1.00/1.001 Introduction to Computers and Engineering Problem Solving Fall 2002

Transcription

1 1.00/1.001 Introduction to Computers and Engineering Problem Solving Fall 2002 Name: TA s Name: Tutorial: For Graders Question 1 Question 2 Question 3 Question 4 Question 5 Total

2 Problem 1 (10 Points). Circle or for each of the following statements about static variables in Java. A. A static data member of a class must be declared using a primitive type. B. A static data member of a class is not associated with any particular instance of the class. C. A static data member of a class cannot be accessed outside the class. D. A static data member of a class must be initialized in a class constructor. E. A static data member of a class cannot be changed after it is initialized.

3 Problem 2 ( Points). Consider the following class definition: public class Borg { static int nextid = 0; int borgid; public Borg() { /* assign unique id */ XXX We want to give each Borg object a unique identifier. Which of the following lines could be used in place of the XXX to assign a unique id to each Borg object? (Circle only ONE choice) a) nextid = borgid++; b) borgid += 1; c) borgid = nextid + 1; d) borgid = ++nextid; e) borgid += nextid;

4 Problem 3 (45 Points). The following main method uses the functions print and add to produce this output: Output: Array a is: Array b is: 7 3 Array c is: 11 Main Method: public static void main (String args[ ]) { int a[] = {1,3,5; int b[] = {7,,3; System.out.println("Array a is: "); print(a); System.out.println("Array b is: "); print(b); int c[] = add(a, b); System.out.println("Array c is: "); print(c); Provide implementations for print and add so that the main method produces the correct output (see next page).

5 A. Write code for correctly printing a single array. public static void print(int [] a) { //WRITE CODE HERE for(int i = 0; i < a.length; i++) { System.out.println(a[i]; B. Write code for adding the elements of two int arrays. The result should be returned as a new array: Assume that the arrays, a and b, have the same number of elements. public static int[] add(int[] a, int[] b) { //WRITE CODE HERE int[] c = new int[a.length]; for(int i = 0; i <a.length; i++) c[i] = a[i] + b[i]; return c; When writing these functions remember that the output of main must match: Array a is: Array b is: 7 3 Array c is: 11

6 Problem 4 (25 Points). Here is a class that has two instance fields: type and weight. public class Cookie { // type of cookie: Chocolate, Oatmeal, Raisin, String type; // weight of cookie in grams: 2.9, 3.4, double weight; // rest of class Provide a constructor for this class. This constructor should take two arguments: a String and a double. This will allow a programmer to create a new Cookie object with parameters like Chocolate and 2.9 public Cookie(String ctype, double cweight) { type = ctype; weight = cweight; Provide another constructor for this class. This constructor should take a single String as an argument. This will allow a programmer to create a new Cookie object with a parameter like Chocolate. When no weight is provided, the Cookie should weigh 2 grams. public Cookie(String ctype) { type = ctype; weight = 2.0;

7 Problem 5 (12 Points). public class SecretCode { public int publickey; private int secretkey; private SecretCode(int pkey, int skey) { publickey = pkey; secretkey = skey; public static void main(string[] args) { SecretCode code = new SecretCode(535979, ); UserAccount acct = new UserAccount("beaver", "timmit"); A B C D System.out.println("code's public key is " +code.publickey); System.out.println("code's secret key is " +code.secretkey); System.out.println("acct's username is " + acct.username); System.out.println("acct's password is " + acct.password); A B C D System.exit(0); class UserAccount { public String username; private String password; public UserAccount(String u, String p) { username = u; password = p; Consider the program above, which consists of two classes that are contained in the same file. Circle or for the following statements. a. The line at A will compile and run. b. The line at B will compile and run.

8 c. The line at C will compile and run. d. The line at D will compile and run.