General Instructions

• Assignments must be submitted using Canvas.

• Programs must be written in Java.

• VERY IMPORTANT: Canvas is very fragile when it comes to submitting multiple files.  We insist that you package all of the files for all questions for the entire assignment into a ZIP archive file. This can be done with a feature built into the Windows explorer (Windows), or with the zip terminal command (LINUX and Mac).  We cannot accept any other archive formats.  This means no tar, no gzip, no 7zip, no RAR. Non-zip archives will not be graded. We will not grade assignments if these submission instructions are not followed.

LinkedNode280: The node class used for a singly-linked list.

BilinkedNode280: An extension of LinkedNode280 that adds the "previous node" reference re-

quired 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 al-

low stepping backwards, such as goBack() and goLast().

LinkedIterator: An implementation of LinearIterator280 which is an iterator object for a singly-

linked 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 LinearItera-

tor280 interface. The Nodes of the list are LinkedNode280 objects, and it can provide iterators of of type LinkedIterator.

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 record additional positions in the list in the form of iterators should we so desire.

Question 1 (4 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 141 or CMPT 214. Jack wants to simulate the loading of cargo onto his ships so he can track how much of one type of grain is on a given ship, and to make sure that his ships are not overloaded.2

In this problem you will be given a list-of-lists data structure.  It will be a list of Ship objects, each of which contains a list of Sack objects. Each Sack object represents one sack of a particular type of grain.

The type of grain in a sack is represented by a value of type Grain, where Grain is an enumeration.

Enumerations

In this question use a data type in Java called an enumeration to represent the type of grain in a sack. 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 use an enumeration to define five constants to denote what type of grain is in a sack:

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:

✝

You’ll need to use one of the values from the Grain enumeration in task 3, below.

Description of Files Provided

You are provided with three Java files:

Sack.java: Contains the class Sack which is an object that represents a sack of grain. A sack of grain has a grain type, and a weight (in pounds). This object is complete and you will not need to edit this file, but you should familiarize yourself with its data and methods. This file also contains the definition of the enumerated type Grain.

Ship.java: Contains the class Ship which represents a ship in Jack’s fleet.  Each ship has a name, a capacity (weight in pounds), and contains a list of Sack objects which represent the ship’s cargo. This class contains two unfinished methods that you will write (see below). Familiarize yourself with the other methods and instance variables of this class.

CargoSimulator.java This file contains the CargoSimulator class. This class generates the data you’ll be working with for this question.  Its constructor generates a list of ships and fills them with sacks of grain. You’ll be writing some code in the main() method of this class (see below).

Your Tasks

1. In Ship .java, complete the isOverloaded method.  This method must return a boolean value true if the ship is overloaded, and false otherwise. The ship is overloaded if the total weight of all sacks of grain in its cargo exceeds the ship’s capacity.

2. In Ship .java, complete the sacksOfGrainType method. This method must return the number of sacks of grain of the grain type indicated by its parameter that are in the ship’s cargo. That is, if the parameter type is Grain .WHEAT and the ship’s cargo contains 42 sacks of wheat, the method should return 42.

3. In the main() method of CargoSimulator .java, there is an instance of a CargoSimulator object called sim. As described above, this object contains a list of ships, and each ship contains its list of cargo. At the location indicated, print out how many sacks of wheat each ship in sim is carrying.

4. In the main() method of CargoSimulator .java, print out a message for each ship in the CargoSimulator instance sim that is overloaded. If a ship is not overloaded, print nothing.

Implementation Notes

Upon inspection of the constructor for CargoSimulator, it may appear that the data is being randomly generated. The data is “randomly” generated, but a fixed random seed is used to ensure that the same random instance of the data is generated every time the program is run. Thus, you should expect that the data will always be the same, and that you will get the same answer every time. That said, it is possible that different computers and/or operating systems will generate different data. However, on the same machine within the same operating system, the same data will be generated every time.

Sample Output

Here is what the output might look like.  This demonstrates the form of the output only, and not the expected numbers.  The exact numbers may depend on the random number generator for your operating system.

Question 2 (12 points):

Your Tasks

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 com- ment. Write code to implement each of these unfinished method.

Implementation Notes

The javadoc headers for each method explain what each method is supposed to do3.  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.

When implementing the methods, consider carefully any special cases that might cause need to update the cursor position, or ensure that it remains in a valid state.

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 (12 points):

Your Tasks

Write a regression test for the BilinkedList280 class. You only need to test the methods that you had to write in question 2. You may generate test cases using white-box, black-box, or a combination of both methods.

Comment your regression test code. Each test case should be clearly identifiable from the comments, and the comments should indicate which method(s) you are testing, the purpose of the test, and the condition(s) under which you are testing it/them.

Implementation Notes

Again, write the code for this question within 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 are 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.