Description
Introduction
For this assignment you are to extend your game from Assignment #1 (A1) to incorporate
several important design patterns, and a Graphical User Interface (GUI). The rest of the game
will appear to the user to be similar to the one in A1, and most of the code from A1 will be
reused, although it will require some modification and reorganization.
An important goal for this assignment will be to reorganize your code so that it follows the
Model-View-Controller (MVC) architecture. If you followed the structure specified in A1, you
should already have a “controller”: the Game class containing the getCommand() method
along with methods to process the various commands (most of which call methods in
GameWorld). The GameWorld class becomes the “data model”, containing the collection of
game objects and other game state information. You are also required to add two classes
acting as “views”: a score view which will be graphical, and a map view which for now will
retain the text-based form generated by the ‘m’ command in A1 (in A3 we will replace the textbased map with an interactive graphical map).
Most of the keyboard commands from A1 will be replaced by GUI components (menus,
buttons, etc.). Each such component will have an attached “command” object, and the
command objects will perform the same operations as previously performed by the keyboard
commands.
The program must use appropriate interfaces for organizing the required design patterns.
The following design patterns are to be implemented in this assignment:
Observer/Observable – to coordinate changes in the model with the various views,
Iterator – to walk through all the game objects when necessary,
Command – to encapsulate the various commands the player can invoke,
Singleton – to insure that only a single copy of each command object exists,
Strategy – to control movement for additional (non-player) cars, and
Model Organization
The “game object” hierarchy will be the same as in A1. GameWorld is to be reorganized
(if necessary) so that it contains a collection of game objects implemented in a single collection
data structure. The game object collection is to implement the Collection interface and
provide for obtaining an Iterator. All game objects are to be contained in this single
collection data structure1
. The iterator for the collection returns one game object for each call
to its getNext() method.
1
If you did not implement your game object collection this way in Asst #1 you must change it for this assignment.
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The model is also to contain the same game state data as A1, plus a new state value: a
flag indicating whether Sound is ON or OFF (described below).
Views
A1 contained two functions to output game information: the ‘m’ key for outputting a “map”
of the game objects in the GameWorld, and the ‘d’ key for outputting current game state data
(time, lives, etc.) Each of these two operations is to be implemented in this assignment as a
view of the GameWorld model. To do that, you will need to implement two new classes: a
MapView class containing code to output the map, and a ScoreView class containing code to
output the current score and other state information.
To implement this, GameWorld should be defined as an observable, with two observers–
MapView and ScoreView. Each of these should be “registered” as an observer of
GameWorld. When the controller invokes a method in GameWorld that causes a change in the
world (such as a game object moving, or a new object being added to the world) the
GameWorld notifies its observers that the world has changed. Each observer then
automatically produces a new output view of the data it is observing – the game world objects
in the case of MapView, and a description of the game state values in the case of ScoreView.
The MapView output for this assignment is unchanged from A1: text output on the console
showing all game objects which exist in the world. However, the ScoreView is to present a
graphical display of the game state values (described in more detail below).
In order for a view (observer) to produce the new output, it will need access to some of
the data in the model. This access is provided by passing to the observer’s update() method
a parameter that is a reference back to the model. This has the undesirable side-effect that the
view has access to the model’s mutators. We will see later how to fix this problem.
Non-Player Cars (NPCs)
The game initialization code should create and add to the game world three additional
instances of Car (so that there are now four cars – the player’s car plus three “non-player
cars”. Each NPC is to have an initial location which is “near” the first pylon, but not exactly at
the first pylon; instead, each NPC should be at least several car lengths away from the first
pylon (this is to make sure that the NPCs are not colliding with the player’s car to start with).2
When an NPC collides with the player’s car, the player’s car sustains damage just as
described in A1 – including that if the car sustains so much damage that it can no longer move
the player loses a life, and the world is reinitialized. NPCs also sustain damage when they
collide, but you should initialize them with much higher values so that they can compete longer
(consider NPCs to be “armored” so that they can sustain more damage).
NPCs will be controlled by separate pieces of code called strategies which can be altered
using a new “Change Strategies” command; this is described under “Strategy Pattern”, below.
2
You may if you wish apply additional constraints to the NPC’s initial locations. For example, you could compute
a “starting line” intersecting the first pylon and perpendicular to the line from the first to the second pylon, and
require that the initial position of each NPC be behind that line in relation to the position of the second pylon.
This would make for a much fairer game. However, this is not a requirement; the only requirement is that initial
NPC locations be such that the NPCs do not overlap the player’s car.
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GUI Operations
The program is to be modified so that the top-level Game class extends (“is-a”) JFrame
representing the GUI for the game. The JFrame should be divided into three areas: one for
commands, one for “score” (game state) information, and one for the “map” (which will be an
empty JPanel for now but in subsequent assignments will be used to display the map in
graphical form). See the sample picture at the end. Note that since user input is via GUI
components, flow of control will now be event-driven and there is no longer any need to invoke
a “play()” method – once the Game is constructed it simply waits for user-generated input
events. Note however that it is still a requirement to have a “Starter” class containing the
main() method.
In A1 your program prompted the player for commands in the form of keyboard input
characters. For this assignment the code which prompts for commands and reads keyboard
command characters is to be discarded. In its place, commands will be input through three
different mechanisms: on-screen buttons, key bindings, and menu items. Some commands
will be invokable only via a single one of these mechanisms, while others will be able to be
invoked in multiple ways. You are to create singleton command objects (see below) for each
of the commands from A1 plus the new change strategies command, and attach the objects as
commands to various combinations of invokers as shown in the following table. An ‘x’ in a
column indicates that the command in that row is to be able to be invoked by the mechanism in
the column header. Further details regarding this are given below.
Command KeyBinding MenuItem Button
accelerate x
brake x
left turn x
right turn x
collide with NPC x
collide with pylon x
fuel pickup x x
collide with Bird (g) x
enter oil slick x
exit oil slick x
add oil slick x x
new colors x
tick x x
quit x x x
Change Strategies x x
As shown in the table, some commands will be invoked by GUI buttons. You will need a
class that extends JPanel and contains these buttons. You are to create the appropriately
labeled buttons, add them to the panel, and add the panel as a component of the game
(JFrame). Each button is to have an appropriate command object attached to it, so that when
a button gets pushed it invokes the “action performed” method in the corresponding command
object (the “execute” method in terms of the Command pattern), which contains the code to
perform the command.
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Most commands execute exactly the same code as was implemented in A1. One
exception is the ‘p’ (player hit pylon) command. Previously this command consisted of three
characters typed on the keyboard: pxx, where xx is the number of the pylon the player car
has driven over. Now, the ‘p’ button command is to use the static method
JOptionPane.showInputDialog to display a modal input dialog box which allows the user
to enter the value xx. When the user clicks “OK”, the typed value is returned as a String; at
this point it can be processed similarly to the way your code from A1 handled the input string.
For example:
String inputString = JOptionPane.showInputDialog(“Please input a pylon number”);
int pylonNum = Integer.parseInt(inputString);
Note that showInputDialog() throws NumberFormatException if the user inputs a nonnumeric value; your program should handle this gracefully. Note also that
showInputDialog() has additional forms which allow you to manage the form of the
displayed dialog in more detail; this would be nice but is not required.
The other command which must operate slightly different in this assignment is ‘c’
(player’s car collided with another car). In A1, this command just increased the damage level
of the player’s car. Now, the command is to also add damage to one of the non-player cars:
the ‘c’ command code should choose one NPC and increase that NPC’s damage as well. To
make the game more fair you should really alternate between NPCs when this command is
entered, but it is acceptable to use any algorithm (including choosing an NPC randomly, or
always choosing the same NPC). We will change how this works in the next assignment, so
any approach in A2 is fine.
Some commands will be invoked using the Java KeyBinding mechanism. For example,
your program is to arrange that the up arrow, down arrow, left arrow, and right arrow keys
invoke command objects corresponding to the code previously executed when the ‘a’, ‘b’, ‘l’,
and ‘r’ keys (for controlling the player’s car) were entered, respectively. Thus, up-arrow
performs acceleration, down-arrow performs braking (“slowing down”), left-arrow turns the
steering wheel left, and right-arrow turns the steering wheel right. Note that using key bindings
means that whenever a key is pressed, the program will immediately invoke the corresponding
action (without the user pressing the Enter key).
In addition, the program should bind the “space” key to the new “change strategies”
operation (see below), as well as binding the add oil slick, tick, and quit commands to the ‘o’,
‘t’, and ‘q’ keys respectively. If you want, you may also use key bindings to map any of the
other command keys from A1, but only the ones listed here are required.
Some commands will be invoked using menu items. Your GUI should contain at least two
menus: “File” and “Commands”. The Commands menu should contain one item for each of
the following commands from A1: ‘o’ (add oil slick), ‘f’ (pick up fuel can), and ‘n’ (new colors).
(Give each of these commands appropriate names on the menu).
The “File” menu should contain at least items “New”, “Save”, “Sound”, “About”, and “Quit”.
Only the “Sound”, “About” and “Quit” items need to do anything for this assignment. (Menu
items which do nothing else should at least display a message on the console indicating that
they were invoked). The Sound menu item should include a JCheckBoxMenuItem showing
the current state of the “sound” attribute (in addition to the attribute’s state being shown on the
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ScoreView GUI panel as described below). Selecting the Sound menu item check box should
set a boolean “sound” attribute to “ON” or “OFF”, accordingly.
The “About” menu item is to display a JOptionPane dialog box (see
JOptionPane.showMessageDialog()) giving your name, the course name, and any other
information (for example, the version number of the program) you want to display. “Quit”
should invoke the “quit command” object (the same object invoked by the ‘q’ key binding and
by the “Quit” GUI Button). It should prompt graphically for confirmation and then exit the
program; JOptionPane.showConfirmDialog() can be used for this.
The ScoreView class should extend JPanel and contain JLabel components for each
of the game state values from A1 (time, lives, etc.), plus the new attribute “Sound” with value
either ON or OFF.3
As described above, ScoreView must be registered as an observer of
GameWorld. Whenever any change occurs in GameWorld, the update() method in its
observers is called. In the case of the ScoreView, what update() does is update the
contents of the JLabels displaying the game state values in the JPanel (use JLabel
method setText(String) to update the label). Note that these are exactly the same game
state values as were displayed previously (with the addition of the “Sound” attribute); the only
difference now is that they are displayed graphically in a JLabel.
Although we cover most of the GUI building details in the lecture notes, there will most
likely be some details that you will need to look up using the online Java documentation. It will
become increasingly important that you familiarize yourself with and utilize this resource.
Command & Singleton Design Patterns
Invoking a command should execute a corresponding command object, whether the
command is invoked from a button, a keystroke, or a menu item. Further, it is a requirement
that there be only a single instance of each command object in the program. Said another
way, it is a requirement that commands be implemented using the Singleton and Command
design patterns.
The recommended approach for implementing command classes is to have each
Command extend the Java AbstractAction class, as shown in the course notes. Code to
perform the command operation then goes in the command’s actionPerformed() method.
Java AbstractButton subclasses (for example, JButton and JMenuItem), are
automatically able to be “holders” for such command objects; AbstractButtons have a
setAction() method which allows inserting a command (Action) object into the “command
holder” (button, menu item, etc.). AbstractActions automatically become listeners when
added to an AbstractButton via setAction(), and the specified Action is automatically
invoked when the component is activated (for example, when a button is pressed), so if you
use the Java facilities correctly then this particular observer/observable relationship is taken
care of automatically.
The game initialization code should create a single instance of each command object (for
example, an “accelerate player’s car” command object, a “player’s car entered oil slick”
command object, etc.), then insert the command objects into the appropriate command holders
(control panel buttons, menu items, and/or Key Binding ActionMaps) using methods like
3
In this version of the game there will not actually be any sound; just the state value ON or OFF (a Boolean
attribute that is true or false). We’ll see how to actually add sound later.
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setAction() (for GUI components) or put() (for ActionMaps). Note that some
commands can be invoked in multiple ways (e.g. from a keystroke and from a button); it is a
requirement that only one Command object be implemented for each command and that the
same Command object be invoked from each different Command Holder. As a result, it is
important to make sure that nothing in any command object contains knowledge of how the
command was invoked.
As discussed in class, some command objects may need to be provided with targets. For
example, a command might have the GameWorld as its target if it needs access to game
object data. You could implement the specification of a command’s target either by passing the
target to the command constructor, or by including a “setTarget()” method in the command
and then passing the GameWorld to the command object after it is created.
Iterator Design Pattern
The game object collection in the GameWorld must be accessed through an appropriate
implementation of the Iterator/Collection design pattern. That is, any routine that needs to
process the objects in the collection must not access the collection directly, but must instead
acquire an iterator on the collection and use that iterator to access the objects. You may use
the interfaces discussed in class for this, or the more complex Java versions, or you may
develop your own. Note however the following implementation requirement: the Game Object
collection must provide an iterator completely implemented by you. Even if the data structure
you use has an iterator provided by Java, you must implement an iterator yourself.
Strategy Design Pattern
Non-Player Cars move around the world according to their current strategy. That is, the
NPC move() method uses the current strategy of that car to determine how to move, and the
strategy can be changed on the fly (i.e. while the program is running). You are to implement at
least two different NPC movement strategies: the first strategy causes the NPC to move
directly toward the next pylon (that is, the pylon with a sequence number one higher than the
one it most recently encountered); the second strategy causes the NPC to update its heading
every time it is told to move so that the heading points toward the location of the player’s car
(in other words, its strategy is to play “Destruction Derby” by trying to ram into the player’s car).
You may also implement additional strategies if you like, although this is not required (for
example, you might have a strategy where an NPC simply moves in circles, or a strategy
where it moves back-and-forth between two pylons).
The program must use the Strategy design pattern to define the strategy for each NPC.
When an NPC is created it should be assigned a strategy chosen from among the available
strategies. It is a requirement that NPCs may not all have the same initial strategy; other than
that you may assign initial strategies however you choose. Like all GameObjects, NPCs
should include a toString() method; the NPC toString() should return a string which includes an
identification of that NPC’s current strategy.
When the human player invokes the “switch strategy” command (which happens when
either the space bar or the appropriate GUI button is pressed), the game should cause all
NPCs to switch to a different movement strategy. Switching strategies is to be done by
invoking the strategy Context’s setStrategy() method. You may choose the algorithm which
determines the new NPC strategy, as long as every NPC acquires a new strategy each time
the “switch strategy” command is invoked. Additionally, you should arrange that as a side
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effect of “switching strategies”, each NPC gets a new “highest pylon reached” value
(otherwise, NPCs will never move beyond Pylon #2 since we have no command analogous to
“pxx” which applies to NPCs).
Additional Notes
Recall that there are two approaches which can be used to implement the Observer
pattern: defining your own Observable interface, or extending the Java Observable
class. Because of things we will do later, it will be more complicated if you choose to
extend the Java Observable class; it is recommended that you build your Observable
objects by having them implement a user-defined Observable interface such as the one
described in class, even though it requires implementing the code yourself to keep track of
the list of Observers.
Make your initial GUI frame reasonably large, but small enough to work on most screens (a
size of something like 1000×800 is usually a decent starting point).
Note that all game data manipulation by a command is accomplished by the command
object invoking appropriate methods in the GameWorld (the model). Note also that every
change to the GameWorld will invoke both the MapView and ScoreView observers – and
hence generate the output formerly associated with the ‘d’ and ‘m’ commands. This means
you do not need the ‘d’ or ‘m’ commands; the output formerly produced by those
commands is now generated by the observer/observable process.
Programs must contain appropriate documentation as described in A1 and in class.
Since ‘tick’ causes movable objects to move, every ‘tick’ results in a new map view being
output (because each tick changes the model). However, it is not the responsibility of the
‘tick’ command code to produce this output; it is an effect of the observable/observer
pattern. Note this is not the only command that generates output as a side effect – verify
that your program correctly produces updated views automatically whenever appropriate.
The mechanism for using Java “Key Bindings” is to define a KeyStroke object for each
key and insert that object into the WHEN_IN_FOCUSED_WINDOW input map for the game
world map display panel while also inserting the corresponding Command object into the
panel’s ActionMap. Java KeyStroke objects can be created by calling
KeyStroke.getKeyStroke(), passing it either a single character or else a String
defining the key (string key definitions are exactly the letters following “VK_” in the Virtual
Key definitions in the KeyEvent class). For example:
KeyStroke bKey = KeyStroke.getKeyStroke(“b”);
KeyStroke downArrowKey = KeyStroke.getKeyStroke(“DOWN”);
JComponents such as JButtons automatically apply a key binding for the SPACE key
when they are created. This is what causes the normal Java GUI application behavior
where pressing SPACE automatically invokes the component which has focus. However,
this behavior is detrimental in this kind of program: if you click on a button (to invoke its
action), that button acquires focus; if you then hit the SPACE bar it will automatically invoke
the button again (because the button has focus and contains a key binding for SPACE). To
suppress this behavior, so that hitting SPACE invokes the Action you assign in the
WHEN_IN_FOCUSED_WINDOW input map and not also the action in the button with focus,
you need to remove the button’s default binding for SPACE. To do that, you assign the
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special action name “none” to the button’s input map. That is, for each JButton you
create, you should execute the following statement:
button.getInputMap().put(KeyStroke.getKeyStroke(“SPACE”),”none”);
You may not use a “GUI Builder” tool for this assignment (if you don’t know what a “GUI
Builder” is, don’t worry about it; we’ll be covering it later in the semester).
As before, your program for this assignment must be contained in a single Java package.
The requirements are the same as for the previous assignment, except that this time the
name of the package must be exactly “a2”.
All functionality from the previous assignment must be retained unless it is explicitly
changed or deleted by the requirements for this assignment.
You should develop a UML diagram including not only the major fields and methods
required but also the interfaces and the relationships between classes (for example,
Observer/Observable). This will be particularly useful in helping you understand what
modifications you need to make to your code from A1.
If you wish to use your own “Command” interface structure, rather than the built-in Java
AbstractButton class, you may. However, if you do, you will have to implement the
“Command Holder” facility yourself, and take care of setting up the listener and callback
mechanisms. Using the built-in Java structures is likely to be considerably simpler.
Although the MapView JPanel is empty for this assignment, you should put a border
around it and install it in the frame, to at least make sure that it is there. You may if you
wish also enhance your MapView to include the text output generated by the changes in
the gameworld map; for example, you could add a JTextArea object to the MapView
panel and use method JTextArea.append() to add text to it. However, the map text
must also still appear on the console.
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Sample GUI
The following shows an example of what your game GUI might look like. Notice that it
has the required menus, a control panel on the left containing all the required buttons, a
ScoreView panel near the top showing the current game state information, and an (empty)
bordered MapView panel in the middle for future use. The game title displays at the top. The
user has just hit the “Collide With Pylon” button, displaying the required input dialog.
Deliverables
Submitting your program requires the same three steps as for A1: (1) create a single ZIP
file containing your UML diagram in PDF form, your source code (.java) files, and your
compiled code (.class) files; (2) verify your submission by unzipping your ZIP file to an empty
folder and executing the program using the command java a2.Starter ; and then (3) upload
your ZIP file to SacCT.
Also include in your ZIP a text file called “readme” in which you describe any changes or
additions you made to the assignment specifications (for instance, if you bind any additional
keys or add extra buttons, explain those in your readme file). Also include a description of any
additional strategies in your readme file.
Be sure to keep a backup copy of all submitted work. All submitted work must be strictly
your own.
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Java Notes
Below is one possible organization for your MVC code for A2. Note that this organization is
based on the assumption of using interfaces for both the Observer and the Observable. If you
choose instead to use Java’s Observable class, you will have to modify the code to account for
that. Note also that this pseudocode shows one way of registering Observers with
Observables: having the controller handle the registration. It is also possible to have each
Observer handle its own registration in its constructor (examples are shown in the course
notes). You may use either approach in your program.
public class Game extends JFrame {
private GameWorld gw;
private MapView mv; // new in A2
private ScoreView sv; // new in A2
public Game() {
gw = new GameWorld(); // create “Observable” GameWorld
gw.initLayout(); // initialize world
mv = new MapView(); // create an “Observer” for the map
sv = new ScoreView(); // create an “Observer” for the game state data
gw.addObserver(mv); // register the map Observer
gw.addObserver(sv); // register the score observer
// code here to create menus, create Command objects for each command,
// add commands to Command menu, create a control panel for the buttons,
// add buttons to the control panel, add commands to the buttons, and
// add control panel, MapView panel, and ScoreView panel to the frame
setVisible(true);
}
}
public interface IGameWorld {
//specifications here for all GameWorld methods
}
public class GameWorld implements IObservable, IGameWorld {
// code here to hold and manipulate world objects, handle
// observer registration, invoke observer callbacks, etc.
}
public class GameWorldProxy implements IObservable, IGameWorld {
// code here to accept and hold a GameWorld, provide implementations
// of all the public methods in a GameWorld, forward allowed
// calls to the actual GameWorld, and reject calls to methods
// which the outside should not be able to access in the GameWorld.
}
public class MapView extends JPanel implements IObserver {
public void update (Observable o, Object arg) {
// code here to output current map information (based on
// the data in the Observable) to the console
}
}
public class ScoreView extends JPanel implements IObserver {
public void update (Observable o, Object arg) {
// code here to update JLabels from data in the Observable
}
}
JC:PM / jc
2/26/2015