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Reviewing for the AP Computer Science A Exam

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So today, I went to my last AP Computer Science review session via the grant. We went over some sample multiple choice for the one session I attended out of four (I also had AP Calculus and AP Statistics today), and Mr. Billington (the speaker from TJ Governor's School in Northern Virginia) passed out a breakdown of the Multiple Choice Questions. So before we get to the multiple choice topics, here is what I would emphasize knowing for the AP Computer Science Exam. Know:
-Inheritance (class Sub extends Base, super vs. this)
-Polymorphism (Method overloading & overriding, dynamic method binding)
-Interfaces and Abstract classes
-ArrayLists and the List interface
-GridWorld, specifically the Critter class
-Recursion (if you see the method named mystery(), chances are that it is a recursion question)

After looking through the Multiple Choice Breakdown, additional topics that the AP likes to hit on are:
-String class, specifically substring()
-Searching and Sorting
-Boolean algebra
-Logic flow (be able to follow loops, conditionals, etc.)
-Comparable and .equals()

-More on Searching and Sorting: On the AP Exam, the only direct searching and sorting question they may ask is something like "Which is more efficient: binary or linear search?" or "Rank the following in terms of greatest to least efficient: Mergesort, Selection Sort, Insertion Sort." However, the algorithms I have just mentioned as well as a couple others will appear conceptually in the multiple choice. By this, I mean that certain questions will have code that is based off the concepts or parts of each algorithm. Today when we went over multiple choice, I saw two or three questions that beat around the bush of Bubblesort.

-GridWorld accounts for 25% of the Free Response (1 out of 4 FRQs), and 12.5% of the Multiple Choice. So without it, you have to get everything else perfectly to get a 5. Otherwise, you are starting at a 4. If you do nothing else, go over GridWorld before the AP Exam.

-Breakdown of the AP Exam: The AP Computer Science A Exam is 3 hours in length. You will have 90 minutes to complete 40 multiple choice, which accounts for half of your composite score; and 90 minutes to complete four FRQs, which account for the other half of your composite score. In my class, we obliterate the FRQs. This, however, is not the case for most students. The FRQs are probably what you will be stressed for time on, so work efficiently, but carefully. Do not worry about commenting your code. Also, your solution does not have to be entirely correct for you to get full credit. That's right- you can have a wrong solution and still get full credit. The AP graders (who by the way, are not all that well versed in Java or programming) use the AP rubrics to look through your code. Things like defining the method header, attempting to invoke a super call, and having a correct return statement will get you points. The big don't on the FRQs, though, is to not rewrite code. If you are supposed to write a method in part A, and you don't know how, you can still assume it works as intended in part B and invoke it. In fact, this is what the AP graders are looking for.

Composite Scores: The AP Computer Science Exam, in the tradition of the AP, is graded on a 5 point scale, with 5 being Extremely Well Qualified, and 1 being Very Unqualified. The AP exams are all graded using Normal Distributions, so the grades are distributed based on how everyone who takes the exam on a particular year does. If you want to estimate what you would get on sample AP exams, here is the breakdown for CS for the number grade followed by the composite score range:
5: 60-80
4: 44-59
3: 33-43
2: 25-32
1: 0-24

Now let's calculate the composite scores:
Multiple Choice = (Number Correct - .25(Number Wrong))
Free Response = (Total FRQ Points (out of 36) * 1.11, do not round)
Composite Score = MC + FRQ, rounded to the nearest whole number

So to put yourself in 5 range, you want to be scoring at least 7/9 on each FRQ and 30 points (not necessarily 30 correct) on the Multiple Choice.

Formula Sheets on the AP: So if you are in other AP Math or Science classes like Statistics, Chemistry or Physics, you get a formula sheet on the AP Exam. Computer Science is no different. However, rather than having mathematical formulas, we get an API with the AP subset. Some of the classes included are Object, String, ArrayList, Math, and the major classes in the GridWorld library. You even get the code for some of the GridWorld classes. I believe Critter is one of these classes, along with Actor and Bug. For other components like the Grid interface and Location class, you get only the method headers, fields, and brief descriptions of both. So if you are absolutely lost, read the API.

3 Comments On This Entry

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24 April 2010 - 06:33 PM
I cannot emphasize the true importance of knowing Grid World inside and out. I know my Java (as seen through my Expertship), however, we barely went over Grid World and the first time I saw the Documents on it was at the test. I scraped by with a 4, whereas I could have potentially scored a 5. I was not with DIC at the time, and so it proved to be a lose-lose situation.

Case in point? Study Grid World.


25 April 2010 - 03:24 PM
I completely agree with Dogstopper here. If you do not get all your points on the FRQs and the MC and skip the GridWorld sections, the highest you can get is a 4.

@Dogstopper: You can retake the AP CS exam this year or next to get a 5.


28 April 2010 - 06:21 PM
Ooh sweet! I might do that!
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