Dynamic data structures are one of the most helpful tools for programmers managing both the
planning process and the management of memory that they use for their programs. As you’ve
seen in lecture, the ArrayList allows the user to add elements without needing to worry about
the size of the underlying array: if the array needs more space, a new array will be created to
handle new data without our guidance. Similarly, a LinkedList allows the user to add elements
without needing to worry about the constraints of an array: the LinkedList allows for virtually
unlimited elements to be added without changing constraints (limited, of course, by your
This homework assignment introduces a dynamic data structure that combines Arrays and
LinkedLists. The Train is a type of LinkedList that allows the user to connect standalone units of
The Train is a LinkedList composed of two different objects: the Car and the Train.
The Car object is, itself, a static data structure. Each Car object holds a single array of elements
referred to as cargo. Like a standard train car, this array will remain the same size for a single
instance of a Car object, hence the static description for this structure. A position in the cargo
array is considered “empty” if it is null.
Each Car also has a reference to the car behind it, if one exists, referred to as the nextCar. This
will be your means of creating a Train, as a train is composed of a sequence of train cars linked
Figure 1. Simple diagram of a Car object
A Car is capable of performing actions without being connected to a Train, so we will be
providing it with some methods of its own. The table below describes the functionality of the
Car’s methods; see the skeleton for more details including edge cases.
Car The Car’s constructor simply starts the instance with an empty array capable of
holding a number of elements according to the parameter.
addCargo Adds the passed object’s reference to the Car’s cargo array. Cargo should be
added to the first “empty” (null) space in the Car. You should not move any of
the other cargo.
getCargo Returns a reference to this Car’s array of cargo.
capacity Returns the maximum capacity of this Car (the length of the cargo array).
size Returns the current number of objects stored in this Car.
get For a passed index, this method returns a reference to the object at that location
in the Car’s cargo array.
set For a passed index and object reference, this method replaces the object at the
provided index in the Car’s cargo array with the passed object (null is permitted).
isFull Returns a boolean value based on whether each position in the Car’s cargo array
setNextCar Sets this Car’s nextCar to reference the Car that will be following this Car..
getNextCar Returns the Car linked to by this Car.
The Train object will be our dynamic data structure. Unlike Cars, Trains are limited to holding
objects of type Car. However, the bonus is that different Cars can hold different types of objects,
meaning you can have a Train carrying many kinds of cargo.
Like the LinkedList you’ve learned about, the Train maintains two references: a head and a tail,
referred to respectively as the engine and the caboose. The engine will refer to the first car in
the Train, while the caboose will refer to the last car in the Train. Both will refer to null if no cars
Lastly, we’ll want the Train to be capable of adding cargo without requiring the user to manually
create new Cars. To do so, we specify a newCarSize for Cars that are created automatically
when there is no space on the Train.
Figure 2. Simple Diagram of a Train Object with three cars
The Train will have some of the expected functionalities of a LinkedList, but with the added twist
of working with Cars. The table below describes the functionalities of the Train’s methods; see
the skeleton code for more details, including edge cases.
Train (no arguments) Creates a new Train with no Cars. engine and caboose
should point to null.
Train (one argument) Creates a new Train with the array of Cars provided. The
Cars will be added to the Train in the same order that they
are presented in the array. You may assume that none of
the Cars are already connected to another Car.
getNewCarSize Returns the size of new Cars created by the Train.
setNewCarSize Sets the size of new Cars created by the Train.
getEngine Returns the first Car in the Train.
getCaboose Returns the last Car in the Train.
size Returns the number of Cars in the Train. You will need to
iterate through the Cars in this Train to count them.
get (one argument) Returns the Car at the given position in the Train.
get (two arguments) Returns the cargo in the Car at the given position in the
appendCar (car argument) Adds the passed car to the end of the Train, making it the
new caboose, and the Car previously linked to that car
should be removed. You do not need to check if this Car is
already a part of the Train.
appendCar (cargo argument) Adds an empty new Car to the end of the Train according to
the size specified by newCarSize. Ignore the cargo
argument: it exists in the skeleton code but was left for the
sake of tests working.
set For a passed index and object reference, this method
replaces the object for the specified Car at the provided
index in the Car’s cargo array with the passed object.
addCargo Adds the parameter to the first open space in a Car on the
Train. You do not need to check if the parameter is already
on the Train. Creates a new Car if there is no Car on this
Train that can store the cargo.
emptyTrainCars Removes references to all objects from each Car on the
Train. The Cars should remain connected and the Train
should continue to have access to them.
boilerUp Prints “Toot toot!\n”.
FullCarException is an exception class that has been implemented for you. You will be
required to throw the FullCarException when attempting to add cargo to a full car. The message
for the exception is up to you.
To receive credit for this assignment, you must abide by the following constraints:
● You may not create any additional classes besides Car, Train, and FullCarException.
● You may not create additional fields for any of the Car, Train or FullCarException
● You may not modify the declarations of the fields for either Car or Train.
● The methods are presented above and in the skeleton in the order by which the
assignment is most easily completed.
● It is recommended that you try each of your methods after you develop them.
● Many of the methods for Train will require you to iterate through elements that are linked
by object references rather mapped to positions in an array. Once you figure this out,
you will be able to complete all the methods. Consider how you can keep track of your
location on the Train and know when you’ve reached the end as you traverse it.
For this assignment, you are required to submit ONLY the following source files for automatic
Your code must compile or you will not receive credit for this assignment.
Points for this assignment will be distributed as follows:
Methods for Car and Train will be automatically tested. As an added challenge, the same Cars
and Train will running non-stop through all your test cases. This means that if you fail a test,
there is a significant chance your remaining test cases will derail and consequently fail. You’ll
want to fix the first test case failure reported before resubmission.
The testing system used may report these failures out of order, but they have been numbered in
the case this should occur (with test 01 occurring first, then 02, and so on).