Introduction

This semester we will study object-oriented graphics programming and design by developing a simple video game well call Robo-Track. In this game you will be controlling a robot moving on a track defined by bases, while trying to avoid collisions with drones and other robots and keeping your robot charged with energy.

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 screen.

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 programs 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 build-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, System.in, supported in Java is not available in CN1) the commands will be entered via a text field added to the form (the Game 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){ current.show(); return; } new Game(); } //other methods }	import com.codename1.ui.Form; public class Game extends Form{ private GameWorld gw; public Game() { gw = new GameWorld(); gw.init(); play(); } 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 the game world size is fixed and covers 1024(width) x 768(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 kinds of abstract 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: Base and EnergyStation; and there are two concrete types that moveable objects are instantiated from which are called: Robot and Drone. 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 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 bases and all robots have the same size (chosen by you), assigned when they are created (e.g, size of all bases can be 10 and size of all robots can be 40). Sizes of the rest of the game objects are chosen randomly when created, and constrained to a reasonable positive integer value (e.g., between 10 to 50). For instance, size of one of the energy station may be 15 while size of energy station can may be 20.
• All game objects have a location, defined by floating point (you can use float or double to represent it) non-negative values X and Y which initially should be in the range 0.0 to 1024.0 and 0.0 to 768.0, 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 bases and robots, 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 CN1s built-in ColorUtil class to generate colors). All objects of the same class have the same color (chosen by you), assigned when the object is created (e.g, bases could be blue, robots could be red, energy stations can be green). 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.
• Bases are fixed game objects that have attribute sequenceNumber. Each base is a numbered marker that acts as a waypoint on the track; following the track is accomplished by moving over the top of bases in sequential order. Bases are not allowed to change color once they are created. All bases should be assigned to locations chosen by you, when they are created.
• Energy stations are fixed game objects that have an attribute capacity (amount of energy an energy station contains). The initial capacity of the energy station is proportional to its size. If the player robot is running low on energy, it must go to an energy station that is not empty before it runs out of energy; 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 all move the same way and they 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 objects position when its move() method is invoked.
• Some movable game objects are steerable, meaning that they implement 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 can only request that a movable object update its own location according to its current speed and heading.
• Robots are moveable and steerable game objects with attributes steeringDirection, maximumSpeed, energyLevel, energyConsumptionRate, damageLevel, and lastBaseReached.

The steeringDirection of a robot indicates how the steering wheel is turned in relation to the front of the robot. That is, the steering direction of a robot indicates the change the player would like to apply to the heading along which the robot is moving (the steering direction actually gets applied to the heading when the clock ticks given that the robot moves, e.g., the robot did not run out of energy or does not have the maximum damage or zero speed). The steering mechanism in a robot is such that the steering direction can only be changed in units of 5 degrees at a time, and only up to a maximum of 40 degrees left or right of straight ahead (attempts to steer a robot beyond this limit are to be ignored).

The maximumSpeed of a robot is the upper limit of its speed attribute; attempts to accelerate a robot beyond its maximumSpeed are to be ignored (that is, a robot can never go faster than its maximumSpeed). Note that different robots may have different maximumSpeed values, although initially they all start out with zero speed value.

The energyLevel of a robot indicates how much energy it has left; robots with no energy would have zero speed and cannot move. You should set this value to the same initial reasonable value for all robots.

The energyConsumptionRate of a robot indicates how much energy the robot would spend each time the clock ticks. You should set this value to the same reasonable value for all robots.

The damageLevel of a robot starts at zero and increases each time the robot collides with another robot or a drone (see below). The program should define an upper limit on the damage a robot can sustain. Damage level affects the performance of a robot as follows: a robot with zero damage can accelerate all the way up to its maximumSpeed; robots with the maximum amount of damage would have zero speed and thus, cannot move at all; and robots with damage between zero and the maximum damage should be limited in speed to a corresponding percentage of their speed range (for example, a robot with 50% of the maximum damage level can only achieve 50% of its maximum speed). When a robot incurs damage because it is involved in a collision (see below), its speed is reduced (if necessary) so that this speed-limitation rule is enforced.

The lastBaseReached of a robot indicates the sequence number of the last base that the robot has reached in the increasing order.

Initially, the player robot should be positioned at the location of base #1 (initially lastBaseReached is assigned to 1) and its heading and steering direction 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.
• Drones are moveable (but not steerable) objects which fly over the track. 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 drones center hits a side of the world, it changes heading and does not move out of bounds. If a drone flies directly over a robot it causes damage to the robot; the damage caused by a drone is half the damage caused by colliding with another robot but otherwise affects the performance of the robot in the same way as described above. Drones are not allowed to change color once they are created. Speed of drones should be initialized to a reasonable random value (e.g., ranging between 5 and 10) at the time of instantiation. Heading of drones 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 fix color, another programmer should not be able to change its color after it is instantiated.

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 (e.g., print your UML to a pdf file). Your UML must show all important associations between your entities (and important built-in classes that your entities have associations with) and utilize correct graphical notations. For your entities you must use three-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 methods.

Game Play

When the game starts the player has three lives (chances to reach the last base). The game has a clock which counts up starting from zero; in this first version of the game the objective is to have the player robot complete the track (which starts from the first base and ends at the last base) in the minimum amount of time. Currently, there is only one robot (the player robot) in the game. Later we will add other robots (non-player robots) and the objective will also include completing the track before the other robots do.

The player uses keystroke commands to turn the robots steering wheel; this can cause the robots heading to change (turning the steering wheel only effects the robots heading under certain conditions; see above). The robot moves one unit at its current speed in the direction it is currently heading each time the game clock ticks (see below).

The robot starts out at the first base (#1). The player must move the robot so that it intersects the bases in increasing numerical order. Each time the robot reaches the next higher-numbered base, the robot is deemed to have successfully moved that far along the track and its lastBaseReached field is updated. Intersecting bases out of order (that is, reaching a base whose number is more than one greater than the most recently reached base, or whose number is less than or equal to the most recently reached base) has no effect on the game.

The energy level of the robot continually goes down as the game continues (energy level goes down even if the robot has zero speed since the electronics on the robot is continually working). If the robots energy level reaches zero it can no longer move. The player must therefore occasionally move the robot off the track to go to (intersect with) an energy station, which has the effect of increasing the robots energy level by the capacity of the energy station. After the robot intersects with the energy station, the capacity of that energy station is reduced to zero and a new energy station with randomly-specified size and location is added into the game.

Collisions with other robots or with drones cause damage to the robot; if the robot sustains too much damage it can no longer move. If the robot can no longer move (i.e., due to having maximum damage or no energy), 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 player robot reaches the last base on the track, 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 player robot to reach the last flag on the track since the start of the game. In later versions of the game, if a non-player robot reaches the last base before the player does, the game will also end with the following message displayed on the console: Game over, a non-player robot wins!.

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 class.

Commands

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 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 (immediately increase the speed of) the player robot by a small amount. Note that the effect of acceleration is to be limited based on damage level, energy level, and maximum speed as described above.
• b tell the game world to brake (immediately reduce the speed of) the player robot by a small amount. Note that the minimum speed for a robot is zero.
• l (the letter ell) tell the game world to change the steering direction of the player robot by 5 degrees to the left (in the negative direction on the compass). Note that this changes the direction of the robots steering wheel; it does not directly (immediately) affect the robots heading. See the tick command, below.
• r tell the game world to change the steering direction of the player robot by 5 degrees to the right (in the positive direction on the compass). As above, this changes the direction of the robots steering wheel, not the robots heading.
• c PRETEND that the player robot has collided with some other robot; tell the game world that this collision has occurred. (For this version of the program we wont actually have any other robot in the simulation, but we need to provide for testing the effect of such collisions.) Colliding with another robot increases the damage level of the player robot and fades the color of the robot (i.e., the robot color becomes lighter red throughout the game, the robot will have different shades of red); if the damage results in the player robot not being able to move then the game stops (the player loses a life).

a number between 1-9 PRETEND that the player robot has collided with the base number x (which must have a value between 1-9); tell the game world that this collision has occurred. The effect of moving over a base is to check to see whether the number x is exactly one greater than the base indicated by lastBaseReached field of the robot and if so to record in the robot the fact that the robot has now reached the next sequential base on the track (update the lastBaseReached field of the robot).

• e PRETEND that the player robot has collided with (intersected with) an energy station; tell the game world that this collision has occurred. The effect of colliding an energy station is to increase the robots energy level by the capacity of the energy station, reduce the capacity of the energy station to zero, fade the color of the energy station (e.g., change it to light green), and add a new energy station with randomly-specified size and location into the game.
• g PRETEND that a drone has flown over (collided with, gummed up) the player robot. The effect of colliding with a drone is to increase the damage to the robot as described above under the description of drones and fades the color of the robot (i.e., the robot color becomes lighter red).
• t tell the game world that the game clock has t A clock tick in the game world has the following effects: (1) if the player robot moves (e.g., did not run out of energy or does not have the maximum damage or zero speed), then the robots heading should be incremented or decremented by the robots steeringDirection (that is, the steering wheel turns the robot) (2) Drones also update their heading as indicated above. (3) all moveable objects are told to update their positions according to their current heading and speed, and (4) the robots energy level is reduced by the amount indicated by its energyConsumptionRate. (5) the elapsed time game clock is incremented by one (the game clock for this assignment is simply a variable which increments with each tick).
• d generate a display by outputting lines of text on the console describing the current game/player-robot state values. The display should include (1) the number of lives left, (2) the current clock value (elapsed time), (3) the highest base number the robot has reached sequentially so far, (4) the robots current energy level and (5) robots current damage level. All output should be appropriately labeled in easily readable format.
• m tell the game world to output a map showing the current world (see below).
• x exit, by calling the method exit(0) to terminate the program. Your program should confirm the users intent (see y and n commands below) to quit before actually exiting.
• y user has confirmed the exit by saying y
• n user has not confirmed the exit by saying n

Some of commands above indicate that you PRETEND a collision happens. Later this semester, your program will determine these collisions automatically^[1].

The code to perform each command must be encapsulated 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 breaks are applied).

Additional Details

• The program you are to write is an example of what is called a discrete simulation. In such a program there are two basic notions: the ability to change the simulation state, and the ability to advance simulation time. Changing the state of the simulation has no effect (other than to change the specified values) until the simulation time is advanced. For example, entering commands to change the robots steering direction will not actually take effect (that is, will not change the robots heading) until you enter a tick command to advance the time. On the other hand, entering a map command after changing the values will show the new values even before a tick is entered. You should verify that your program operates like this.
• 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 Base objects, positioned and sized as you choose and numbered sequentially defining the track (you may add more than four initial bases if you like maximum number of bases you can add is nine); one Robot, initially positioned at the base #1 with initial heading, steering direction, of zero, initial positive non-zero speed, and initial size as you choose; at least two Drone objects, randomly positioned with a randomly-generated heading and a speed; and at least two EnergyStation objects with random location and with random sizes.
• 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 (for example, drones should not fly so fast that it is impossible for them to ever cause damage to a robot).
• 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 have fields/methods). Later, we might add such class members to meet the new requirements.
• 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 (public MyParentClass(int i) {myField = i;}) and calling this constructor from the childs constructor after generating the value (e.g., public MyChildClass() {;super(value);}). Note that the value could be 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, including:

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()*speed, deltaY = sin()*speed,

and where = 90 heading (90 minus the heading). There is a diagram in course notes (look for the slide title Computed Animated Location (cont.) in the Introduction to Animation chapter) showing 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.

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, similar to the following:

Base: loc=200.0,200.0 color=[0,0,255] size=10 seqNum=1

Base: loc=200.0,800.0 color=[0,0,255] size=10 seqNum=2

Base: loc=700.0,800.0 color=[0,0,255] size=10 seqNum=3

Base: loc=900.0,400.0 color=[0,0,255] size=10 seqNum=4

Robot: loc=180.2,450.3 color=[255,0,0] heading=355 speed=50 size=40 maxSpeed=50 steeringDirection=5 energyLevel=5 damageLevel=2

Drone: loc=70.3,70.7 color=[255,0,255] heading=45 speed=5 size=25

Drone: loc=950.6,950.3 color=[255,0,255] heading=225 speed=10 size=20

EnergyStation: loc=350.8,350.6 color=[0,255,0] size=15 capacity=15

EnergyStation: loc=900.0,700.4 color=[0,255,0] size=20 capacity=20

Note that the above map describes the game shortly after it has started; the robot has moved northward from its initial position at base #1, the robot is traveling at its maximum speed, the player is trying to apply a 5-degree right turn, and so forth. Note also 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 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 a map may represent your program is not required to produce any graphical output like this).

• 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 cant use a fixed-size array, and you cant use individual variables. Consider either the Java ArrayList or Vector class for implementing this storage. Note that Java Vectors (and ArrayLists) hold elements of type Object, but you will need to be able to treat the Objects 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 a world Vector 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); mObj.move();

}

}

• You can utilize 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).
• 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:

• class names always start with an upper case letter, o variable names always start with a lower case letter,
• 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 SacCT (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 SacCT: First make sure that the A1Prj.jar file is up-to-date. If not, under eclipse, right click on the dist directory and say Refresh. Then get into the A1Prj directory and type (all in one line): java -cp distA1Prj.jar;JavaSE.jar com.codename1.impl.javase.Simulator com.mycompany.a1.Starter for Windows machines (for the command line arguments of Mac OS/Linux machines please refer to the class notes). Substantial penalties will be applied to submissions which do not work properly from the command prompt.

Deliverables

There are four steps which are required for submitting your program, as follows:

1. Be sure to verify that your program works from the command prompt as explained above.
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 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. Be sure to name your ZIP file as YourLastName-YourFirstName-a1.zip.
3. Create a TEXT (i.e., not a pdf, doc etc.) file called readme.txt that indicates the system info you have used to generate the .jar file (under dist dir) and test your assignment. List OS, Java, Eclipse, and CN1 versions of your personal machine or list the lab number and machine name if you have used a lab machine. 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.
4. Login to Canvas, select Assignment#1, and upload your ZIP file and TEXT 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 ZIP and TEXT files).

All submitted work must be strictly your own!

Appendix CN1 Notes

Input Commands

In CN1, since System.in 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.events.ActionListener; import com.codename1.ui.Label; import com.codename1.ui.TextField; import com.codename1.ui.events.ActionEvent; import java.lang.String;

private void play()

{

Label myLabel=new Label(Enter a Command:); this.addComponent(myLabel);

final TextField myTextField=new TextField(); this.addComponent(myTextField);

this.show();

myTextField.addActionListener(new ActionListener(){

public void actionPerformed(ActionEvent evt) {

String sCommand=myTextField.getText().toString();

myTextField.clear();

switch (sCommand.charAt(0)) { case x: gw.exit();

break;

//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).

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 isnt 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: + [ + ColorUtil.red(myColor) + ,

+ ColorUtil.green(myColor) + ,

+ ColorUtil.blue(myColor) + ];

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 simply:

System.out.println (myBook = + myBook);

Number Formatting

The System.out.format() and String.format() methods supported in Java are not available in CN1. Hence, in order to display only one digit after the decimal point you can use Math.round() function:

double dVal = 100/3.0;

double rdVal = Math.round(dVal*10.0)/10.0; System.out.println(original value: + dVal); System.out.println(rounded value: + rdVal);

Above prints the following to the standard output stream:

original value: 33.333333333333336 rounded value: 33.3

[1] 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.