Graphic by Keith Ohlfs

CS111, Wellesley College, Fall 1997 Announcements

[CS111 Home Page] [Syllabus] [Students] [Lecture Notes] [Assignments] [Programs] [Documentation] [Software Installation] [FAQ] [CS Dept.] [CWIS]

The due date of Exam 2 is now fixed at 6pm Sunday, November 23.

Graded Problem Sets 4 through 6 are now available outside Lyn's Office (SCI E106). Please pick them up at your earliest convenience.

Check the CS111 bulletin board often for late-breaking news about the exam.

The due date of Exam 2 has been extended to noon on Sunday, November 23.

Graded Problem Sets 5 and 6 are now available outside Lyn's Office (SCI E106). Please pick them up at your earliest convenience.

The solutions to labs 6-10 are available in the CS111 download folder in the folder named "lab_solutions". Only the .java source file and the .html files are there so you can look at the code. If you want to run them, you must add these files to a BuggleWorld project (for labs 6-8) a Turtle project (for lab9) or a KineticSculpture project (for lab10).

Exam 2 is now available. It will be due at 6pm on Saturday, November 22.

There was a review session tonight, which about 30 students attended. We talked about some of the problems in the Exam 2 Review handout. I will be happy to answer questions about these review problems throughout the examination period. In particular, I am planning another review session from 6pm-8pm on Tuesday, November 18. Watch for details.

Thus far, we have given scant coverage to iteration in lecture. You will get more practice with it in Lab#9. But you should also read about it in the following resources:

• programming.java, Section 8.1: Loops.
• Computing Concepts in Java, Chapter 6: Iteration
• On To Java, Chapter 23: How to Write Iteration Statements

The newly acquired book, On To Java (see previous announcement), also has a brief but worthwhile chapter on Recursion:

• Chapter 24: How to Write Recursive Methods.

The following books have just been added to the E101 library:

On to Java, by Patrick Henry Winston and Sundar Narasimhan. Addison-Wesley, Februrary, 1997. (3 copies)

Teach Yourself Java In Cafe' in 21 Days, by Dan Joshi, Laura Lemay, and Charles L. Perkins. Sams.net Publishing, 1996.

The Java Programming Language, by Ken Arnold and James Gosling. Addison-Wesley, 1996.

The On To Java book is of particular interest and is well worth your perusal -- that's why we've purchased three copies of it. It is arranged in short chapters focused on particular concepts or tasks. Some sample chapters that are of current interest:

• Chapter 20: How to Perform Tests Using Predicates
• Chapter 21: How to Write One-Way and Two-Way Conditional Statements
• Chapter 22: How to Combine Boolean Expressions
• Chapter 23: How to Write Iteration Statements
• Chapter 24: How to Write Recursive Methods.

Problem Set 6 is now available. It is due by 6pm on Thursday, November 13.

Please see the CS111 bulletin board for several recent messages on Problem Set 5 clarifications. It is a good idea to check the CS111 bulletin board for messages once a day!

• The problem set 5 due date has been extended to 6pm, Saturday November 8.
• There will be a recursion review session on Wednesday, November 5, from 6-8pm in SCI E111. We will work on several examples of recursion (buggles, turtles, patches). This is an excellent opportunity to get help with recursion and/or bolster your understanding. Refreshments will be served.
• The BagelBush program has been modified to include a parameter window that makes it possible to experiment with the parameters in the program without recompiling it. You can download the updated version of the program from the CS111 download folder on Nike. Be careful not to overwrite any work that you have done on the Bagel Bush program already!

Problem Set 5 is now available on the assignments page. It is due by 6pm on Friday, November 7.

The syllabus page has been updated to reflect the current status of the course, including topics covered, problem set due dates, etc. From now on will endeavor to update the syllabus page at least once a weak to keep it current.

A lot of students have asked us for stylistic guidelines for writing code in Problem Set 4. Here are some thoughts about this issue.

• Use lots of methods! Methods are named solutions to problems. Even if you only use the solution once, the fact that it is named can make your code easier to read. For instance, we recommend that your FollowWorld solution contain methods named isBagelInFront, isBagelToRight, and isBagelToLeft.
• Keep your methods small! Each method should do something very simple and understandable. As a general rule, a method should be no larger than can comfortably fit in your editor buffer. If you can't see the entire method at once, it's too big! You need to make it smaller by encapsulating some of its parts in other methods.
• Although you should make individual methods small, you should not worry about minimizing the total length of your program. We would much rather see a large and understandable program with lots of little methods than a concise but inscrutable program with only a few methods.
• Do not worry about minimizing the number of primitive operations performed by a buggle. We would rather see a clear program that performs unnecessary buggle steps than a hard-to-read program that performs fewer steps.
  
  For example, consider the following method

  public boolean isWallToRight() {
    right();
    if (isFacingWall()) {
      left();
      return true;
    } else {
      left();
      return false;
    }
  }

  Now consider some code that uses isWallToRight to walk through a "door" to the right of the buggle:

  if (isWallToRight()) {
    // Do nothing
  } else {
    right();
    forward();
  }

  The introduction of the isWallToRight abstraction introduces some inefficiencies. In particular, the buggle turns right, left, then right again when it only needs to turn right once, as in the following code:

  right();
  if (isFacingWall) {
    left();
  } else {
    forward();
  }

  However, if you always worry about minimizing such inefficiencies, you tend to end up with code that is very hard to read. In this simple case, there is not much loss of readability, but even the use of the name isWallToRight highlights something that is not emphasized in the second version of the code. As noted above, when there is a tradeoff to make, it is preferable to make the code clear than efficient -- at least in this course.

Problem Set 4 is now available on the assignments page. It is due by 11:59pm on Sunday, November 2.

Prelab 7 is now available on the assignments page. It is due before lab on Monday or Tuesday (October 27 or 28).

Prelab 6 is now available on the assignments page. It is due before lab on Monday or Tuesday (October 20 or 21).

Exam 1 has been graded and will be handed out at the end of class tomorrow. The average was 85 points out of 100. There is a histogram of the scores below. All students scoring 70 or below should make an appointment to see Lyn to talk about the exam. Anyone else who has questions about the grading of the exam should also see Lyn.

Histogram of CS111 Exam 1:

Number of students = 58

Average = 85

96-100:XXXXXXXXXXX
 91-95:XXXXXXXXXXXXXXXX
 86-90:XXXXXXXXXX
 81-85:XXX
 76-80:XXXXX
 71-75:XXXXX
 66-70:XXXX
 61-65:XX
 56-60:
 51-55:
 46-50:X
 41-45:
 36-40:
 31-35:
 26-30:
 21-25:X
 16-20:
 11-15:
  6-10:
   1-5:

Check out the solutions to Exam 1!

• An Exam 1 Review session was held tonight. We went over most of the problems from the Exam 1 Review Problems handout.
• For those who didn't make it to tonight's review session, there will be another review session on Wed, Oct 8 from 6-8pm in room SCI E111. It is strongly recommended you attend if you want extra practice with material to be tested on the exam. Refreshments will be provided to fill the tummies of those missing dinner (as well as those who are still peckish after dinner!).
• During the Exam 1 Review session, a number of bugs were found in the Exam 1 Review Problems handout from class. Please see the CS111 bulletin folder for a fix to these bugs.
• The solutions to Lab3, Lab4, and Problem Set 3 have all been posted in the cs111 download folder on Nike. Please review these as part of your preparations for the exam.

• Problem Set 1 grades have been emailed to students. The solutions to Problem Set 1 have been revised to include more comments.
• There will be Exam 1 review sessions on the evenings of Tuesday, October 7 and Wednesday, October 8. See the CS111 bulletin folder for more information.
• Hint for Problem Set 3: All four quilts can be solved by using the same break-into-four-quadrants strategy that we saw with the patchwork examples discussed in lecture. The draw16x16, draw8x8, draw4x4, etc.methods in quilts.java exhibit this strategy. Note how simple and uniform the arithmetic is in these methods. Your solutions can be just as simple; in fact, they can all use exactly the same arithmetic as draw16x16, draw8x8, etc. If you find yourself dividing by 4, 8, or 16, you're probably on the wrong track. Division by 2 is all you need.
• Suggestion for doing problem sets: I've had several complaints from students about how longthe problem sets take. In almost all cases, these complaints come from students who are working alone. I strongly recommended working with a partner or in groups! You will be pleasantly surprised at the time savings that you can achieve by working in groups. Of course, you shouldn't expect other students to solve your problems. But you can save significant time by preventing each other from exploring blind alleys.

Notes on the Java execution model are now available. You will find these helpful for PreLab #5, which is due in Lab next week.

Problem Set #3 is now available. It is due at 6pm on Tuesday, October 7. Note that this is later than the due date originally mentioned in lecture.

The default access mode for CS111 student home pages has just been modified to allow remote password access. All CS111 student pages are still accessible from all Wellesley computers as before. But now, it is also possible to access them from outside Wellesley if you use a special name/password combination. If you try to access a password-protected page from a remote computer, Netscape will prompt you for a access name and password. You should use "cs111" (without the quotes) as your access name; do not use your username as the access name! For the password, you should use the password that has been posted on the CS111 bulletin board on Lucy. (We can't post it here because this page is world readable!)

We hope that this change will make it easier for students to view and update their web pages from off-campus. Feel free to pass the cs111 password along to your family and friends, but do not post it in a public place!

The access mode fore students who requested world-readable home pages has not been changed; your web pages are still world-readable. If you would like to change them to have the password access instead, send mail to fturbak@wellesley.edu.

• Prelab #4 is now available
  
• Problem Set 2 clarifications and hints:
  • Since you have not yet had a lab on using methods, we do not require you to write any methods (other than paint) in Problem Set 2. However, we encourage you to experiment with methods on Problem Set 2 as a way to create drawings that are both more complex and more understandable than without methods.
  • Since you have had a lab on naming and arithmetic, we do expect you to use names and arithmetic in Problem Set 2. We do not expect you to name or calculate every number that you use in your program. However, it's a good idea to use name and calculations in the following situations:
    • You should name values that you consider to be parameters to your program.
    • You should use arithmetic to calculate derived values that depend on the parameters or other derived values.
    • You should name the results of arithmetic calculations that are used more than once in your program. That way you can calculate them once rather than multiple times.
  • Here's another way to think about the naming/calculation issue. How easy would it be for you to perform the following manipulations of your logo?
    • Shift every item in the logo 10 units to the right and 20 units down.
    • Make every time in the logo twice as big as it currently is.

    If you can make these modifications by tweaking just a few numbers in your program, then it is written in a robust fashion. But it making such changes requires you to carefullly examine every single number in your entire program, then you should think about adding some names and calculations.

  • A helpful hint for creating interesting visual effects: if you draw with the same color as the background color, you get the effect of "erasing" parts of an image.
    
• When turning in assignments, please check to make sure that you are turning them in
  • to the correct drop folder
  • with the correct name (as specified on the assignment description).

  We have programs that manipulate your assignment materials based on the names we have specified on the assignments. If you don't use the right names and/or drop folders, we have to hunt around for your materials. Please help us out in this regard. Thanks!

• Laura Diao is shifting her Tuesday night CS111 drop-in hours to 8pm-10pm. (They were originally 7-9pm). Please make a note of this.
  

The Font contract is now available. Both the Font contract and Color contract now have applets in them that will aid you in understanding fonts and colors.

• Important Reminder: as Stanzi mentioned in lab, you should not be using a PC-formatted disk for CS111! It turns out that the Symantec Project Manager behaves unreasonably in the presence of a PC-formatted disk. If you have a PC-formatted disk (you can tell because the disk icon says "PC"), please obtain a Mac-formatted disk and copy all your CS111 files to the Mac-formatted disk ASAP.
  
• The CS111 FAQ page has just been updated with answers to lots of recent questions about Symantec Cafe, invoking applets, and Java. Check it out when you have a question!
  
• There is now documentation for the Color contract and the Polygon contract. A Font contract will be available in the near future.

• The due date for Problem Set 2 has been extended to Monday, September 29, in order to give you sufficient exposure to the concepts needed for the assignment. Also, all instances of
  your-username-fishy.extension

  in the original problem description have been changed to

  your-username_fishy.extension

  (i.e., the hyphen has been replaced by an underscore). It turns out that Java class names may not contain hyphens, but may contain underscores.

• Documentation on how to install Symantec Cafe and the CS111 patch files is now available here. If you are not working on the machines in E101, you should install the CS111 patch files on your machine. The patch files set the preferences for Fetch and the Symantec Project Manager to be correct.

The default access mode for CS111 student home pages has just been modified to allow remote password access. All CS111 student pages are still accessible from all Wellesley computers as before. But now, it is also possible to access them from outside Wellesley if you use a special name/password combination. If you try to access a password-protected page from a remote computer, Netscape will prompt you for a access name and password. You should use "cs111" (without the quotes) as your access name; do not use your username as the access name! For the password, you should use the password that has been posted on the CS111 bulletin board on Lucy. (We can't post it here because this page is world readable!)

We hope that this change will make it easier for students to view and update their web pages from off-campus. Feel free to pass the cs111 password along to your family and friends, but do not post it in a public place!

The access mode fore students who requested world-readable home pages has not been changed; your web pages are still world-readable. If you would like to change them to have the password access instead, send mail to fturbak@wellesley.edu.

• Prelab #4 is now available
  
• Problem Set 2 clarifications and hints:
  • Since you have not yet had a lab on using methods, we do not require you to write any methods (other than paint) in Problem Set 2. However, we encourage you to experiment with methods on Problem Set 2 as a way to create drawings that are both more complex and more understandable than without methods.
  • Since you have had a lab on naming and arithmetic, we do expect you to use names and arithmetic in Problem Set 2. We do not expect you to name or calculate every number that you use in your program. However, it's a good idea to use name and calculations in the following situations:
    • You should name values that you consider to be parameters to your program.
    • You should use arithmetic to calculate derived values that depend on the parameters or other derived values.
    • You should name the results of arithmetic calculations that are used more than once in your program. That way you can calculate them once rather than multiple times.
  • Here's another way to think about the naming/calculation issue. How easy would it be for you to perform the following manipulations of your logo?
    • Shift every item in the logo 10 units to the right and 20 units down.
    • Make every time in the logo twice as big as it currently is.

    If you can make these modifications by tweaking just a few numbers in your program, then it is written in a robust fashion. But it making such changes requires you to carefullly examine every single number in your entire program, then you should think about adding some names and calculations.

  • A helpful hint for creating interesting visual effects: if you draw with the same color as the background color, you get the effect of "erasing" parts of an image.
    
• When turning in assignments, please check to make sure that you are turning them in
  • to the correct drop folder
  • with the correct name (as specified on the assignment description).

  We have programs that manipulate your assignment materials based on the names we have specified on the assignments. If you don't use the right names and/or drop folders, we have to hunt around for your materials. Please help us out in this regard. Thanks!

• Laura Diao is shifting her Tuesday night CS111 drop-in hours to 8pm-10pm. (They were originally 7-9pm). Please make a note of this.
  

The Font contract is now available. Both the Font contract and Color contract now have applets in them that will aid you in understanding fonts and colors.

• Important Reminder: as Stanzi mentioned in lab, you should not be using a PC-formatted disk for CS111! It turns out that the Symantec Project Manager behaves unreasonably in the presence of a PC-formatted disk. If you have a PC-formatted disk (you can tell because the disk icon says "PC"), please obtain a Mac-formatted disk and copy all your CS111 files to the Mac-formatted disk ASAP.
  
• The CS111 FAQ page has just been updated with answers to lots of recent questions about Symantec Cafe, invoking applets, and Java. Check it out when you have a question!
  
• There is now documentation for the Color contract and the Polygon contract. A Font contract will be available in the near future.

• The due date for Problem Set 2 has been extended to Monday, September 29, in order to give you sufficient exposure to the concepts needed for the assignment. Also, all instances of
  your-username-fishy.extension

  in the original problem description have been changed to

  your-username_fishy.extension

  (i.e., the hyphen has been replaced by an underscore). It turns out that Java class names may not contain hyphens, but may contain underscores.

• Documentation on how to install Symantec Cafe and the CS111 patch files is now available here. If you are not working on the machines in E101, you should install the CS111 patch files on your machine. The patch files set the preferences for Fetch and the Symantec Project Manager to be correct.

• CS111 drop-in tutor hours begin on Sunday, September 14. Click here for the tutor schedule and hints about making effective use of drop-in tutors.
• Purdy Ho pointed out that the PS1 Ink Inc. page handed out in class and the one on the web were slightly different. The web-based version has been updated to be consistent with the one handed out in class.

Here are some other sources of images for your web page:

Wellesley has a photofile of all students, faculty, and staff. Grab your photo from there!

Microsoft has a repository of images that you're free to put in your web pages. (Ignore the note about images only being downloadable to Windows95 systems.)

Remember, you can grab the images in Netscape by holding the mouse button down over the image, and then selecting Save Image in the resulting menu.

Pictures of CS111 students are now available for download via Fetch from Nike in the directory ~cs111/download/images. These pictures have also been collected into a student photo file. Browsing this file is a great way to learn the names of your classmates.

In order to protect the privacy of CS111 students, we have modified the CS111 class list and all students' public_html folders so that, by default, they can be read only by web browsers that are running on computers on the Wellesley campus. (All other CS111 materials can be read from any web browser in the world.) If you (1) live off-campus and need to have wider visibility for your page or (2) you are not concerned about the privacy of your pages and want to advertise them to the world, please send email to fturbak.

• Several common questions are now answered on the FAQ page. Check this page first when you have questions!
• There is now information about how to turn in prelab1 .
• Check out the new documentation describing Nike.

• There is now a class list available that includes lab and lecture schedules for each student. Make sure all your information is correct.
• PreLab #1 is now available. It is due in the first laboratory session (Sept. 8 & 9).

Note Stanzi's new office hours.

So you want to take CS111 this semester? Then click here.