance will have references directly to the nodes of
the LinkedList280 instance that created it. In essence, the LinkedIterator280 contains its own
copies of the position and prevPosition fields that appear in LinkedList280 – i.e. another cursor
that is external to the list! This cursor can be manipulated in exactly the same was as the internal cursor
of the list. If you compare the methods in LinkedIterator280 to the methods of the same name in
LinkedList280, you’ll see that they are almost identical.
Thus, each time we want a new cursor that is independent of the list’s internal cursor, we can call the
iterator method and get a new one. This adds additional flexibility. If we can get away with just using
the lists internal cursor for our purposes, then we can do so, but we have the option to create more cursors
in the form of iterators should we so desire.
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3 Your Tasks
Question 1 (8 points):
Tractor Jack is a notorious pirate captain who sails the Saskatchewan River plundering farms for
wheat, barley, and all the other grains. You may remember him from his exploits in CMPT 111. At
the end of each day, Jack enters into his computer a log of each sack of grain he has plundered, what
kind of grain it is, and how much it weighs. You will help Jack write a program to organize this data,
and calculate much of each type of grain he plundered.2
Enumerations
In this question we’re going to use a data type in Java called an enumeration. Enumerations define a
fixed set of named constant values. The grains Jack most commonly plunders are wheat, barley, oats
and rye so he wants to count the amount of those four grains separately. Any other types of grain he
wants to count together. We can us an enumeration to define five constants to denote what type of
grain is in a sack:
enum Grain {
WHEAT , BARLEY , OATS , RYE , OTHER
}
This declaration defines a data type called Grain and five values which we can assign to variables of
type Grain. You can find it at the top of Sack.java. Now we can then write in Java:
Grain g = Grain . WHEAT ; // Assign value WHEAT to the variable g
Here are some other thing we can do with enumerations that you will need:
• Enumeration types have a static method called values() which returns an array of the values it
defines. For example:
// This returns the array : { WHEAT , BARLEY , OATS , RYE , OTHER }
Grain . values ()
• Each value defined by the enumeration is associated with an integer value called an ordinal
between 0 and N − 1 (where N is the number of values in the enumeration). These ordinals are
a convenient way to map values in an enumeration to offsets of an N-element array.
Grain g = Grain . OATS ;
g . ordinal (); // returns the integer 2 ,
// because OATS is the 3rd value in the enum .
g = Grain . WHEAT ;
g . ordinal (); // returns the integer 0 ,
// because WHEAT is the 1st value in the enum .
myArray [ g . ordinal ()] // Use a value from the Grain enumeration to
// select a corresponding element of an array .
• You can find out how many values are in an enumeration asking for the length of the array
returned by the values() method:
Grain . values (). length // this is 5 because there are five values
// in the Grain enumeration .
2This question was inspired by this song (click to link). Arrrr!
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• Because enumerations have toString() methods, we can print enumerated types, and concatenate them with strings. For example:
Grain g = Grain . RYE ;
System . out . println ( g ) // prints : RYE
System . out . println ( ” The ␣ grain ␣ is : ␣ ” + g ) // prints : The grain is RYE
The Problem
Your task is to write a program to sort the sacks of grain that Jack plundered by the type of grain in
each sack, and calculate how much of each type of grain he has. This will be done by adding all the
sacks of grain containing one kind of grain to its own list.
Create a new project that references lib280-asn1 as described in the self-guided tutorial on the class
website. Add to it a class called A1Q1. Add the generatePlunder method (given below) to this class.
Add the provided Sack.java to your project (just copy it into the same folder as A1Q1.java).
Add a main() method to your A1Q1 class. Inside it, write a program that does the following:
1. Add the line import java.util.Random to the top of your A1Q1 class.
2. Call the following function to generate some data that represents Captain Jack’s plunder for the
day:
public static Sack [] generatePlunder ( int howMany ) {
Random generator = new Random ();
Sack grain [] = new Sack [ howMany ];
for (int i =0; i < howMany ; i ++) {
grain [ i ] = new Sack (
Grain . values ()[ generator . nextInt ( Grain . values (). length )] ,
generator . nextDouble () * 100 );
}
return grain ;
}
This will return a randomly generated array of Sack objects with length howMany. Sack is a simple
class that stores the type of grain in a sack (as the enumerated type Grain), and how much it
weighs. The Sack class is provided for you to use. You’ll that see its quite straightforward.
3. Create an array of linked lists of Sack objects; there should be one list for each type of grain,
including OTHER. This should be an array of LinkedList280 objects. Each list in the array
will store Sack objects for one and only one type of grain. All of the sacks containing OTHER grain
should go on the same list. Remember to create not only the array, but also instantiate a list for
each element of the array.
4. Put each Sack object in the array you created in step 1 onto one of the lists you created in step 2.
Use the ordinal of the grain type of the sack object to index the array of linked lists to find the
correct list for the type of grain, and add the sack object to that list.
5. Go through the items each list using its cursor and compute the total weight of each type of grain
that Jack plundered. Remember that since the data is randomly generated, it is possible for a list
to be empty!
6. Print a report of Jack’s plundering to the console. Below is a sample of what that should look
like.3
3
Jack seems to have a very precise scale for weighing his sacks of grain!
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Jack plundered 0.0 pounds of WHEAT
Jack plundered 75.8422984943735 pounds of BARLEY
Jack plundered 74.01721574496484 pounds of OATS
Jack plundered 48.82389493369351 pounds of RYE
Jack plundered 44.962951754620065 pounds of OTHER
Implementation Hints
Make use of the examples with enumerations provided above. They are there because you should be
using these features of enumerations in your solution! You can’t use the examples as is, but everything
they show you how to do should be used in your solution.
Question 2 (15 points):
The BilinkedList280 and BilinkedIterator280 classes in lib280-asn1 are incomplete. There
are missing method bodies in each class. Each missing method body is tagged with a // TODO comment. The javadoc headers for each method explain what each method is supposed to do4
. Many of
the methods you must implement override methods of the LinkedList280 superclass. Add your
code right into the existing files within the lib280-asn1 module.
Marks for this question are earned by implementing the methods correctly.
You are not permitted to modify any existing code in the .java files given. You may only fill in the
missing method bodies.
Question 3 (10 points):
Write a regression tests for the BilinkedList280 class. You only need to test the methods that you
had to write. You may generate test cases using white-box, black-box, or a combination of both methods. Again, write this code in the existing BiLinkedList280.java within the lib280-asn1 project. A
function header for the regression test (main() function) has already been provided.
Marks for this question will be earned for generating and coding good tests, not whether or not the
methods being tested actually work. This means that you can still get full marks on this question even
if the methods you were supposed to code in Question 2 don’t work.
4 Files Provided
lib280-asn1: A copy of lib280.
Sack.java: A copy of Captain Jack’s Sack class.
5 What to Hand In
A1Q1.java: Your program for question 1. (You do not need to submit Sack.java).
A1Q1output.txt: The output from the program you wrote for question 1 cut and paste from the IntelliJ
console.
BilinkedList280.java: Your completed doubly linked list class from question 2 and its regression test
that you wrote for question 3.
BilinkedIterator280.java: Your completed iterator class from question 2.
4The javadoc comments in these files are also good examples of how we will expect you to document methods that you write
yourself in future assignments.
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