Programming Languages and Techniques
Homework 10 : Battleship
(Deadline as per Canvas)
For HW10, you may work as a group (no more than 2 students). Please mention your
collaborator’s name at the top of each of your code files.
This homework is more detailed than previous assignments, so start as early as you can on
it. It deals with the following topics:
● Inheritance & overriding
● Access modifiers
● Abstract classes (we’ll learn about these in the next lecture)
● 2-dimensional arrays
Introduction
We are going to show you how to build a simple (only because there is no graphical user
interface - GUI) version of the classic game Battleship.
Battleship is usually a two-player game, where each player has a fleet of ships and an ocean
(hidden from the other player), and tries to be the first to sink the other player's fleet.
We will be doing just a one-player vs. computer version, where the computer places the
ships, and the human attempts to sink them.
We'll play this game on a 10x10 “ocean” and will be using the following ships (“the fleet”):
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Programming Languages and Techniques
How to Play Battleship
Please take a look at these rules even if you have played Battleship before in your life.
Remember this is a Human vs. Computer version.
The computer places the ten ships on the ocean in such a way that no ships are immediately
adjacent to each other, either horizontally, vertically, or diagonally. Take a look at the following
diagrams for examples of legal and illegal placements:
The human player does not know where the ships are. The initial display of the ocean printed
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Programming Languages and Techniques
to the console therefore shows a 10 by 10 array of ‘.‘ (see the description of the Ocean class’
print() method below for more information on what subsequent ocean displays will look
like).
The human player tries to hit the ships, by indicating a specific row and column number (r,c).
The computer responds with one bit of information saying, “hit” or “miss”.
When a ship is hit but not sunk, the program does not provide any information about what kind
of a ship was hit. However, when a ship is hit and sinks, the program prints out a message “You
just sank a ship - (type).” After each shot, the computer re-displays the ocean with the new
information.
A ship is “sunk” when every square of the ship has been hit. Thus, it takes four hits (in four
different places) to sink a battleship, three to sink a cruiser, two for a destroyer, and one for a
submarine.
The object is to sink the fleet with as few shots as possible; the best possible score would be
20 (lower scores are better.) When all ships have been sunk, the program prints out a message
that the game is over, and tells how many shots were required.
Details of Implementation
Name your project Battleship, and your package battleship.
Your program should have the following 8 classes:
● class BattleshipGame
o This is the “main” class, containing the main method, which starts by creating an
instance of Ocean
● class Ocean
o This contains a 10x10 array of Ships, representing an “ocean”, and some
methods to manipulate it
● abstract class Ship
o This abstract class describes the characteristics common to all ships
o It has subclasses:
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Programming Languages and Techniques
▪ class Battleship extends Ship
● Describes a ship of length 4
▪ class Cruiser extends Ship
● Describes a ship of length 3
▪ class Destroyer extends Ship
● Describes a ship of length 2
▪ class Submarine extends Ship
● Describes a ship of length 1
▪ class EmptySea extends Ship
● Describes a part of the ocean that doesn’t have a ship in it. (It
seems silly to have the lack of a ship be a type of ship, but this is a
trick that simplifies a lot of things. This way, every location in the
ocean contains a “ship” of some kind.)
Abstract class Ship
The abstract Ship class has the instance variables below.
Note: Fields should be declared private unless there is a good reason for not doing so. This is
known as “encapsulation”, which is the process of making the fields in a class private and
providing access to the fields via public methods (e.g. getters and setters).
● private int bowRow
o The row that contains the bow (front part of the ship)
● private int bowColumn
o The column that contains the bow (front part of the ship)
● private int length
o The length of the ship
● private boolean horizontal
o A boolean that represents whether the ship is going to be placed horizontally or
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Programming Languages and Techniques
vertically
● private boolean[] hit
o An array of booleans that indicate whether that part of the ship has been hit or
not
The default constructor for the Ship class is:
● public Ship(int length)
o This constructor sets the length property of the particular ship and initializes
the hit array based on that length
The methods in the Ship class are the following:
Getters
● public int getLength()
o Returns the ship length
● public int getBowRow()
o Returns the row corresponding to the position of the bow
● public int getBowColumn()
o Returns the bow column location
● public boolean[] getHit()
o Returns the hit array
● public boolean isHorizontal()
o Returns whether the ship is horizontal or not
Setters
● public void setBowRow(int row)
o Sets the value of bowRow
● public void setBowColumn(int column)
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Programming Languages and Techniques
o Sets the value of bowColumn
● public void setHorizontal(boolean horizontal)
o Sets the value of the instance variable horizontal
Abstract Methods
● public abstract String getShipType()
o Returns the type of ship as a String. Every specific type of Ship (e.g.
BattleShip, Cruiser, etc.) has to override and implement this method and
return the corresponding ship type.
Other Methods
● boolean okToPlaceShipAt(int row, int column, boolean horizontal,
Ocean ocean)
o Based on the given row, column, and orientation, returns true if it is okay to put a
ship of this length with its bow in this location; false otherwise. The ship must not
overlap another ship, or touch another ship (vertically, horizontally, or diagonally),
and it must not ”stick out” beyond the array. Does not actually change either the
ship or the Ocean - it just says if it is legal to do so.
● void placeShipAt(int row, int column, boolean horizontal, Ocean
ocean)
o “Puts” the ship in the ocean. This involves giving values to the bowRow,
bowColumn, and horizontal instance variables in the ship, and it also involves
putting a reference to the ship in each of 1 or more locations (up to 4) in the ships
array in the Ocean object. (Note: This will be as many as four identical
references; you can’t refer to a ”part” of a ship, only to the whole ship.)
o For placement consistency (although it doesn’t really affect how you play the
game), let’s agree that horizontal ships face East (bow at right end) and vertical
ships face South (bow at bottom end).
▪ This means, if you place a horizontal battleship at location (9, 8) in the
ocean, the bow is at location (9, 8) and the rest of the ship occupies
locations: (9, 7), (9, 6), (9, 5).
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Programming Languages and Techniques
▪ If you place a vertical cruiser at location (4, 0) in the ocean, the bow is at
location (4, 0) and the rest of the ship occupies locations: (3, 0), (2, 0).
● boolean shootAt(int row, int column)
o If a part of the ship occupies the given row and column, and the ship hasn’t been
sunk, mark that part of the ship as “hit” (in the hit array, index 0 indicates the
bow) and return true; otherwise return false.
● boolean isSunk()
o Return true if every part of the ship has been hit, false otherwise
● @Override
public String toString()
o Returns a single-character String to use in the Ocean’s print method. This method
should return ”s” if the ship has been sunk and ”x” if it has not been sunk. This
method can be used to print out locations in the ocean that have been shot at; it
should not be used to print locations that have not been shot at. Since toString
behaves exactly the same for all ship types, it is placed here in the Ship class.
Class ShipTest
This is the JUnit test class for the Ship class. The ShipTest.java file we have provided contains
SOME of the unit tests for this assignment. There will be more tests for the Ship class that
we will be running your program against. Import ShipTest.java into your Java project and
implement enough code in the methods in your program to pass all tests.
Generate additional scenarios and add test cases to each test method. You should have a total
of at least 3 distinct scenarios and valid test cases per method (including the ones provided).
For example, one scenario could be, you create and place a battleship in a particular location in
the ocean by calling its placeShipAt method. Then you create a destroyer and see if it can be
placed in a particular location by calling its okToPlaceShipAt method. If so, you place it. Then
you create a cruiser and see if it can be placed in a particular location by calling its
okToPlaceShipAt method. If so, you place it.
Test every non-private method in the Ship class. (Unfortunately, you can’t test methods that
are private because they are inaccessible outside of the class.)
Also test the methods in each subclass of Ship. You can test the Ship method and its
subclasses in the same file.
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You must include comments to explain your different testing scenarios.
Class BattleshipGame
The BattleshipGame class is the “main” class -- that is, it contains a main method. In this
class you will set up the game; accept ”shots” from the user; display the results; and print final
scores. All input/output is done here (although some of it is done by calling a print() method
in the Ocean class.) All computation will be done in the Ocean class and the various Ship
classes.
To aid the user, row numbers should be displayed along the left edge of the array, and column
numbers should be displayed along the top. Numbers should be 0 to 9, not 1 to 10. The top
left corner square should be 0, 0. Use different characters to indicate locations that contain a
hit, locations that contain a miss, and locations that have never been fired upon.
For example, here’s a display of the ocean when the program first launches, and no shots have
been fired.
Use various sensible methods. Don’t cram everything into one or two methods, but try to
divide up the work into sensible parts with reasonable names.
Extending abstract class Ship
Use the abstract Ship class as a parent class for every single ship type. Create the following
classes and keep each class in a separate file.
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Programming Languages and Techniques
● class Battleship extends Ship
● class Cruiser extends Ship
● class Destroyer extends Ship
● class Submarine extends Ship
Each of these classes has a zero-argument public constructor, the purpose of which is to set
the length variable to the correct value. From each constructor, call the constructor in the
super class with the appropriate hard-coded length value for each ship. Note: You can store
the hard-coded int values in static final variables.
Aside from the constructor you have to override this method:
● @Override
public String getShipType()
o Returns one of the strings “battleship”, “cruiser”, “destroyer”, or
“submarine”, as appropriate. Again, these types of hard-coded string values
are good candidates for static final variables.
o This method can be useful for identifying what type of ship you are dealing with,
at any given point in time, and eliminates the need to use instanceof
Class EmptySea extends Ship
You may wonder why “EmptySea” is a type of Ship. The answer is that the Ocean
contains a Ship array, every location of which is (or can be) a reference to some Ship. If a
particular location is empty, the obvious thing to do is to put a null in that location. But this
obvious approach has the problem that, every time we look at some location in the array, we’d
have to check if it is null. By putting a non-null value in empty locations, denoting the
absence of a ship, we can save all that null checking.
The constructor for the EmptySea class is:
● public EmptySea()
o This zero-argument constructor sets the length variable to 1 by calling the
constructor in the super class
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Programming Languages and Techniques
The methods in the EmptySea class are the following:
● @Override
boolean shootAt(int row, int column)
o This method overrides shootAt(int row, int column) that is inherited
from Ship, and always returns false to indicate that nothing was hit
● @Override
boolean isSunk()
o This method overrides isSunk() that is inherited from Ship, and always
returns false to indicate that you didn’t sink anything
● @Override
public String toString()
o Returns the single-character “-“ String to use in the Ocean’s print method.
(Note, this is the character to be displayed if a shot has been fired, but nothing
has been hit.)
● @Override
public String getShipType()
o This method just returns the string “empty”
Class Ocean
Instance variables
● private Ship[][]ships = new Ship[10][10]
o Used to quickly determine which ship is in any given location
● private int shotsFired
o The total number of shots fired by the user
● private int hitCount
o The number of times a shot hit a ship. If the user shoots the same part of a ship
more than once, every hit is counted, even though additional “hits” don’t do the
user any good.
● private int shipsSunk
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Programming Languages and Techniques
o The number of ships sunk (10 ships in all)
Constructor
● public Ocean()
o Creates an ”empty” ocean (and fills the ships array with EmptySea objects).
You could create a private helper method to do this.
o Also initializes any game variables, such as how many shots have been fired.
Methods
● void placeAllShipsRandomly()
o Place all ten ships randomly on the (initially empty) ocean. Place larger ships
before smaller ones, or you may end up with no legal place to put a large ship.
You will want to use the Random class in the java.util package, so look that
up in the Java API.
o To help you write the code for this method, reference the printWithShips()
method below. It will allow you to see where ships are actually being placed in the
Ocean while you are writing and debugging your program.
● boolean isOccupied(int row, int column)
o Returns true if the given location contains a ship, false if it does not
● boolean shootAt(int row, int column)
o Returns true if the given location contains a ”real” ship, still afloat, (not an
EmptySea), false if it does not. In addition, this method updates the number of
shots that have been fired, and the number of hits.
o Note: If a location contains a “real” ship, shootAt should return true every time
the user shoots at that same location. Once a ship has been ”sunk”, additional
shots at its location should return false.
● int getShotsFired()
o Returns the number of shots fired (in the game)
● int getHitCount()
o Returns the number of hits recorded (in the game). All hits are counted, not just
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the first time a given square is hit.
● int getShipsSunk()
o Returns the number of ships sunk (in the game)
● boolean isGameOver()
o Returns true if all ships have been sunk, otherwise false
● Ship[][] getShipArray()
o Returns the 10x10 array of Ships. The methods in the Ship class that take an
Ocean parameter need to be able to look at the contents of this array; the
placeShipAt() method even needs to modify it. While it is undesirable to
allow methods in one class to directly access instance variables in another class,
sometimes there is just no good alternative.
● void print()
o Prints the Ocean. To aid the user, row numbers should be displayed along the
left edge of the array, and column numbers should be displayed along the top.
Numbers should be 0 to 9, not 1 to 10.
o The top left corner square should be 0, 0.
o ‘x’: Use ‘x’ to indicate a location that you have fired upon and hit a (real) ship.
(reference the description of toString in the Ship class)
o ‘-’: Use ‘-’ to indicate a location that you have fired upon and found nothing
there. (reference the description of toString in the EmptySea class)
o ‘s’: Use ‘s’ to indicate a location containing a sunken ship. (reference the
description of toString in the Ship class)
o ‘.’: and use ‘.’ (a period) to indicate a location that you have never fired upon
o This is the only method in the Ocean class that does any input/output, and it is
never called from within the Ocean class, only from the BattleshipGame
class.
For example, here’s a display of the ocean after 2 shots have missed.
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Programming Languages and Techniques
And here’s a display of the ocean after 2 shots have missed, and 1 has hit a (real) ship.
To further help you understand how to write the code for this method, here’s the
(high-level) logic for printing the ocean:
for each location in the 10 by 10 array (the “ocean”)
● if the location contains a ship that is sunk or if the location has been shot at, and was hit
or nothing was found
○ print the ship itself -- this will call toString in the Ship class or any Ship
subclass which has toString defined (i.e. EmptySea)
● otherwise print “.”
● void printWithShips()
o USED FOR DEBUGGING PURPOSES ONLY.
o Like the print() method, this method prints the Ocean with row numbers
displayed along the left edge of the array, and column numbers displayed along
the top. Numbers should be 0 to 9, not 1 to 10. The top left corner square
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should be 0, 0.
o Unlike the print() method, this method shows the location of the ships.
This method can be used during development and debugging, to see where
ships are actually being placed in the Ocean. (The TAs may also use this
method when running your program and grading.) It can be called from the
BattleshipGame class, after creating the Ocean and placing ships in it.
o Be sure to comment out any call to this method before actually playing the
game and before submitting your Java project.
o ‘b’: Use ‘b’ to indicate a Battleship.
o ‘c’: Use ‘c’ to indicate a Cruiser.
o ‘d’: Use ‘d’ to indicate a Destroyer.
o ‘s’: Use ‘s’ to indicate a Submarine.
o ‘ ‘: Use ‘ ’ (single space) to indicate an EmptySea.
For example, here’s a display of the ocean after creating the Ocean, calling
placeAllShipsRandomly, and then calling printWithShips.
You are welcome to write additional methods of your own. Additional methods should have
default access (accessible anywhere in the package) and be tested, if you think they have some
usefulness outside of this class. If you don’t think they have any use outside of this class, mark
them as private.
Class OceanTest
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This is the JUnit test class for the Ocean class. The OceanTest.java file we have provided
contains SOME of the unit tests for this assignment. There will be more tests for the Ocean
class that we will be running your program against. Import OceanTest.java into your Java
project and implement enough code in the methods in your program to pass all tests.
Generate additional scenarios and add test cases to each test method. You should have a total
of at least 3 distinct scenarios and valid test cases per method (including the ones provided).
For example, a scenario could be, you create and place a submarine in a particular location in
the ocean by calling its placeShipAt method. Then you check if a particular location in the
ocean is occupied by calling its isOccupied method. Create and place another submarine in a
particular location by calling its placeShipAt method. Then check if another location in the
ocean is occupied by calling its isOccupied method.
Test every required method for Ocean, including the constructor, but not including the
print() method. If you create additional methods in the Ocean class, you must either make
them private, or write tests for them.
Note: Two test methods have been completely implemented for you, meaning, no additional
test cases are required. (Of course, you’re welcome to add more!). These are testEmptyOcean
and testPlaceAllShipsRandomly.
testEmptyOcean tests if every location in an empty ocean is “empty”. Since it’s the constructor
in the Ocean class that is responsible for creating an ”empty” ocean (and filling the ships array
with EmptySeas), the testEmptyOcean method can be considered the test method for the
Ocean class constructor.
testPlaceAllShipsRandomly tests that the correct number of each ship type is placed in the
ocean after calling placeAllShipsRandomly.
You must include comments to explain your different testing scenarios.
What to Submit
Please submit all the Java classes in your Java project. Make sure to include everything in your
“src” folder.
If you’re working as part of a team, only one student from your team needs to submit the files.
Include the members of your team as part of the @author tag in the Javadocs for each class. If
Brandon was working with Sarah, their Javadocs and @author tag would look something like:
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Evaluation
You will be graded out of 52 points:
● Style (8 pts total)
o This includes, but is not limited to:
▪ Adding Javadocs to every class, method, and variable, and comments to
all non-trivial code.
▪ Indenting properly (Cmd+i or Ctrl+i) and using { brackets } correctly in
loops and conditionals
▪ Naming additional variables and methods descriptively with camelCase
▪ Removing unused variables and commented out code blocks/print
statements used for debugging
● Game play (10 pts total)
o This comes down to whether or not a TA can play your game. The interface
should be clear. If you have made some potentially unusual design choice, please
make sure that you point that out very clearly. If you do not know what this
means, it might be worth asking on EdDiscussion or during office hours. If you
followed all the instructions to the letter, you are fine.
● Unit testing (24 pts total)
o Please make sure you pass the provided tests as well as your own additional unit
tests (10 pts)
o Passing our own unit tests (14 pts)
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o Note, there are some methods which cannot be unit tested, such as a method that
takes in user input. Similarly, a method that prints to the console (and does only
that) cannot be unit tested.
o Note: please clearly comment on your unit tests to explain the different scenarios
that you are testing. The TAs will read your tests to make sure they are distinct
and valid.
● Code writing (10 pts)
o Make sure you understand inheritance and correctly utilize overriding
o Note: Please clearly comment on your placeAllShipsRandomly() method.
The TAs will read this part of your code and make sure that you are actually doing
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