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University of California, Berkeley – College of Engineering
Department of Electrical Engineering and Computer Sciences
Fall 2003 Instructors: Dan Garcia and Kathy Yelick 2003-09-
J CS6 1 B Quiz J
Personal Information Last name First Name Student ID Number The name of your TA (please circle) David Igor Ram Rishi Name of the person to your Left Name of the person to your Right All the work is my own. I had no prior knowledge of the exam contents nor will I share the contents with others in CS61B who have not taken it yet. (please sign)
Instructions
- Question 0 (-1 points if done incorrecty) involves filling in the front of this page and putting your name on every following page.
- We’ll refer to the Account class on the back page of your exam.
- In the case of all TRUE & FALSE questions, you will be graded #right – #wrong (i.e., it may be better to leave a question blank than to circle an incorrect answer).
- You have 50 minutes to complete this quiz. The quiz is open book and open notes, no computers.
- Partial credit may be given for incomplete answers, so please write down as much of the solution as you can.
- Please turn off all pagers, cell phones and beepers. Remove all hats & headphones.
Grading Results
Question Max. Pts
Points Earned
Difficulty (0=easy 5=hard)
Fairness (0=fair 5=unfair)
Total 25
Please comment above & below:
Write the difficulty and fairness ratings above and please add additional comments fl on the left here.
Question 1 : Easy Quickies… (7 points, -1 for each wrong answer… min=0)
Fill in the blanks below with the value that would be printed by the corresponding
println statment. If the program will produce a compile-time (CT) or run-time (RT)
error, fill in CT or RT. Assume previous errors have been corrected when looking at
later ones (i.e., we’re not intending any CT or RT errors to cascade).
a) int i = 1;
int j = i; i = 2; System.out.println(j); Ë _____________________
b) String s = "one";
String t = s; s = "two"; System.out.println(t); Ë _____________________
c) String s = "ABCDEF";
System.out.println (s.substring(1,5).substring(1,3)); Ë _________ System.out.println ("61".concat(s.substring(s.length()-4))); Ë ________
d) System.out.println("Perfect quiz: "); Ë Perfect quiz:
System.out.println(7+8+10); Ë ______________ System.out.println("Realistically: "+6+1+0); Ë Realistically: ________
e) public static boolean betterEquals(String w1, String w2) {
for (int i=0; i < w1.length(); i++) { if (w1.charAt(i) != w2.charAt(i)) return false; } return true; } // in main String s1 = new String("61B"); String s2 = new String("61B"); System.out.println(s1 == s2); Ë ________ System.out.println(s1.equals(s2)); Ë ________ System.out.println(betterEquals("61B","CS61B")); Ë ________ System.out.println(betterEquals("CS61B","61B")); Ë ________ System.out.println(betterEquals("61B","61B rocks")); Ë ________ System.out.println(betterEquals("61B rocks","61B")); Ë ________
f) private static void changeValues(int i, String s, Account a) {
i++; s = "B"; a.deposit(5); a = new Account(88); } // in main int score = 9; String grade = "A"; Account account = new Account(100); // …from Account class on the last page changeValues(score, grade, account); System.out.println(score); Ë ________ System.out.println(grade); Ë ________ System.out.println(account.balance()); Ë ________
We’ve staggered
the answer blanks below to give you more writing room.
b) The implementation has a representation invariant that
myAccounts.get(maxIndex) has at least as much money as any other account in
myAccounts. Your lab partner claims that your constructor provides a hole in your
abstraction that a user could exploit to break the invariant. You propose to fix the
problem by replacing Vector throughout the code by the following FixedVector
class:
public class FixedVector { private Vector myVec; public FixedVector (Vector v) { myVec = v; } public Object get(int i) { return myVec.get(i); } }
Your partner says there are still problems. Is she right? Answer Yes/No and list as
many of A-F as support it. Answer: ___________ Reasons: _______________________
No (no problems) Yes (still problems)
A) FixedVector is immutable. D) richest modifies private variables.
B) myAccounts is never returned. E) Vector (passed to FixedVector) is mutable.
C) FixedVector makes a copy of the
Vector.
F) Account is mutable
c) We would like to be able to create Accounts starting with an initial deposit in Euros
† (for this example let’s say 1 Euro † = 2 US $). We could modify the Account
class (code on the last page) by adding another constructor as so:
public Account (int euro) { this(2 * euro); } // 1 Euro=2$, so 2$ per euro
What happens when we add this constructor into our class? Circle one answer.
1) CT error because ___________________________________________________.
2) RT error because ___________________________________________________.
3) Infinite loop because the units are still euro, so it’ll call itself (with each call
doubling the input) forever.
4) It will compile and run, but it doesn’t make sense to mix dollars this way.
5) It will work fine; bring on the Euros!
d) v is a Vector whose elements, if any, are all Integers. Given the following code,
choose the answer(s) that best fits an analysis of it. Circle all that apply , and fill in
the blank(s) if appropriate.
Enumeration e = v.elements(); for (Integer i = (Integer) e.nextElement() ; e.hasMoreElements() ; i = (Integer) e.nextElement()) System.out.println(i);
The program will…
1) crash for any input.
2) never crash.
3) crash only when the input is _________________________________________.
4) print all of the elements.
5) print none of the elements.
6) print all but _____________________________________________ of the input.
Name: ______________________________________
Question 3 : How much money does my family have?… (10 points)
In Lab 2 you created a parent account (code on back page), which may itself have a
parent account, and so on. You would like to find out the total amount in all of these
accounts (including yours). You augment the Account class (on back) to add two
almost-identical recursive methods: the no-argument, non-static familyFortune and
the one-argument, static familyFortuneStatic which each return the total amount in
all of your linked family’s accounts added together. You also must show how we would
find out (from outside the class ) the family fortune starting with an Account called me.
You may only fill in 1 statement per blank (some might be empty). Each method
must be an individual solution; your non-static method may not call your static
method and vice-versa.
public _______________ familyFortune () { // non-static
if ( _______________________________________________ ) { // base case test return ( _______________________________________ ); // base case } else { return ( _______________________________________ ); // recursive case }
}
// Now, show a call to this method using the Account me (from outside Account)
____________________________me______________________________
public static ___________ familyFortuneStatic ( ________________ ) { // static
if ( _______________________________________________ ) { // base case test return ( _______________________________________ ); // base case } else { return ( _______________________________________ ); // recursive case }
}
// Now, show a call to this method using the Account me (from outside Account)
____________________________me_______________________________
