Class Associations & Interfaces

This semester we will study object-oriented graphics programming and design by
developing a simple video game we’ll call OnTarget. In this game, you (the player) will be
controlling an ant walking around a path while trying to avoid collisions with spiders and keeping
your ant fed.
The goal of this first assignment is to develop a good initial class hierarchy and control
structure by designing the program in UML and then implementing it in Codename One (CN1).
This version will use keyboard input commands to control and display the contents of a “game
world” containing the set of objects in the game. In future assignments, many of the keyboard
commands will be replaced by interactive GUI operations, and we will add graphics, animation,
and sound. For now we will simply simulate the game in “text mode” with user input coming from
the keyboard and “output” being lines of text on the console.
Program Structure
Because you will be working on the same project all semester, it is extremely important
to organize it correctly from the beginning. Pay careful attention to the class structure described
below and make sure your program follows this structure accurately.
The primary class in the program encapsulates the notion of a Game. A game in turn
contains several components, including (1) a GameWorld which holds a collection of game
objects and other state variables, and (2) a play() method to accept and execute user
commands. Later, we will learn that a component such as GameWorld that holds the program’s
data is often called a model.
The top-level Game class also manages the flow of control in the game (such a class is
therefore sometimes called a controller). The controller enforces rules such as what actions a
player may take and what happens as a result. This class accepts input in the form of keyboard
commands from the human player and invokes appropriate methods in the game world to
perform the requested commands – that is, to manipulate data in the game model.
In this first version of the program the top-level Game class will also be responsible for
displaying information about the state of the game. In future assignments, we will learn about a
separate kind of component called a view which will assume that responsibility.
When you create your CN1 project, you should name the main class as Starter. Then
you should modify the start() method of the Starter class so that it would construct an instance
of the Game class. The other methods in Starter (i.e., init(), stop(), destroy()) should not be
altered or deleted. The Game class must extend from the built-in Form class (which lives in
com.codename1.ui package). The Game constructor instantiates a GameWorld, calls a
GameWorld method init() to set the initial state of the game, and then starts the game by
calling a Game method play(). The play()method then accepts keyboard commands from
the player and invokes appropriate methods in GameWorld to manipulate and display the data
and game state values in the game model. Since CN1 does not support getting keyboard input
from command prompt (i.e., the standard input stream,, supported in Java is not
available in CN1) the commands will be entered via a text field added to the form (the Game
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class). Refer to “Appendix – CN1 Notes” for the code that accepts keyboard commands through
the text field located on the form.
The following shows the pseudo-code implied by the above description. It is important for
things that we will do later that your program follows this organization:
class Starter {
//other methods
public void start() {
if(current != null){;
new Game();
//other methods
import com.codename1.ui.Form;
public class Game extends Form{
private GameWorld gw; public
Game() { gw = new
private void play() {
// code here to accept and
// execute user commands that
// operate on the game world
//(refer to “Appendix – CN1
//Notes” for accepting
//keyboard commands via a text
//field located on the form)
public class GameWorld {
public void init(){
//code here to create the
//initial game objects/setup
// additional methods here to
// manipulate world objects and
// related game state data }
Game World Objects
For now, assume that OnTarget game world size is fixed and covers 1000 (width) x 1000
(height) area (although we are going to change this later). The origin of the “world” (location
(0,0)) is the lower left hand corner. The game world contains a collection which aggregates
objects of abstract type GameObject. There are two abstract kinds of game objects called: “fixed
objects” of type Fixed with fixed locations (which are fixed in place) and “moveable objects” of
type Movable with changeable locations (which can move or be moved about the world). For
this first version of the game there are two concrete types that fixed objects are instantiated from
which are called: Flag and FoodStation; and there are two concrete types that moveable
objects are instantiated from which are called: Ant and Spider. Later we may add other kinds
of game objects (both Fixed kinds and Moveable kinds) as well.
The various game objects have attributes (fields) and behaviors (methods) as defined
below. These definitions are requirements which must be properly implemented in your program.
• All game objects have an integer attribute size. All game objects provide the ability for
external code to obtain their size. However, they do not provide the ability to have their size
changed once it is created. As will be specified in the later assignments, each type of game
object has a different shape which can be bounded by a square. The size attribute provides
the length of this bounding square. All flags have the same size (chosen by you), assigned
when they are created (e.g., size of all flags can be 10). You should also assign a size value
to the ant. Sizes of the rest of the game objects are chosen randomly when created, and
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constrained to a reasonable positive integer value (e.g., between 10 to 50). For instance,
size of one of the food stations may be 15 while size of another food station may be 20.
• All game objects have a location, defined by Point built-in class of CN1 (which resides under
com.codename1.charts.models and uses float values), which is constituted from
non-negative X and Y values that initially should be in the range 0.0 to 1000.0 and 0.0 to
1000.0, respectively. The point (X,Y) is the center of the object. Hence, initial locations of all
game objects should always be set to values such that the objects’ centers are contained in
the world. All game objects provide the ability for external code to obtain their location. By
default, game objects provide the ability to have their location changed, unless it is explicitly
stated that a certain type of game object has a location which cannot be changed once it is
created. Except flags and the ant, initial locations of all the game objects should be assigned
randomly when created.
• All game objects have a color, defined by a int value (use static rgb() method of CN1’s
built-in ColorUtil class to generate colors). Initially, all objects of the same class have the
same color (chosen by you), assigned when the object is created (e.g., flags could be blue,
the ant could be red, food stations can be green, spiders can be black). All game objects
provide the ability for external code to obtain their color. By default, game objects provide the
ability to have their color changed, unless it is explicitly stated that a certain type of game
object has a color which cannot be changed once it is created.
• Flags are fixed game objects that have attribute sequenceNumber. Each flag is a numbered
marker that acts as a “waypoint” on the path; following the path is accomplished by walking
over on top of flags in sequential order (the flags mark the course of the path on the ground,
see the diagram below). Flags are not allowed to change color once they are created. All
flags should be assigned to locations chosen by you, when they are created.
• FoodStations are fixed game objects that have an attribute capacity (amount of food a food
station contains). The initial capacity is proportional to the size of the food station. When the
ant is hungry (i.e., running low on its food level), it must walk to a food station that is not
empty before its food level becomes zero; otherwise it cannot move.
• All fixed game objects are not allowed to change location once they are created.
• Moveable game objects have integer attributes heading and speed. Telling a moveable
object to move() causes the object to update its location based on its current heading and
speed. The movable game objects move simultaneously according to their individual speed
and heading. Heading is specified by a compass angle in degrees: 0 means heading north
(upwards on the screen), 90 means heading east (rightward on the screen), etc. See below
for details on updating an movable object’s position when its move() method is invoked.
• Some movable game objects are steerable, meaning that they provide an interface called
ISteerable that allows other objects to change their heading (direction of movement) after
they have been created. Note that the difference between steerable and moveable is that
other objects can request a change in the heading of steerable objects whereas other objects
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can only request that a movable object update its own location according to its current speed
and heading.
• Ant is moveable and steerable game object with attributes maximumSpeed, foodLevel,
foodConsumptionRate, healthLevel, and lastFlagReached.
The maximumSpeed of the ant is the upper limit of its speed attribute; attempts to accelerate
the ant beyond its maximumSpeed are to be ignored (that is, the ant can never go faster than
its maximumSpeed). You should set this value to a reasonable value.
The foodLevel of the ant indicates how hungry it is; if the ant’s food level is zero, it would
have zero speed and cannot move. You should set this value to an initial reasonable value.
The foodConsumptionRate of the ant indicates how much food the ant needs to consume
each time the clock ticks. You should set this value to a reasonable value.
The healthLevel of the ant starts at 10 and decreases each time the ant collides with a spider
(see below for details). Heath level affects the performance of the ant as follows: if the ant
has a perfect health (i.e., has health value 10), it can accelerate all the way up to its
maximumSpeed; if the ant’s health value is zero it would have zero speed and thus, cannot
move at all; and if the ant’s health value is between 10 and zero, it should be limited in speed
to a corresponding percentage of their speed range (e.g., if the ant’s health value is 5, it can
only achieve 50% of its maximum speed). When the ant health is degraded because it is
involved in a collision (see below for details), its speed is reduced (if necessary) so that this
speed-limitation rule is enforced.
The lastFlagReached indicates the sequence number of the last flag that the ant has
reached in the increasing order.
Initially, the ant should be positioned at the location of flag #1 (initially lastFlagReached is
assigned to “1”) and its heading should be assigned to zero and speed should be assigned
to an appropriate positive non-zero value.
• Later we may add other kinds of game objects to the game which are steerable. • Spiders are
moveable (but not steerable) objects which walk on the ground the path is on. They add (or
subtract) small random values (e.g., 5 degrees) to their heading while they move so as to not
run in a straight line. If the spider’s center hits a side of the world, it changes heading and does
not move out of bounds. If the spider gets to the same location as the ant it decreases the health
level of the ant by one. Spiders are not allowed to change color once they are created. Speed of
a spider should be initialized to a reasonable random value (e.g., ranging between 5 and 10) at
the time of instantiation. Heading of a spider should be initialized to a random value (ranging
between 0 and 359) at the time of instantiation.
The preceding paragraphs imply several associations between classes: an inheritance
hierarchy, interfaces such as for steerable objects, and aggregation associations between
objects and where they are held. You are to develop a UML diagram for the relationships, and
then implement it in CN1. Appropriate use of encapsulation, inheritance, aggregation, abstract
classes, and interfaces are important grading criteria. Note that an additional important criterion
is that another programmer must not be able to misuse your classes, e.g., if the object is specified
to have a fixed color, another programmer should not be able to change its color after it is
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You must use a tool to draw your UML (e.g., Violet or any other UML drawing tool) and
output your UML as a pdf file. Make sure to print your UML to a single-page pdf file in the
portrait orientation (it is OK if the fonts and shapes look small on the pdf page since we can
zoom-in to see the details). You are not allowed to use tools that automatically generate a UML
from your code. Your UML must show all important associations between your entities (and builtin classes/interfaces that your entities extend/implement) and utilize correct graphical notations.
For your entities you must use three-box notation (for built-in entities use one-box notation) and
show all the important fields and methods. You must indicate the visibility modifiers of your fields
and methods, but you are not required to show parameters in methods and return types of the
Game Play
When the game starts the player has three “lives” (chances to reach the last flag). The
game has a clock which counts up starting from zero and the objective is to walk around the path
to the last flag in the minimum amount of time.
The player uses keystroke commands to change the ant’s heading (see below for details).
The ant moves by its current speed in the direction it is currently heading each time the game
clock “ticks” (see below).
The ant starts out at the first flag (#1). The player must walk the ant so that it intersects
the flags in increasing numerical order. Each time the ant reaches the next higher-numbered
flag the ant is deemed to have successfully walk that far along the path and its lastFlagReached
field is updated. Intersecting flags out of order (that is, reaching a flag whose number is more
than one greater than the most recently reached flag, or whose number is less than or equal to
the most recently reached flag) has no effect on the game.
The food level of the ant continually goes down as the game continues. If the ant’s food
level reaches zero it can no longer move. The player must therefore occasionally walk the ant
off the path to intersect with a food station, which has the effect of increasing the ant’s food level
by the capacity of the food station. After the ant intersects with the food station, the capacity of
that food station is reduced to zero and a new food station with randomly-specified size and
location is added into the game.
Collisions with spiders decrease the health level of the ant by one; if the health level of
the ant reaches zero, it can no longer move.
If the ant can no longer move (i.e., its food or health level has reached zero), the game
stops (the player “loses a life”) and the game world is re-initialized (but the number of clock ticks
is not set back to zero). When the player loses all three lives the game ends and the program
exits by printing the following text message in console: “Game over, you failed!”. If the ant
reaches the last flag on the path, the game also ends with the following message displayed on
the console: “Game over, you win! Total time: #”, where # indicates the number of clock ticks it
took the ant to reach the last flag on the path.
The program keeps track of following “game state” values: current clock time and lives
remaining. Note that these values are part of the model and therefore belong in the GameWorld
Once the game world has been created and initialized, the Game constructor is to call a
method name play() to actually begin the game. play() accepts single-character commands
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from the player via the text field located on the form (the Game class) as indicated in the
“Appendix – C1 Notes”.
Any undefined or illegal input should generate an appropriate error message on the
console and ignore the input. Single keystrokes invoke action — the human hits “enter” after
typing each command. The allowable input commands and their meanings are defined below
(note that commands are case sensitive):
• ‘a’ – tell the game world to accelerate (increase the speed of) the ant by a small amount.
Note that the effect of acceleration is to be limited based on health level, food level, and
maximum speed as described above.
• ‘b’ – tell the game world to brake (reduce the speed of) the ant by a small amount. Note that
the minimum speed for the ant is zero.
• ‘l’ (the letter “ell”) – tell the game world to change the heading of the ant by 5 degrees to the
left (in the negative direction on the compass).
• ‘r’ – tell the game world to change the heading of the ant by 5 degrees to the right (in the
positive direction on the compass).
• ‘a number between 1-9’– PRETEND that the ant has collided with (walked over) the flag
number x (which must have a value between 1-9); tell the game world that this collision has
occurred. The effect of walking over a flag is to check to see whether the number x is exactly
one greater than the flag indicated by lastFlagReached field of the ant and if so, update the
lastFlagReached field of the ant by increasing it by one.
• ‘f’ – PRETEND that the ant has collided with a food station; tell the game world that this
collision has occurred. The effect of colliding with a food station is to increase the ant’s food
level by the capacity of the food station (in this version of the assignment, pick a non-empty
food station randomly), reduce the capacity of the food station to zero, fade the color of the
food station (e.g., change it to light green), and add a new food station with randomlyspecified size and location into the game.
• ‘g’ – PRETEND that a spider has gotten to the same location and collided with the ant. The
effect of colliding with a spider is to decrease the health level of the ant as described above,
fade the color of the ant (i.e., it becomes lighter red – throughout the game, the ant can have
different shades of red), and (if necessary) reduce the speed of the ant so that abovementioned speed-limitation rule is enforced. Since currently no change is introduced to the
spider after the collision, it does not matter which spider is picked.
• ‘t’ – tell the game world that the “game clock” has ticked. A clock tick in the game world has
the following effects: (1) Spiders update their heading as indicated above. (2) all moveable
objects are told to update their positions according to their current heading and speed, and
(3) the ant’s food level is reduced by the amount indicated by its foodConsumptionRate, (4)
the elapsed time “game clock” is incremented by one (the
game clock for this assignment is simply a variable which increments by one with each
tick). Note that all commands take immediate effect and not depend on ‘t’ command (e.g.,
if ‘a’ is hit, the ant’s speed value would be increased right away without waiting for the
next ‘t’ command to be entered).
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• ‘d’ – generate a display by outputting lines of text on the console describing the current
game/ant state values. The display should include (1) the number of lives left, (2) the current
clock value (elapsed time), (3) the highest flag number the ant has reached sequentially so
far (i.e., lastFlagReached), (4) the ant’s current food level (i.e., foodLevel), and (5) the ant’s
health level (i.e., healthLevel). All output should be appropriately labeled in easily readable
• ‘m’ – tell the game world to output a “map” showing the current world (see below).
• ‘x’– exit, by calling the method System.exit(0) to terminate the program. Your program
should confirm the user’s intent to quit before actually exiting. This means your program
should force the user to enter ‘y’ or ‘n’ (see ‘y’ and ‘n’ commands below) to the text field (and
hit enter) after (s)he enters ‘x’ to the text field (and hits enter). To accomplish this, consider
setting a flag in your code whenever the last entered command from the text field is ‘x’. Then,
if the last entered command is ‘x’ and the user does not say ‘y’ or ‘n’ after saying ‘x’, you can
print a message to the console asking for one of these commands and do not accept any
other commands.
• ‘y’ – user has confirmed the exit by saying yes.
• ‘n’ – user has not confirmed the exit by saying no.
Some of commands above indicate that you PRETEND a collision happens. Later this
semester, your program will determine these collisions automatically1
The code to perform each command must be put in a separate method. When the Game
gets a command which requires manipulating the GameWorld, the Game must invoke a method
in the GameWorld to perform the manipulation (in other words, it is not appropriate for the Game
class to be directly manipulating objects in the GameWorld; it must do so by calling an
appropriate GameWorld method). The methods in GameWorld, might in turn call other methods
that belong to other classes.
When the player enters any of the above commands, an appropriate message should be
displayed in console (e.g., after ‘b’ is entered, print to console something like “break is applied”).
Additional Details
• Method init() is responsible for creating the initial state of the world. This should include
adding to the game world at least the following: a minimum of four Flag objects, positioned
and sized as you choose and numbered sequentially defining the path (you may add more
than four initial flags if you like – maximum number of flags you can add is nine); one Ant,
initially positioned at the flag #1 with initial heading which is zero, initial positive non-zero
speed as you choose, and initial size as you choose; at least two Spider objects, randomly
positioned with a randomly-generated size, heading, and speed; and at least two FoodStation
objects with random locations and with random sizes.
In later assignments we will see how to actually detect on-screen collisions such as this; for now we are simply
relying on the user to tell the program via a command when collisions have occurred. Inputting a collision
command is deemed to be a statement that the collision occurred; it does not matter where objects involved
in the collision actually happen to be for this version of the game as long as they exist in the game.
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• All object initial attributes, including those whose values are not otherwise explicitly specified
above, should be assigned such that all aspects of the gameplay can be easily tested (e.g.,
spiders should not move so fast that it is impossible for them to ever cause a harm to the
• In this first version of the game, it is possible that some of the abstract classes might not
include any abstract methods (or some classes might not have any fields/methods). In future
assignments, we may add such class members as needed.
• In order to let a child class set a private field defined in its parent that does not provide a
proper public setter for the field, consider having a constructor in the parent that takes in the
value to be set as a parameter (e.g., public MyParentClass(int i) {myField =
i;…}) and calling this constructor from the child’s constructor (e.g., public
MyChildClass(int value) {super(value);…}, note that the value is passed as a
parameter to child constructor instead of being generated there). If the field resides in the
parent of the parent class, consider having the proper constructor in that class (e.g. public
MyGrandParentClass(int i) {myField = i;…}) and calling it from the constructor
of the parent class (e.g., public MyParentClass(int i)
{super(i);…}) to pass the value coming from the child to the grandparent.
• If a setter is defined in a parent class and you want to prevent the child to have an ability to
set that value, consider overriding the setter in the child with the method that has empty body
implementation (e.g., public void setX(int i){})
• All classes must be designed and implemented following the guidelines discussed in class,
o All data fields must be private. o Accessors / mutators must be provided, but only
where the design requires them.
• Moving objects need to determine their new location when their move() method is invoked,
at each time tick. The new location can be computed as follows:
newLocation(x,y) = oldLocation(x,y) + (deltaX, deltaY), where
deltaX = cos(θ)speed, deltaY = sin(θ)speed,
and where θ = 90 ˗ heading (90 minus the heading). Below diagram shows the derivation of
these calculations for an arbitrary amount of time; in this assignment we are assuming “time”
is fixed at one unit per “tick”, so “elapsed time” is 1 second (1000 milliseconds):
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You can use methods of the built-in CN1 Math class (e.g., Math.cos(), Math.sin()) to
implement the above-listed calculations in move() method. Be aware that these methods
expect the angles to be provided in “radians” not “degrees”. You can use
Math.toRadians() to convert degrees to radians.
• For this assignment all output will be in text form on the console; no “graphical” output is
required. The “map” (generated by the ‘m’ command) will simply be a set of lines describing
the objects currently in the world, as the following:
Flag: loc=200.0,200.0 color=[0,0,255] size=10 seqNum=1
Flag: loc=200.0,800.0 color=[0,0,255] size=10 seqNum=2
Flag: loc=700.0,800.0 color=[0,0,255] size=10 seqNum=3
Flag: loc=900.0,400.0 color=[0,0,255] size=10 seqNum=4
Ant: loc=180.2,450.3 color=[255,0,0] heading=355 speed=50 size=40
maxSpeed=50 foodConsumptionRate=2
Spider: loc=70.3,70.7 color=[0,0,0] heading=45 speed=5 size=25
Spider: loc=950.6,950.3 color=[0,0,0] heading=225 speed=10 size=20
FoodStation: loc=350.8,350.6 color=[0,255,0] size=15 capacity=15
FoodStation: loc=900.0,700.4 color=[0,255,0] size=20 capacity=20
Note that the appropriate mechanism for implementing this output is to override the
toString() method in each concrete game object class so that it returns a String
describing itself (see the “Appendix – CN1 Notes” below). Please see “Appendix – CN1
Notes” below for also tips on how to print one digit after a decimal point in CN1.
For this assignment, the only required depiction of the world is the text output map as
shown above. Later we will learn how to draw a graphical depiction of the world, which
then for the above map might look something like the image shown below (the pictures
in the image are not all precisely to scale, and note that this is only to give you an idea of
what the above map represents – your program is not required to produce any graphical
output like this in the later assignments).
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• You are not required to use any particular data structure to store the game world objects.
However, your program must be able to handle changeable numbers of objects at runtime;
this means you can’t use a fixed-size array, and you can’t use individual variables. Consider
either the Java ArrayList or Vector class for implementing this storage. Note that your storage
will hold elements of type GameObject, but you will need to be able to treat them differently
depending on the type of object. You can use the “instanceof” operator to determine the
type of a given object, but be sure to use it in a polymorphically-safe way. For example, you
can write a loop which runs through all the elements of theWorldVector and processes each
“movable” object with code like:
for (int i=0; i<theWorldVector.size(); i++) {
if (theWorldVector.elementAt(i) instanceof Movable) {
Movable mObj = (Movable)theWorldVector.elementAt(i);
• You can utilize java.util.Random class (see the “Appendix – CN1 Notes” below) to
generate random values specified in the requirements (e.g., to generate initial random sizes
and locations of objects or to pick an object randomly for “pretend” commands).
• It is a requirement for all programs in this class that the source code contain documentation,
in the form of comments explaining what the program is doing, including comments
describing the purpose and organization of each class and comments outlining each of the
main steps in the code. Points will be deducted for poorly or incompletely documented
programs. Use of JavaDoc-style comments is highly encouraged.
• It is a requirement to follow standard Java coding conventions:
o class names always start with an upper case letter,
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o variable names always start with a lower case letter,
o compound parts of compound names are capitalized (e.g., myExampleVariable), o
Java interface names should start with the letter “I” (e.g., ISteerable).
• Your program must be contained in a CN1 project called A1Prj. You must create your project
following the instructions given at “2 – Introduction to Mobile App Development and CN1”
lecture notes posted at Canvas (Steps for Eclipse: 1) File → New → Project →
Codename One Project. 2) Give a project name “A1Prj” and uncheck “Java 8 project” 3) Hit
“Next”. 4) Give a main class name “Starter”, package name “com.mycompany.a1”, and
select a “native” theme, and “Hello World(Bare Bones)” template (for manual GUI building).
5) Hit “Finish”.). Further, you must verify that your program works properly from the
command prompt before submitting it to Canvas: First make sure that the A1Prj.jar file is
up-to-date. Then get into the A1Prj directory and type (all in one line) the following for
Windows machines:
java -cp dist\A1Prj.jar;JavaSE.jar com.codename1.impl.javase.Simulator
For the command line arguments of Mac OS/Linux machines please refer to the class
notes. Penalties will be applied to submissions which do not work properly from the
command prompt.
There are three steps which are required for submitting your program, as follows:

  1. Create a “TEXT” (i.e., not a pdf, doc etc.) file called “readme-a1.txt” that includes the lab
    number and the name of the specific machine you have used in that lab to build/test your
    program. Be sure to verify that your program works from the command prompt on the lab
    machine as explained above. For instructions on how to connect to a lab machine, please see
    the related page on Canvas and for hints on how to build/test your assignment on a lab machine,
    please see the syllabus. In addition, be sure that you include the src folder and jar file
    generated/tested on the lab machine in the below-mentioned zip file. You may also include
    additional information you want to share with the grader in this text file. You will receive the
    grader comments on your text file when grades are posted (click on “View Feedback” link next
    to readme-a1.txt on Canvas to see the comments).
  2. Create a “ZIP” file containing (1) your UML diagram in .PDF format, (2) the entire “src”
    directory under your CN1 project directory (called A1Prj) which includes source code (“.java”)
    for all the classes in your program, and (3) the A1Prj.jar (located under the “A1Prj/dist” directory)
    which is automatically generated by CN1 and includes the compiled (“.class”) files for your
    program in a zipped format. Do NOT include other directories/files under the CN1 project
    directory. Be sure to name your ZIP file as
  3. Login to Canvas, select “Assignment#1”, and upload your TEXT file and ZIP file
    separately (do NOT place this TEXT file inside the ZIP file). Also, be sure to take note of the
    requirement stated in the course syllabus for keeping a backup copy of all submitted work (save
    a copy of your TEXT and ZIP files).
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    All submitted work must be strictly your own!
    Appendix – CN1 Notes
    Input Commands
    In CN1, since is not supported, we will use a text field located on the form
    (i.e. the Game class) to enter keyboard commands. The play() method of Game will look like
    this (we will discuss the details of the GUI and event-handling concepts used in the below code
    later in the semester):
    import com.codename1.ui.Label; import
    com.codename1.ui.TextField; import; import
    private void play()
    Label myLabel=new Label(“Enter a Command:”);
    final TextField myTextField=new TextField();
    myTextField.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent evt) { String sCommand=myTextField.getText().toString();
    if(sCommand.length() != 0)
    switch (sCommand.charAt(0)) {
    case ‘a’:
    //add code to handle rest of the commands
    } //switch
    } //actionPerformed
    } //new ActionListener()
    ); //addActionListener
    } //play
    Random Number Generation
    The class used to create random numbers in CN1 is java.util.Random. This class
    contains several methods including nextInt(), which returns a random integer from the entire
    range of integers, nextInt(int), which returns a random number between zero (inclusive) and
    the specified integer parameter (exclusive), and nextFloat(), which returns float value
    (between 0.0 and 1.0). For instance, if you like to generate a random integer value between X
    and X+Y, you can call X + nextInt(Y).
    13 of 13
    Output Strings
    The routine System.out.println() can be used to display text. It accepts a parameter
    of type String, which can be concatenated from several strings using the “+” operator. If you
    include a variable which is not a String, it will convert it to a String by invoking its toString()
    method. For example, the following statements print out “The value of I is 3”:
    int i = 3 ;
    System.out.println (“The value of I is ” + i);
    Every CN1 class provides a toString() method inherited from Object. Sometimes the
    result is descriptive. However, if the toString() method inherited from Object isn’t very
    descriptive, your own classes should override toString() and provide their own String descriptions
    – including the toString() output provided by the parent class if that class was also implemented
    by you.
    For example, suppose there is a class Book, and a subclass of Book named
    ColoredBook with attribute myColor of type int. An appropriate toString() method in
    ColoredBook might return a description of a colored book as follows:
    public String toString() {
    String parentDesc = super.toString();
    String myDesc = “color: ” + “[” + + “,”
  • + “,”
  • + “]”;
    return parentDesc + myDesc ;
    (Abovementioned static methods of the ColorUtil class return the red, green, and blue
    components of a given integer value that represents a color.)
    A program containing a ColoredBook called “myBook” could then display it as follows:
    System.out.println (“myBook = ” + myBook.toString()); or
    System.out.println (“myBook = ” + myBook);

Sample Solution