Problem Solving Assignment 8

Due Monday, February 19 at 11:59pm PST

Notes:

• This IS a pair assignment. You MUST do the assignment with your partner.

• You must complete an interview with a Lab Tutor for this PSA. Interviews are individual (partly to ensure that one partner doesn't do all the work). See instructions here for more details.

• This work should be done in its own directory called 'psa8'. Instructions here.

• This assignment has sample solution code that you can run on ieng6. You won't be able to see the java code itself =) but you will be able to do tests to see what it does, and make sure yours does the same thing. YOUR CODE MUST DO THE EXACT SAME THING. EXACT!! Wording, spaces, everything. Instructions on how to run the sample solution code are here .

• Each file must have a header with the team members' names, logins, and PIDs. The header should also describe the program in 2-3 sentences.

This homework requires skills from Chapter 1 through Chapter 6.

Problem

Write a program that simulates a population of Amoebas who float around and absorb each other until there is only one left.

Introduction:

• The Amoebas will be represented in the graphics screen by circles of different colors and different sizes.
• They float in a certain direction until they hit one of the 4 edges of the window, then they "bounce" off.
• If two Amoebas collide, the larger one eats and absorbs the smaller one.

Details:

• Important: This is another graphics problem, like the Turtle in PSA 4 and GalileoUhoh in PSA 6. So you will probably want to work mostly in the lab instead of from home. Refer to the PSA 4 description and webboard posts for how to get X-11 forwarding working, and so on.
• First, you need to make a class Circle that draws circles (which will be used to make the Amoebas). The code is almost exactly the same as the Circle class you used for GalileoUhoh. Copy the new Circle class starter code (-bash2.05$ cp ~/../public/Circle.java ~/psa8/). You will be adding the following features to the Circle class:
  1. Two new integer instance variables v_x and v_y. These represent the velocity of the Amoeba as it floats around (how far it moves each time it moves in the x direction and how far in the y direction). Velocity is normally a vector. We're representing it as two integers--the x component and the y component--separately. More detail on how velocity works is in the move method.
  2. Two new integer instance variables world_width and world_height. These represent the width and height of the graphics window (so you can calculate if the circle is in-bounds).
  3. Add these variables to the Circle class constructor. The constructor will now have 9 parameters: radius, center x and y, color, velocity x and y, world width and height, and a special parameter "g" (that is for the graphics stuff).
  4. Find methods isOutOfBoundsX() and isOutOfBoundsY() in Circle.java. They are currently empty. Fill them in so that they check if the parameter would be a valid x or y coordinate for the Circle. In other words, no part of the Circle would be off-screen if the center of the Circle was there. For x, check both off the window to the left (less than zero) and right (greater than world_width). Likewise for y, top (zero) and bottom (world_height). But remember to count the Circle's radius as well.
  5. Add code at the VERY beginning of the setLocation() method that checks the parameters to the method to make sure they aren't trying to move the circle out-of-bounds. (use the new isOutOfBoundsX() and isOutOfBoundsY() methods) Change setLocation() so it returns a boolean. If one of the parameters is illegal (or both are illegal), the DO NOT move the circle, just return false. If both parameters are OK, then move the circle (that code is already there) and at the end return true.
  6. Add code at the VERY beginning of the setRadius() method that checks the parameter to make sure it is valid (radius is not a negative number). As with setLocation(), change setRadius() so it returns boolean--false if there was a problem with the parameter, otherwise true. Do not change the radius if there was a problem with the parameter.
  7. Add a new method isBiggerThan(). It takes one parameter, a Circle object. It returns true if the calling object has a bigger radius than the parameter object. Otherwise it returns false.
  8. Add a new method isCollidingWith(). It takes one parameter, a Circle object. It returns true if the calling object and the parameter object are touching or overlapping. (Hint: you can check this by seeing if the distance between the two center points is less than or equal to the sum of the two radii. Two calculate the distance between two points that you have (x,y) coordinates for, you need to use the Euclidean distance formula. There is a method provided for you in Circle.java that calculates the distance between two points using this formula.) UPDATE 7pm 2/28/07: I changed the Euclidean distance method in the starter code for the Circle class so that instead of taking all the individual x and y values, it just uses the calling Circle and the parameter Circle directly. If you already got the old one, you can either just go ahead with it, or you can change to the new one, whichever you prefer. There was nothing *wrong* with the original, I just think the new one is easier to understand (and it is better Object-Oriented Design--see, OOD does make code easier to understand!!)
  9. Add a new method mergeWith(). This will represent two Circles (amoebas) merging into one bigger one. It takes one parameter, a Circle object. It does not return anything. What it does is set the calling object's values (location of the center, velocity and color) to be the values of the bigger of the two circles. (note that this means that if the calling circle is the bigger one, its values stay the same--except radius see next point--) For the radius, do something slightly different. The radius of the calling object is set to be the sum of the radii of the two circles (be sure to use setRadius() to do this so that it calls the GUI erase() and draw() stuff correctly). Note: before doing anything else, call erase() on the circle that was passed as a parameter since it is being eaten/absorbed.
  10. Add a new method move() that moves the circle according to its velocity. Each time move() is called, the center_x and center_y values will be updated. To get the new location of the circle's center, add v_x to center_x, and add v_y to center_y. Calculate the new x and y values, but before you move the circle you need to check that they are legal values (use the isOutOfBoundsX() and isOutOfBoundsY() methods). If the new value for center_x is illegal, then you need to have the ball "bounce" by going in the opposite direction. (Hint: the definition of opposite direction here is that if v_x is positive, it should be changed to the same number but negative, and if it is negative it should be changed to positive). Then perform the same check on center_y and do the same "bounce" effect. If you changed v_x or v_y, redo your calculation of the x and y values for the circle's location (note that if only the x part was illegal, you don't do anything to v_y, and if only the y part was illegal, you don't do anything to v_x). Finally, move the circle to the new location. Make sure you use setLocation() to do this, so that it will do the GUI erase() and draw() stuff correctly. Note that because we are detecting that a Circle would move off the board if it moved and not doing that move and bouncing in the other direction, it might sometimes be visible to the naked eye that a Circle is bouncing too soon (not actually touching the wall). That's ok, you'll notice the sample does this as well.
  11. Add a toString() method. This will help with your debugging and help the graders with grading. Your method should return a String version of center_x, center_y, v_x, v_y, and the radius, with a nice format (label each value). Note that toString() does not itself print the values to the screen, it just returns a String.
• Now, make a separate class AmoebaWorld that will use your Circle class. This class is in a file called AmoebaWorld.java. Again, we have provided some starter code (-bash2.05$ cp ~/../public/AmoebaWorld.java ~/psa8/).
• In AmoebaWorld, we have already set up the animation window. We have also started to set up a set of 30 balls with different colors, different locations and different sizes. However, all we have done is set up the values that should be sent to the Circle class constructor for each Circle object--the actual call to the constructor is missing. Add one line of code that instatiates the Circle by calling the constructor with all 9 parameters.
• You will see a while loop in the provided code. In the while loop, do the following:
  1. Pause for 500ms (this code is already there for you)
  2. Then loop over each Circle and move it
  3. After moving all the Circles, loop starting at the beginning of the amoebas array and check if each Circle (amoeba) has collided with any other Circle (hint: nested for loops!).
  4. If you find two Circles that are colliding, then merge them. Recall that merging causes all the values to be set in the calling Circle which is now bigger (it "ate" the other one), so you need to get rid of the other one. Do this by setting it to null in the array. Eventually, more and more elements of the array will be null. The nulls will be spread all around in the array (unlike the partially-filled arrays you used in the past, like for ContactsList, where they were all at the end) This means that before you do anything with a Circle object from the array you need to check if it is really a Circle object, or if it is null (to prevent a NullPointerException--see your book if you don't know what that means).
• Be sure to check the sample solution.
• Here are some pics showing how the world starts out with many different amoebas, but slowly they absorb each other until there is only one megasize amoeba:
  
  
  
  
  
  

Details

Start by creating a directory (folder) in your ieng6 cs8fzz account (this is necessary for the bundle script). After you log in, create a directory by typing the commands:

-bash-2.05b$ mkdir psa8

Go into that directory (like double clicking to open a folder) with the command:

-bash-2.05b$ cd psa8 

Note: you must name your directories (folders) and files as indicated in the problem descriptions for the turn in program to work.

To run a sample of AmoebaWorld, since it has graphics, you will need to do something different and run the class directly. Do:

-bash-2.05b$ cd ~/../public/
-bash2.05$ java AmoebaWorld

The to return to your own directory, do "cd ~/psa8".

This assignment is worth 20 points.

General (4 pts):
• 1 Point: For proper formatting. Your code is properly and consistently indented.
• 1 Point: For documentation. You must write a 2-4 sentence description of the program (as a comment) that provides insight into what the program does and what it's useful for. In this header comment, you are also required to put the author names, author PIDs and author logins
• 2 points: Interview (done individually) see instructions here

  Circle.java (11 pts):

• 1 point: Add new instance variables and change constructor
• 2 points: Fill in isOutOfBoundsX() and isOutOfBoundsY()
• 1 point: Changes to setLocation() and setRadius()
• 1 point: Add isBiggerThan()
• 1 point: Add isCollidingWith()
• 1 point: Add toString()
• 2 points: Add move()
• 2 points: Add mergeWith()

  AmoebaWorld.java (5 pts):

• 1 point: Instantiate amoebas
• 2 points: Move amoebas around the world
• 2 points: Colliding amoebas merge

How to turn in your homework electronically

When you are ready to turn in your homework, run bundle-psa8 from your psa4 directory. The session should look like this:

-bash-2.05b$ cd ~/psa8
-bash-2.05b$ bundle-psa8
Good; all required files are present:

	Circle.java
	AmoebaWorld.java

Do you want to go ahead and turnin these files? [y/n]y
OK.  Proceeding.


Performing turnin of approx. XXXX bytes 
Copying to /home/linux/ieng6/cs8w/turnin.dest/cs8wzz.psa8
.
Done.
Total bytes written: XXXX 
Please check to be sure that's reasonable.
Turnin successful.

If you want to make changes after you've turned in your homework, make the changes and run bundle-psa8 again. The program will warn you that a "previously turned-in file exists" and ask if "you wish to over-write this existing file" (delete the old version and replace it with this new one). Respond in the affirmative by typing y and pressing the Enter key.

10% of your grade on this assignment will come from an interview you will have with one of the tutors during Open Lab Hours. You have 48 weekday hours after the electronic turnin deadline to get your interview done. The deadline for the interview for PSA 5 is Monday, Feb 19, theoretically at midnight, but actually by the end of the last tutor hour scheduled. You get an interview by going into B260 during a scheduled tutor hour. Find the tutor, ask them if you can interview for PSA 5. If they have others who are waiting for interviews, your name will go on the end of the list of people waiting. Interviews take about 5 minutes each. It is your responsibility to go in early enough that you can get your interview completed. If everyone waits until the last hour on Wed, this will not work. The tutor will ask you to log in, change to the directory where your work is (psa8) and then to follow their directions. They will ask you to run your program to show that it works, open files in your favorite editor, and ask you questions about how your code works. Additionally, they may question you as to how you would (theoretically) make small changes to the program to have it do something slightly different. Learning to be able to explain your problem solving process and discuss code with another human being is a very important professional skill. We hope that this process will help you develop this skill.

Copying the assignment directory to partner's home directory

You can copy the psa8 directory and its files to your partner's home directory by:

bash% scp -r psa8 cs8wxx@ieng6.ucsd.edu:

(don't forget the colon at the end of the command) where cs8wxx is your partner's username. You must be in the parent directory of the psa4 directory. So, you if you are currently in the psa4 directory you should execute "cd ..". Similarly, if the psa8 direcory is in your home directory then you have to be in your home directory. If you aren't there just execute "cd ~" and you'll be there. Your partner is required to enter his password when you enter the scp command. To check if the copy worked, your partner must login and ckeck if the psa8 directory exists in his home directory and if the proper files are located in it. This can be done by executing: "ls ~/psa8". The files in the psa4 directory should be listed.