Purpose of this assignment

• To give you more experience with classes and inheritance.

General idea of the assignment

Once again, this assignment is based on a game, since games are a good source of relatively simple problems.

The Ocean (10x10)

The Fleet One battleship S S S S Two cruisers S S S     S S S Three destroyers S S     S S     S S Four submarines S     S     S     S

Battleship is usually a two-player game, where each player has a fleet and an ocean (hidden from the other player), and tries to be the first to sink the other player's fleet. We'll just do a solo version, where the computer places the ships, and the human attempts to sink them.

How to play

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. For example,

Legal arrangement	Illegal--ships diagonally adjacent	Illegal--ships horizontally adjacent
S S S     S                   S     S S   S S S         S                       S S   S     S                       S                   S                   S S                 S	S S S     S                   S     S S   S S S         S                       S S   S                             S                   S                   S S                 S	S S S     S                   S     S S   S S S         S                       S S   S                             S                   S                   S S                 S

The human player does not know where the ships are. The initial display of the ocean shows a 10 by 10 array of locations, all the same.

The human player tries to hit the ships, by calling out a row and column number. The computer responds with one bit of information--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 redisplays 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. (Low 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

Name your project Battleship, and your package battleship.

The classes

Your program should have the following classes:

• class BattleshipGame -- This is the "main" class, containing the main method and a variable of type Ocean.
• class Ocean -- This contains a 10x10 array of Ships, representing the "ocean," and some methods to manipulate it.
• class Ship -- This describes characteristics common to all the ships. It has subclasses:
  • 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.)

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; print final scores; and ask the user if he/she wants to play again. 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.

Use methods. Don't cram everything into one or two methods, but try to divide up the work into sensible parts with reasonable names.

class ShipTest

Test every non-private method in the Ship class. TDD (Test-Driven Design is highly recommended.)

Also test the methods in each subclass of Ship. You can do this here or in separate test classes, as you wish.

class Ship

Since we don't really care which end of a ship is the bow and which the stern, we will consider all ships to be facing up or left. Other parts of the ship are in higher-numbered rows or columns.

You don't need to write a constructor for this class--Java will automatically supply one for you (with no arguments).

Instance variables

int bowRow -- the row (0 to 9) which contains the bow (front) of the ship.
int bowColumn -- the column (0 to 9) which contains the bow (front) of the ship.
int length -- the number of squares occupied by the ship. An "empty sea" location has length 1.
boolean horizontal -- true if the ship occupies a single row, false otherwise.
boolean [] hit = new boolean[4]; -- an array of booleans telling whether that part of the ship has been hit. Only battleships use all four locations; cruisers use the first three; destroyers 2; submarines 1; and "empty sea" either one or none.

int getLength()

Returns the length of this particular ship. This method exists only to be overridden, so it doesn't much matter what it returns; an abstract "ship" doesn't have a fixed length.

Getters:

int getBowRow() -- Returns bowRow
int getBowColumn() -- Returns bowColumn
boolean isHorizontal() -- Returns horizontal

Setters:

void setBowRow(int row) -- Sets the value of bowRow
void setBowColumn(int column) -- Sets the value of bowColumn
void setHorizontal(boolean horizontal) -- Sets the value of the instance variable horizontal.

String getShipType()

Returns the type of this ship. This method exists only to be overridden, so it doesn't much matter what it returns.

boolean okToPlaceShipAt(int row, int column, boolean horizontal, Ocean ocean)

Returns true if it is okay to put a ship of this length with its bow in this location, with the given orientation, and returns 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, just says whether it is legal to do so.

void placeShipAt(int row, int column, boolean horizontal, Ocean ocean)

"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.)

boolean shootAt(int row, int column)

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, 0 indicates the bow) and return true, otherwise return false.

boolean isSunk()

Return true if every part of the ship has been hit, false otherwise.

class Battleship extends Ship
class Cruiser extends Ship
class Destroyer extends Ship
class Submarine extends Ship

Each of these classes has a constructor, the purpose of which is to set the inherited length variable to the correct value, and to initialize the hit array.

@Override
String getShipType()

Returns one of the strings "battleship", "cruiser", "destroyer", or "submarine", as appropriate.

@Override
public String toString()

Returns a single-character String to use in the Ocean's print method (see below).

This method should return "x" if the ship has been sunk, "S" 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 can be moved into the Ship class, and simply inherited by each individual type of ship.

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 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.

EmptySea()

This constructor sets the inherited length variable to 1.

@Override
boolean shootAt(int row, int column)

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()

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()

Returns a single-character String to use in the Ocean's print method (see below).

class OceanTest

This is a JUnit test class for Ocean. Test every required method for Ocean, including the constructor, but not including the print() method. If you create additonal methods in the Ocean class, you must either make them private, or write tests for them. Test methods do not need comments, unless they do something non-obvious.

Experience has shown that it is a bad idea for one partner to write the tests and the other partner to write the code. It works much better if you write tests for your own code.

class Ocean

Instance variables

Ship[][] ships = new Ship[10][10] -- Used to quickly determine which ship is in any given location.
int shotsFired -- The total number of shots fired by the user.
int hitCount -- 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 the additional "hits" don't do the user any good.
int shipsSunk -- The number of ships sunk (10 ships in all).


Ocean()

The constructor. Creates an "empty" ocean (fills the ships array with EmptySeas). Also initializes any game variables, such as how many shots have been fired.

void placeAllShipsRandomly()

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.

boolean isOccupied(int row, int column)

Returns true if the given location contains a ship, false if it does not.

boolean shootAt(int row, int column)

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.
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()

Returns the number of shots fired (in this game).

int getHitCount()

Returns the number of hits recorded (in this game). All hits are counted, not just the first time a given square is hit.

int getShipsSunk()

Returns the number of ships sunk (in this game).

boolean isGameOver()

Returns true if all ships have been sunk, otherwise false.

Ship[][] getShipArray()

Returns the 10x10 array of ships. The methods in the Ship class that take an Ocean parameter really 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()

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. The top left corner square should be 0, 0. Use 'S' to indicate a location that you have fired upon and hit a (real) ship, '-' to indicate a location that you have fired upon and found nothing there, 'x' to indication location containing a sunken ship, and '.' to indicate a location that you have never fired upon.

This is the only method in the Ocean class that does any input/output, and it is never called from within the Ocean class (except possibly during debugging), only from the BattleshipGame class.

You are welcome to write additional methods of your own. Additional methods should either be tested (if you think they have some usefulness outside this class), or private (if they don't).

Additional requirements:

• Every method, except your test methods, should have javadoc comments. Use Eclipse's Source -> Generate Element Comment to get the correct form.
  
• The program should be properly formatted. Use Eclipse's Source -> Format to get it right.
  
• Every method should be short enough to see all at once on the screen.
  

Due date:

Friday, November 15, before 6am. Zip your entire project and submit it via Canvas.