CS300 P04 Carrot Patch solution




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This assignment involves the development of a graphic application from the scratch. This will
give you practice with implementing interfaces, and defining an hierarchy of classes including
super classes, and subclasses. We’ll also work on improving the organization and clarity of your
code. Having this programming assignment as reference, you will also be able to develop your
own graphical application using the processing library, from the scratch. We no longer need
to use the Utility class provided for you in the p2core.jar file in P2. The CarrotPatch graphic
application defines different graphic components which can be drawn to the display window.
We distinguish:
• Carrots which are non interactive images. They do not react to the mouse events or to
key pressed by the user.
• Interactive objects such as buttons and animals (rabbits and wolves). These graphic
objects are GUI listeners objects which react to the mouse events or specific key pressed.
They define common properties and common behaviors. But they act differently in the
patch. Each animal/button has a specific behavior indeed. We are going to define and
implement these similarities and differences in this assignment.
A screenshot of what the display window of this Carrot Patch application may look like after
you have completed this assignment is shown in Fig.1. A demo of this application is provided
soon in this video.
Learning Objectives
The goals of this assignment include:
• Experience organizing code in an object oriented fashion that takes advantage of inheritance
relationships between your classes.
• Use of inheritance and interfaces to better organize your code in a more clear and concise
manner. Students will also enjoy the power of polymorphism.
• Learn how to use PApplet class defined in the processing graphic library directly to
develop a graphic application from the scratch, rather than through a provide .jar wrapper
• Gain experience with writing tests to assess the correctness of your program. All developed
test methods will be run with graphic mode disabled and would assert the correctness of
specific methods in your code.
©2021 Kacem & LeGault – University of Wisconsin – Madison.
Figure 1: Carrot Patch Graphic User Interface
Grading Rubric
5 points Pre-Assignment Quiz: The P4 pre-assignment quiz is accessible through
Canvas before having access to this specification by 11:59PM on Sunday
02/28/2021. Access to the pre-assignment quiz will be unavailable passing
its deadline.
20 points Immediate Automated Tests: Upon submission of your assignment
to Gradescope, you will receive feedback from automated grading tests
about whether specific parts of your submission conform to this write-up
specification. If these tests detect problems in your code, they will attempt to
give you some feedback about the kind of defect that they noticed. Note that
passing all of these tests does NOT mean your program is otherwise correct.
To become more confident of this, you should run additional tests of your own.
25 points Additional Automated Tests: When your manual grading feedback
appears on Gradescope, you will also see the feedback from these additional
automated grading tests. These tests are similar to the Immediate Automated
Tests, but may test different parts of your submission in different ways.
Additional Assignment Requirements and Notes
• The only import statements that you may include in your project’s classes are:
import java.io.File;
import java.util.ArrayList;
import java.util.Random;
import processing.core.PApplet;
import processing.core.PImage;
• The automated grading tests in gradescope are NOT using the full processing library
when grading your code. These tests only know about the following fields and methods
(referenced directly from this assignment). If you are using any other fields, methods, or
classes from the processing library, this will cause problems for the automated grading
tests. Such references must be replaced with references to one or more of the following:
– PImage: the two fields int width, and int height.
– PApplet: the three fields int mouseX, int mouseY, and boolean mousePressed.
– Five methods from PApplet: PImage loadImage(String), void image(PImage,int,int),
void size(int,int), void getSurface().setTitle(String), and void main(String).
• You are NOT allowed to add any constant or variable not defined or provided in this
write-up outside of any method.
• You are NOT allowed to add any public method (static or instance) not defined in this
• Overriding a method does not mean adding a new public method not defined in the
write-up. Feel free to override any public behavior implemented in a superclass, if needed.
• You CAN define local variables that you may need to implement the methods defined in
this program.
• You CAN define private static methods to help implement the different public methods
defined in this write-up, if needed.
• Do NOT submit the following source files to gradescope: ListenerGUI.java, Button.java,
and Carrots.java.
• You MUST adhere to the course’s Academic Conduct Expectations and Advice.
• All implemented methods including the overridden methods MUST have their own javadoc-style
method headers, with accordance to the CS300 Course Style Guide.
1 Getting Started
Start by creating a new Java Project in eclipse. You can call it P04 Carrot Patch for
instance. You must ensure that your new project uses Java 11, by setting the “Use an execution
environment JRE:” drop down setting to “JavaSE-11” within the new Java Project dialog box.
Do NOT create a project-specific package; use the default package.
Download the images and processing core.jar
Next, download this P4Distributables.zip file, and extract the contents of this archive file
directly into your P4 project folder. This should add:
• a core.jar file which is part of the processing graphical library. You are welcome (but
not required) to read more about here. If this .jar file does not immediately appear in
the Project Explorer, try right-clicking your project in the project folder and selecting
“Refresh” to fix that. To use of the code within this jar file, you’ll need to right-click
on it within the Project Explorer and choose “Add to Build Path” from the “Build
Path” menu.
• a folder of images which contains the four following files: background.png, carrot.png,
rabbit.png, and wolf.png. The core.jar file .
The result of this operation on the Package Explorer is illustrated in Fig.2.
Figure 2: Eclipse Package Explorer
2 Create the CarrotPatch main class and download the
supportive code
Create a new class called CarrotPatch which includes a main() method. Your CarrotPatch
class MUST inherit from a class defined the core.jar file called PApplet (You’ll need to import
processing.core.PApplet for this to work). This makes your CarrotPatch class to BE of type
PApplet. PApplet models the Processing window for a graphic application or program. It
provides good ways to create a new window and draw graphics onto it. Note that in your
whole graphic application, only ONE PApplet object must be used. It is an instance of this
CarrotPatch class. All the visible and interactive objects including images which will be defined
in this application will be drawn in this CarrotPatch PApplet object.
2.1 CarrotPatch’s main() method
Now, define a main method to include only the following single statement.
PApplet.main(“CarrotPatch”); // do not add any other statement to the main method
// The PApplet.main() method takes a String input parameter which represents
// the name of your PApplet class.
This should result in a program that opens a small window when it is run. We won’t be adding
anything more to this main method for the rest of this assignment.
2.2 Download the supportive code
For this assignment, we give you a supporting code that you will start working on it and extend
it. Download each of the following files and make sure they are included in the same project
directly inside the default package in the src folder. If they do not immediately appear in the
Project Explorer, try right-clicking your project in the project folder and selecting “Refresh”
to fix that.
• interface GUIListener (GUIListener.java)
• class Button (Button.java)
• class Carrots (Carrots.java)
2.3 Define the CarrotPatch data fields
Your CarrotPatch class must contain the following instance data fields at the top of the
CarrotPatch class outside of any method.
• backgroundImage: private instance field of type PImage. It represents the background
image of this application. (You’ll need to import processing.core.PImage).
• objects: protected instance field of type ArrayList < GUIListener >. It stores all the
interactive objects which will be defined in this CarrotPatch graphic application.
Do NOT initialize any of the above data fields where they are defined. They will be initialized
in the setup() method.
2.4 Define the CarrotPatch methods
Your CarrotPatch class must contain and override the instance methods defined in the following
text file. There are five callback methods from the PApplet class to override: setup(),
draw(), mousePressed, mouseReleased(), and keyPressed. Note these methods are used
in a similar fashion to the setup (called once at the beginning of our program), draw (called
repeatedly while the program runs) mousePressed (called each time the mouse is pressed),
and keyPressed (called each time a key is pressed) methods from P2 Memory Game. Notice
that with respect to P2 implemented using procedural programming, this CarrotPatch class
which extends PApplet is implemented based on the Object-oriented programming paradigm.
All the callback methods are instance methods (versus static methods in P2). Some other
PApplet methods are new such as settings() and some graphic setting features implemented in
the private method CarrotPatchSettings() called in the setup() method).
In addition to the callback methods, the CarrotPatch class defines an instance method called
removeAll which removes all carrots and animal objects already present in the patch. We are
going to complete the implementation of the missing code (see TODO tags) as we go throughout
this write-up.
2.5 Initialize the CarrotPatch instance fields
To start, initialize the objects list to an empty ArrayList in the setup() method. Then, load
the background image in the setup() method using PApplet.loadImage() method as follows.
backgroundImage = this.loadImage(“images” + File.separator + “background.png”);
Then, draw it to the center of the screen at the beginning of the draw method using the using
the PApplet.image() method as follows.
this.image(backgroundImage, this.width / 2, this.height / 2);
Recall that the setup() method is a callback method called only one time when the graphic
application starts. Now, running this program will now result in a window showing the
background image as depicted in Fig.3. Next, let’s explore the other provided source files
before we proceed.
Figure 3: Carrot Patch Background Screen
3 Explore the supportive code
3.1 GUIListener interface
Our P04 Carrot Patch program is a graphical application which interacts with the user via a
Graphical User Interface (GUI). For instance, our program waits for a user input as one of the
following events: press on the mouse button, release the mouse, drag an image, etc. Then,
when such event is detected, a particular method is invoked.
Our application will contain different graphic objects (buttons and animals as shown above
in Fig.1). These objects will be drawn repeatedly to the display window. They will listen
to the mouse events and must react appropriately to them each time the mouse is pressed or
released. To avoid redundancy and promote abstraction in our code, we defined the interface
GUIListener (GUI refers to Graphic User Interface). You can notice that this interface contains
the signatures of the following methods ONLY without any implementation details.
public interface GUIListener {
public void draw(); // draws this interactive object to the display window
public void mousePressed(); // called each time the mouse is Pressed
public void mouseReleased(); // called each time the mouse is Pressed
public boolean isMouseOver(); // checks whether the mouse is over this GUIListener object
Recall that an interface cannot be constructed. We can define a reference of type GUIListener.
It can store the reference to any object instance of a class which implements this interface.
3.2 Button class
You can notice from the final display window for our CarrotPatch application shown in Fig.1,
that we are going to add four buttons “Plant Carrots”, “Add Rabbit”, “Add Wolf”, and
“Restart”. All these buttons will define a similar state (data fields) and share similar functionalities.
Therefore, we created the class Button to serve as the base class (aka super class) for each of
the specific Button classes that we will create later in this assignment. Each button will be
drawn to display window, listen and react to the mouse events. Therefore, the class Button
implements our GUIListener interface and overrides all its methods.
Note that the Button class contains the following fields.
private static final int WIDTH = 85; // Width of this Button
private static final int HEIGHT = 32; // Height of this Button
protected static CarrotPatch processing; // PApplet object where this button
// will be displayed
private float[] position; // array storing x and y positions of this Button
// with respect to the display window
protected String label; // text/label that represents the name of this button
Notice carefully that the Button class defines one protected static field named processing of
type CarrotPatch. It represents the graphic display window of this application where all the
buttons will be drawn and will operate. It is protected. So, it is directly visible to all the
subclasses of the class Button.
This class implements two constructors, a static setter method to set the processing field, and
overrides the four methods defined in the GUIListener interface. Make sure to read through
the class definition of the Button class and its implementation. To help you further understand
the code for drawing a button, we note that we used the following processing methods defined
in the PApplet class.
• rect(): This is the processing method for drawing a rectangle. It takes four parameters:
1) the x-position of the upper left corner, 2) the y-position of the upper left corner,
3) the x-position of the lower right corner, 4) the y-position of the lower right corner.
These corner positions must be calculated so that the button appears centered around
it’s position field with the appropriate WIDTH and HEIGHT.
• fill(): This method is used to set the drawing color. When the mouse is over a button, its
filling color is set to dark gray by calling fill(100), and when the mouse is not over this
button, its filling color is set to light gray fill(200)
• text(): This processing method is used to draw a text to the display window. The
PApplet.text() method takes three parameters: 1) the string of text to draw, 2) the
x-position that this text should be centered around, and 3) the y-position that this text
should be centered around.
Note that since our CarrotPatch class extends PApplet. All these public methods defined in
the PApplet class must be directly accessible through the Button.processing data field of type
3.3 Carrots class
The Carrots class models a list of the carrots planted in the carrot patch. This class will not
be instantiable. It defines static data fields and implements static methods ONLY. The carrots
will be visible objects in this patch (meaning instances of processing.core.PImage class). They
do not interact with the mouse events. They are NOT GUIListener objects.
Notice that the Carrots class defines one static field of type CarrotPatch which represents the
PApplet object where the carrots will be drawn. The Carrots class also defines a perfect size
array of the potential positions of the carrots in the display window and a perfect-size array
of the planted carrots. We invite you to read through the provided implementation of the
class Carrots and its different methods. Do not hesitate to contact your instructor or any of
our consultants or post a question on piazza if you have a question about any of the provided
3.4 Set processing for the Carrots and Button classes
Now, let’s set the processing CarrotPatch display window for the Carrots and the Button classes.
In the CarrotPatch.setup() method, call the Carrots.settings() and the Button.setProcessing()
methods and pass them a reference to the current CarrotPatch object (which is the reference
4 Create and add specific buttons
Now Create the four following classes. They MUST extend the Button base class. This makes
them all of type GUIListener since the Button class implements that interface.
• PlantCarrotsButton extends Button
• AddRabbitButton extends Button
• AddWolfButton extends Button
• RestartButton extends Button
All these classes must define the following instance methods. No specific data fields are defined
in these classes.
• One constructor which takes two float variables as input parameters. The first float
represents the x-position of the button. The second float represents the y-position of the
button. Each of these constructors calls the constructor of the superclass Button(String,
float, float). The String labels of the four specific buttons are as follows:
– “Plant Carrots” for the PlantCarrotsButton,
– “Add Rabbit” for the AddRabbitButton,
– “Add Wolf” for the AddWolfButton,
– “Restart” for the RestartButton,
• Only the public instance method mousePressed() must be overridden in each if the 4
specific button classes. At this stage, you can add a specific print statement which will
be displayed to the console (not on the graphic display window) when the mouse is
pressed and is over each specific button. For instance, this can be an implementation of
PlantCarrotsButton.mousePressed() method. We are going to change it later.
if (isMouseOver()) {
System.out.println(“Plant Carrots Button Pressed”);
Now, instantiate in your CarrotPatch.setup() method the following four buttons and add
them to the objects ArrayList. Recall that the Button class implements the GUIListener.
• an instance of PlantCarrotsButton at position (43, 16),
• an instance of AddRabbitButton at position (129, 16),
• an instance of AddWolfButton at position (215, 16),
• an instance of RestartButton at position (301, 16); where position(x,y) represents the xand y-coordinates where the related button will be placed in the screen display window.
Note that each reference of type Button or its subclasses can be safely cast to the type
GUIListener and stored in the objects ArrayList.
4.1 Click on buttons
To use these buttons, we have to update first the implementation of the CarrotPatch.draw(),
CarrotPatch.mousePressed(), and CarrotPatch.mouseReleased() methods as follows.
• In the CarrotPatch.draw() method, after drawing the background image, draw the
planted carrots first by calling Carrots.draw() method. Then, traverse the contents of the
ArrayList objects and draw each of the interactive objects stored there.
• In the CarrotPatch.mousePressed() method, traverse the ArrayList objects and call
the mousePressed() method of the first clicked element ONLY.
• In the CarrotPatch.mouseReleased() method, traverse the ArrayList objects and call
the mouseReleased() method of every element stored in the list.
Running the program will result in the display window comparable to the one provided in Fig.4
where the buttons have been clicked in this order: (1) “Plant Carrots”, (2) “Add Rabbit”,
(3) “Add Wolf”, and (4) “Restart”. Notice that clicking on the different buttons will print
the specific behavior implemented in the mousePressed of each button. Notice the power of
polymorphism. Even though the arraylist objects stores elements of type GUIListener, each
element performs differently with respect to the implementation of the mousePressed() method
overridden in its most specific type.
Figure 4: CarrotPatch with 4 buttons
4.2 Update the implementation of PlantCarrotsButton.mousePressed()
Now, you can implement the specific behavior of the PlantCarrotsButton when clicked. You can
comment the print statement in the PlantCarrotsButton.mousePressed() method and instead
call the Carrots.plant() method which is going to plant carrots in all the available spots within
the Carrots.carrots array. Before checking whether this code will work or not, double check
that the Carrots.draw() method call is added to the CarrotPatch.draw() method just before
drawing the interactive objects stored in the objects arrayList.
This done, running your program and then clicking on the “Plant Carrots” button should result
in a display window comparable to the one shown in Fig.5.
Figure 5: Plant Carrots Button Clicked
5 Create Animal base class
Now create a new class called Animal. This class MUST implement the GUIListener interface.
It plays the role of a base class of any specific animal type such as Rabbit and Wolf which will
be implemented in the next steps of this assignment. The class Animal defines the following
data fields.
private static Random randGen = new Random(); // Generator of random numbers
protected static CarrotPatch processing; // PApplet object representing the display window
protected PImage image; // image of this
protected String label; // represents the name/identifier of this animal
private int x; // x-position of this animal in the display window
private int y; // y-position of this animal in the display window
private boolean isDragging; // indicates whether the animal is being dragged or not
private int oldMouseX; // old mouse x-position
private int oldMouseY; // old mouse-y position
It also defines the two following constructors (available on this supportive source file).
* Creates a new Animal object positioned at a given position of the display window
* @param processing PApplet object that represents the display window
* @param x x-position of the image of this animal in the display window
* @param y y-position of the image of this animal in the display window
* @param imageFileName filename of the animal image
public Animal(int x, int y, String imageFileName) {
// Set Animal drawing parameters
this.x = x; // sets the x-position of this animal
this.y = y; // sets the y-position of this animal
this.image = processing.loadImage(imageFileName);
isDragging = false; // initially the animal is not dragging
* Creates a new Animal object positioned at a random position of the display window
* @param processing PApplet object that represents the display window
* @param imageFileName filename of the animal image
public Animal(String imageFileName) {
this(randGen.nextInt(processing.width), Math.max(randGen.nextInt(processing.height), 200),
In addition, we provide you with the implementation of the GUIListener.draw() method and a
few setter and getter methods in this text file. Read carefully through the implementation of
the method Animal.draw(). Try to understand how the behavior of dragging an animal such
that it follows the mouse moves when clicked and dragged has been implemented.
Override GUIListener abstract methods
The class Animal MUST override all the abstract methods defined in the GUIListener. Therefore,
you MUST override on your own the following methods.
public boolean isMouseOver() {} // checks whether the mouse is over this animal
public void mousePressed() {} // starts dragging this animal by setting its isDragging
// field to true if the mouse is pressed and is over this animal
public void mouseReleased() {} // stops dragging this animal by setting its
// isDragging field to false
Animal class additional behaviors
Besides, the Animal class defines the following behaviors. Implement the two versions of the
overloaded method isClose() with respect to their specification provided in their javadoc style
method headers comments. Notice that a method called distance to compute the euclidean
distance between the current animal and a given (x,y) position was provided for you. DO NOT
make any change to the action() method. A default animal does not perform any action in
this CarrotPatch application. This method must be overridden by the derived classes. Note that
every animal has a continuous behavior. Therefore, call action() method from the Animal.draw() method.
* Checks whether this animal is within a distance range with respect to a
* given (x,y) position. It returns TRUE if this animal is located within a
* range distance [0 .. range] around the provided position and FALSE otherwise.
* @param x a given x-position
* @param y a given y-position
* @param range radius of the neighborhood range from the given (x,y) position
* @return true if otherAnimal is close to this animal with respect to range
public boolean isClose(int x, int y, int range) {
// TODO implement this method
* Checks whether this animal is within a distance range with respect to anotherAnimal.
* It returns TRUE if otherAnimal is located within a range distance [0 .. range]
* around the current animal and FALSE otherwise.
* @param otherAnimal an animal to check if it is close to this animal
* @param range radius of the neighborhood range from the position of this Animal
* @return true if otherAnimal is close to the current tiger
public boolean isClose(Animal otherAnimal, int range) {
// TODO implement this method
* Continuous behavior performed by this animal in the carrot patch
public void action() {
// This method should be overridden by a subclasse
Set the processing field of the class Animal in the CarrotPatch.setup() method
Notice also that all the animal objects share the same static field processing of type CarrotPatch
which stores the reference to the PApplet display window of this application. Make sure to
call the Animal.setProcessing() method in the CarrotPatch.setup() method to set the
processing field of all animals to the current CarrotPatch object this.
6 Create and implement Rabbit class
Now, let’s create the class Rabbit. This class represents the Rabbit animal. It MUST extend
the Animal class. Rabbits can be added to randomly positions to the CarrotPatch application.
They can move in the patch. They watch out for wolves and when they are clicked they make
one hop towards a carrot. They also eat carrots. Every created Rabbit has their own label in
the format R#. The first created Rabbit is labelled R1, the second R2, the third R3, and so
6.1 Define Rabbit’s data fields, constructor, and getter methods
Here is a list of the data fields, and a provided implementation of the constructor of the class
Rabbit. Note that the constructor of the class Rabbit creates a new Rabbit located at a Random
position of the display window and initializes its instance fields.
private static final String RABBIT = “images”+ File.separator + “rabbit.png”;
private static final String TYPE = “R”; // A String that represents the rabbit type
private static int hopStep = 70; // one hop step
private static int scanRange = 175; // scan range to watch out for threats
private static int nextID = 1; // class variable that represents the identifier
// of the next rabbit to be created
private final int ID; // positive number that represents the order of this rabbit
* Creates a new rabbit object located at a random position of the display window
public Rabbit() {
// Set rabbit drawing parameters
// Set rabbit identification fields
ID = nextID;
this.label = TYPE + ID; // String that identifies the current rabbit
// getter of Rabbit.scanRange static field
public static int getScanRange() {}
// getter of Rabbit.hopStep static field
public static int getHopStep() {}
6.2 Add new Rabbits to the carrot patch
Before implementing the specific behaviors related to Rabbit objects, let’s try to add new
Rabbits to our CarrotPatch. To do so,
1. Update the AddRabbitButton.mousePressed() method such that a new instance of the
Rabbit class is created and added to the CarrotPatch.objects arraylist each time the
mouse is pressed and is over a AddRabbitButton object. Notice that the objects array
list is a protected instance field accessible directly using the Button.processing static field
visible to the AddRabbitButton class.
2. Update the CarrotPatch.keyPressed() method such that a new Rabbit is added to the
CarrotPatch’s objects array list each time the R-key is pressed.
Now, if you run your program, a new Rabbit will be added to the carrot patch graphic display
window at random positions each time the R-key is pressed or the “Add Rabbit” button is
clicked. The Fig.6 shows an example of this application run at this level.
Note also that even though you did not make any further change to the program, the added
rabbit objects respond to the mouse events. These behaviors have been already implemented in
the Animal class and Rabbit IS-An Animal. If the rabbits do not follow the mouse moves when
they are dragged, review your implementation of the Animal.isMouseOver(), Animal.mousePressed(),
and Animal.mouseReleased() methods.
7 Create and implement Wolf Class
Now create a new class called Wolf which extends the Animal class. This class models wolves
objects in the CarrotPatch. Wolves are looking for rabbits in the patch to eat them.
7.1 Define the Wolf ’s data fields
The class Wolf defines the following data fields.
// path to the wolf image file
private static final String WOLF = “images” + File.separator + “wolf.png”;
Figure 6: Rabbits in the Carrot Patch
private static int scanRange = 120; // scanning range to look for a rabbit
// in the neighborhood
private static int nextID = 1; // identifier of the next Wolf to be created
private static final String TYPE = “W”; // A String that represents the Wolf type
private final int ID; // positive number that represents the order of this Wolf
private int rabbitEatenCount; // Number of rabbits that the current Wolf has eaten so far
7.2 Implement the constructor and getter methods of the Wolf class
Your Wolf class MUST define only one no-argument constructor which must create a new wolf
and initialize its instance fields. Wolves are created at the same fashion of creating new rabbits.
A new wolf is labelled W#. The first created walf is named W1, the second is named W2, the
third is named W3, and so on. Wolves will be created at random positions within the display
* Creates a new Wolf object at a random position of the display window
* @param processing CarrotPatch object which represents the display window
public Wolf() {}
In addition, implement the following getter methods.
public int getRabbitEatenCount(){} // gets rabbitEatenCount instance field
public static int getScanRange(){} // gets the scanRange of a Wolf
7.3 Add new Wolves to the Carrot Patch
To add new wolves and display them to the CarrotPatch, update the CarrotPatch.keyPressed()
and the AddWolfButton.mousePressed() methods as follows.
1. Update the AddWolfButton.mousePressed() method to instantiate a new Wolf object
and add it to the CarrotPatch.objects arraylist each time an AddWolfButton object is
2. Update the CarrotPatch.keyPressed() method such that a new Wolf is created and
added to the CarrotPatch’s objects array list each time the W-key is pressed.
Running the program and clicking on “Plant Carrots”, “Add Rabbit”, “Add Wolf” buttons, or
pressing the R-key or W-key will result in an interactive interface comparable to the one shown
in Fig.7. Notice that the animals (whether wolves or rabbits) drawn in the graphic display
window can be dragged with response to the mouse moves. If two or more animals overlap,
and the user tries to drag them, only the oldest animal added to the patch will be dragged.
7.4 Remove animals from the Carrot Patch
Now, implement removing an animal from the Carrot Patch when the mouse is over it and the
”D-Key” is pressed. To do so, update the implementation of the CarrotPatch.keyPressed()
method to implement this behavior. Traverse the objects list and remove the first animal
whose isMouseOver() returns true. Keep in mind that the objects list contains GUIListener
references of different specific types (buttons and animals). Make sure to consider only instances
of the Animal class in your search.
After implementing this behavior appropriately, run your program and check whether a wolf
or a rabbit is removed from the CarrotPatch each time the D-key is pressed while the mouse is
over it.
Figure 7: Rabbits and Wolves in the Carrot Patch
8 Implement RestartButton.mousePressed() behavior
Go to the CarrotPatch class and try to implement the CarrotPatch.removeAll() method
with respect to its specification and the provided hints. Then, update the implementation of
the RestartButton.mousePressed() behavior. When the mouse is pressed and is over the
RestartButton button, all the planted carrots and all the animals must be removed from the
CarrotPatch. Next, run your program and check whether this functionality works as expected.
9 Develop unit tests
Now that Rabbits and wolves can be added to the CarrotPatch, we can implement a few test
methods to assess the correctness of the Animal.isClose() methods. Create a new class called
CarrotPatchTester and add it to your project. This class MUST extend the CarrotPatch
class and override its setup() method.
You can download the starter code for the CarrotPatchTester here. We provide you with
an example showing how to define test scenarios for test1isCloseMethod(). You can make
calls to your test methods in the overridden setup() method. Feel free to reuse the provided
implementation verbatim in your CarrotPatchTester class. You can also inspire by these
examples and define your own scenarios for that test method. You MUST implement the
test2isCloseMethod() and test3isCloseMethod() test methods.
In the next sections, we are going to implement the specific actions performed by Rabbit and
Wolf objects in the CarrotPatch.
10 Implement the Rabbit specific behaviors in the CarrotPatch
In the Carrot Patch, our rabbit objects implement the following two behaviors.
• Each time a rabbit is clicked, it will make ONE hop step towards the first available carrot
in the carrot patch. If it reaches the carrot, it will eat it.
• Each rabbit is going to watch for wolves in their scan range neighborhood. If a rabbit
detects at least one close wolf, it displays a warning message on the graphic display
10.1 Rabbit hops toward a carrot when clicked
To implement this behavior, add the following method to your Rabbit class.
* Gets the first carrot in the patch. If the carrot is in the Rabbit
* hopStep range, the rabbit eats it. It sets its position to the (x,y)
* position of the carrot and the carrot will be removed from the Carrot Patch.
* Otherwise, the rabbit moves one hopStep towards that carrot. If no carrot
* found (meaning Carrots.getFirstCarrot() returns false),
* the rabbit does nothing.
public void hopTowardsCarrot() {
// get the first carrot
int[] carrot = Carrots.getFirstCarrot();
if (carrot != null) {
// TODO complete the implementation of this method
To help you implement this method, we recommend that you review the Carrots.getFirstCarrot()
and Carrots.remove(int) methods. Besides, we provide you in the following with a hint on
how to calculate the new position (newX, newY) of an object located at (oldX, oldY) position
when moving towards a destination located at (destinationX, destinationY) position with a
moveDistance. We denote the euclidian distance between destination and object before moving
by d. In our case, if a rabbit is going to make one hop towards a carrot as destination, hopStep
is the moveDistance, and newX, newY will be its new (x,y) position after performing the ONE
newX = oldX +
moveDistance ∗ (destinationX − oldX
newY = oldY +
moveDistance ∗ (destinationY − oldY
d = (int)M ath.sqrt(dx ∗ dx + dy ∗ dy)
where dx = destinationX − oldX and dy = destinationY − oldY
Override the mousePressed() method in the Rabbit class
Once your hopTowardsCarrot() is implemented, override the the mousePressed() method in
the Rabbit class. This will be a partial overriding as follows.
public void mousePressed() {
// call the mousePressed defined in the Animal super class
// call hopTowardsCarrot() method
Now, run your program, plant carrots, add at least one rabbit, then try clicking on one rabbit
and check whether it will make one hop towards the first carrot after each mouse click. If the
rabbit reaches the carrot, it will eat it. It takes its position, and the carrot is removed from
the patch. If you keep clicking on the rabbit (simple clicks without dragging it), the rabbit will
hop towards the next carrots, and eats them one by one.
10.2 Override the Rabbit.action() behavior
We define the following action of a rabbit in the carrot patch. A rabbit will continuously scan
the area around it watching for a threat (i.e. if there is at least one wolf located nearby). If
so, it will react by displaying an alert message ”WOLF!”. We provide you in the following
with the implementation of the Rabbit.action() method. To enable it, you must implement the
watchOutForWolf() behavior.
* This method watches out for wolves. Checks if there is a wolf
* in the Rabbit.scanRange of this Rabbit.
* @return true if the current rabbit is close to at least one wolf
public boolean watchOutForWolf() {
// TODO complete the implementation of this method
// Traverse the processing.objects arraylist checking
// whether there is a wolf which is close by Rabbit.scanRange
// of this rabbit.
return false;
* Watches out for a wolf and display a Warning message “WOLF!”
* if there is any wolf in its neighborhood.
public void action() {
if (watchOutForWolf()) {
// this.setScaredImage();
processing.fill(0); // specify font color: black
processing.text(“WOLF!”, this.getX(), this.getY() – this.image.height / 2 – 6);
Note that you do not need to call Rabbit.action() method. It is already called in Animal.draw()
method. Polymorphism is MAGICAL!
To help you assess the correctness of your Rabbit.watchOutForWolf() method, we provide
you with the implementation of these test methods. You can use them verbatim in your
CarrotPatchTester class and call them from the CarrotPatchTester.setup() method.
11 Implement the Wolf action in the CarrotPatch
In our carrot patch, we have HUNGRY wolves. Each wolf is looking for rabbits in its scan
range to eat it. To implement this behavior, follow the following steps.
11.1 Implement eatRabbit() method
Add the following method eatRabbit() to the Wolf class and implement it.
* Moves to the position of the specified rabbit passed as input, and eats it.
* The eaten rabbit will be removed from the patch and he number of eaten
* rabbits by this wolf is incremented by one.
* @param rabbit rabbit to eat by this wolf
public void eatRabbit(Rabbit rabbit) {
// if the mouse is over the current Wolf, release it so the Wolf can move
// ahead to the position of rabbit and eat it.
if (isMouseOver())
// 1. set the position of the current Wolf to the position of the rabbit
// 2. remove the rabbit from the patch
// 3. increment the number of eaten rabbits by one
To help you assess the correctness of your Wolf.eatRabbit() method, we provide you with the
implementation of this test method. You can use it verbatim in your CarrotPatchTester class
and call them from the CarrotPatchTester.setup() method. Feel also free to define further test
11.2 Override action() method
Next, override the Wolf.action() method as follows.
* Defines the action of this wolf in the carrot patch. This wolf lookup for
* rabbits in its neighborhood (Wolf.scanRange) and eats the first found rabbit
* only. This method also displays the number of rabbit eaten by this wolf if any.
public void action() {
//Traverse processing.objects arraylist, search for the first rabbit which
// is close to this wolf with respect to Wolf.scanRange, and eats it.
// If no rabbit is found in the neighborhood, nothing will be done.
if (rabbitEatenCount > 0)
displayrabbitEatenCount(); // display rabbitEatenCount
* Displays the number of eaten rabbits if any on the top of the Wolf image
public void displayrabbitEatenCount() {
processing.fill(0); // specify font color: black
// display rabbitEatenCount on the top of the Wolf’s image
processing.text(rabbitEatenCount, this.getX(), this.getY() – this.image.height / 2 – 6);
12 Assignment Submission
Congratulations on finishing this CS300 assignment! After verifying that your work
is correct, and written clearly in a style that is consistent with the CS300 Course Style
Guide, you should submit your final work through gradescope.com. The only NINE files
that you must submit include: CarrotPatch.java, Animal.java, Rabbit.java, Wolf.java,
PlantCarrotsButton.java, AddWolfButton.java, ResetButton.java, and CarrotPatchTester.java.
Your score for this assignment will be based on your “active” submission made prior to the hard
deadline. The second portion of your grade for this assignment will be determined by running
that same submission against additional offline automated grading tests after the submission
deadline. Finally, the third portion of your grade for your submission will be determined by
humans looking for organization, clarity, commenting, and adherence to the CS300 Course Style
©Copyright: This write-up is a copyright programming assignment. It belongs to UW-Madison. This
document should not be shared publicly beyond the CS300 instructors, CS300 Teaching Assistants, and CS300
Spring 2021 fellow students. Students are NOT also allowed to share the source code of their CS300 projects
on any public site including github, bitbucket, etc.
Extra Challenges
Here are some suggestions for interesting ways to extend this CarrotPatch graphic application,
after you have completed, backed up, and submitted the graded portion of this assignment.
No extra credit will be awarded for implementing these features, but they should
provide you with some valuable practice and experience. DO NOT submit such extensions via
1. Suggestion 1 – Try updating the way how a rabbit hops towards a carrot in the patch.
Instead of moving forward the first non null position in the Carrots.carrots array, the
rabbit can move forward the closest carrot to its current position.
2. Suggestion 2 – Try expanding the possible actions performed by a wolf or a rabbit in
the carrot patch. Use your imagination!
3. Suggestion 3 – Try creating new animal classes with different data fields and different
behaviors. For instance, you can define birds which tweet and jump on the trees or fly in
the sky. Use your imagination!