Fall CS302 2006: Practice Exam 1
1. Assume that x, y, and z are all int variables. Consider the following code segment: if (x == 0) { if (y == 1) z += 2; } else { z += 4; } System.out.print(z); What is printed if x, y, and z are all equal to zero before the code segment executes? A. 0 B. 1 C. 2 D. 4 E. 6 2. Assume that the following variable declarations have been made. int j, k; double d1, d2; boolean b; Which of the following statements would not compile? A. j += k * 2; B. d1 = (double)k/d2; C. j = k * b; D. b = !b; E. b = (j == k); 3. Which of the following best describes the circumstances under which the expression !(a && b) && (a || b) evaluates to true? A. Always B. Never C. Whenever both a and b are true D. Whenever neither a nor b is true E. Whenever exactly one of a and b is true 1
2
Questions 4 and 5 concern the following Animal class. public class Animal { private String name; private double age; // constructor public Animal( String n ) { name = n; age = 0.0; } public String getName() { return name; } public double getAge() { return age; } public void setAge(double a) { age = a; } }
4. Consider the following incomplete method. public void doSomething() { Animal s = new Animal("Spot"); <missing statements> } Assume that method doSomething is not part of the Animal class. Which of the following statements could be used to replace <missing statements> so that the code would compile? A. s.setAge(100); System.out.println(s.getAge()); B. s.age = 100; System.out.println(s.age); C. s.setAge(age + 1); System.out.println(s.getAge()); D. s.age = 95.5; System.out.println(s.age); E. s.setAge(95.5); System.out.println(s.setAge()); 5. Consider changing the Animal class so that both the name and the age of an animal can be set when an Animal object is created. For example: Animal an1 = new Animal("Spot", 10.0); Animal an2 = new Animal("Rover" 25.5); // Spot's age is 10.0 // Rover's age is 25.5
Which of the following best describes the change that should be made? A. Define a constructor with no arguments. B. Define a constructor with one argument. C. Define a constructor with two arguments. D. Define a method named setNameAndAge. E. It is not possible to change the Animal class as specified.
3
6. Consider the following code segment: int x = 0; boolean y = true; if (y && (x != 0) && (2/x == 0)) System.out.println("success"); else System.out.println("failure"); Which of the following statements about this code segment is true? A. There will be an error when the code is compiled because the first && operator is applied to a nonboolean expression. B. There will be an error when the code is compiled because a boolean variable (y) and an int variable (x) appear in the same if-statement condition. C. There will be an error when the code is executed because of an attempt to divide by zero. D. The code will compile and execute without error; the output will be "success." E. The code will compile and execute without error; the output will be "failure." 7. Assume that x is an initialized int variable. The code segment if (x > 5) x *= 2; if (x > 10) x = 0; is equivalent to which of the following code segments? A. x = 0; B. if (x > 5) x = 0; C. if (x > 5) x *= 2; D. if (x > 5) x = 0; else x *= 2; E. if (x > 5) x *= 2; else if (x > 10) x = 0; 8. Consider the following code segment: String s1 = "abc"; String s2 = s1; String s3 = s2; After this code executes, which of the following expressions would evaluate to true? I. s1.equals(s3) II. s1 == s2 III. s1 == s3 A. I only B. II only C. III only D. I and II only E. I, II, and III
4
9. Consider writing a method whose sole purpose is to write an error message using System.out.print. Which of the following best characterizes the choice between making the method's return type void and making it String? A. The return type should be void because the method performs an operation and does not compute a value. B. The return type should be void because that is the default return type for Java methods. C. The return type should be String because the method is not a constructor. D. The return type should be String because the method prints a string. E. If the method is a public method then its return type should be String; otherwise, it should be void. 10. A program is being written by a team of programmers. One programmer is implementing a class called Employee; another programmer is writing code that will use the Employee class. Which of the following aspects of the public methods of the Employee class does not need to be known by both programmers? A. The methods' names B. The methods' return types C. What the methods do D. How the methods are implemented E. The numbers and types of the methods' parameters
5
11. Consider the following incomplete definition of the Time class. A Time object represents the amount of time needed to complete some task (for example, 1 hour and 40 minutes). public class Time { private int hours; // 0 <= hours private int minutes; // 0 <= minutes <= 59 // constructor not shown public boolean shorterTime(Time other) { // returns true if this time represents a shorter amount of time // than other <missing code> } // other methods not shown } Assume that the hours field is never negative, and the minutes field is always between 0 and 59. Which of the following can be used to replace <missing code> in the body of the shorterTime method to correctly complete that method? A. if (hours < other.hours) return true; return false; B. if (hours < other.hours && minutes < other.minutes) return true; return false; C. if (hours < other.hours || minutes < other.minutes) return true; return false; D. if (hours < other.hours) return true; if (hours > other.hours) return false; if (minutes < other.minutes) return true; return false; E. if (hours < other.hours) return true; if (minutes < other.minutes) return true; if (hours > other.hours) return false; return false;
6
Questions 12 and 13 refer to the following Location class. public class Location { private String name; private double latitude; private double longitude; // constructor public Location(String n, double lat, double lon) { name = n; latitude = lat; longitude = lon; } public String getName() { return name; } public void setName(String n) { name = n; } public boolean equals(Location other) { return ((latitude == other.latitude) && (longitude == other.longitude)); } }
12. Assume that variables L1, L2, and L3 have been declared and initialized as follows. Location L1 = new Location("Baltimore", 39.18, 76.38); Location L2 = new Location("Baltimore", 39.18, 76.38); Location L3 = new Location("Albany", 39.18, 76.38); Which of the following expressions evaluate to true? I. II. III. L1.equals(L2) L2.equals(L3) L1 == L2
A. I only B. II only C. III only D. I and II E. I and III
7
13. Consider the following code segment. Location = L1 new Location("Baltimore", 39.18, 76.38); Location L2 = L1; Location L3 = L1; L1.setName("NewYork"); L2.setName("Chicago"); System.out.print(L1.getName() + " " + L2.getName() + " " + L3.getName()); What is printed when the code executes? A. NewYork NewYork NewYork B. Chicago Chicago Chicago C. NewYork Chicago Baltimore D. Chicago Chicago Baltimore E. NewYork Chicago Baltimore 14. Consider the following (incomplete) method: public void change( double value ) { ... } Assume that variable k is an int, that variable s is a String, and that variable d is a double. Which of the following calls to method change will compile without error? Call I change( k ); A. I only B. II only C. III only D. I and II E. I and III 15. If addition had higher precedence than multiplication, then the value of the expression 2 * 3 + 4 * 5 would be which of the following? A. 14 B. 26 C. 50 D. 70 E. 120 Call II change( s ); Call III change( d );
8
16. Assume that a method called checkStr has been written to determine whether a string is the same forwards and backwards. The following two sets of data are being considered to be used to test method checkStr: Data Set 1 Data Set 2
"aba" "?" "z&*&z" "##"
"abba" "abab"
Which of the following is an advantage of Data Set 2 over Data Set 1? A. All strings in Data Set 2 have the same number of characters. B. Data Set 2 contains a string for which method checkStr should return false, as well as a string for which method checkStr should return true. C. The strings in Data Set 2 contain only lowercase letters. D. Data Set 2 contains fewer values than Data Set 1. E. Data Set 2 has no advantage over Data Set 1. 17. Which of the following statements about Java variables and parameters is true? A. A variable must be declared before it is used. B. The same variable name cannot be used in two different methods. C. Variables declared to be of type int must be named i, j, or k. D. It is good programming practice to use single letters as the names of all variables. E. It is good programming practice to name formal parameters param1, param2, and so on, so that it is clear where they appear in the method's list of parameters. 18. Which of the following is not an example of a good use of comments? A. Comments included at the beginning of a method to say what the method does. B. Comments included at the end of every line of a method to explain what that line of code does C. Comments included at the beginning of a method to say which of the class's fields are modified by that method D. Comments included in a class's constructor to explain how the class object is initialized E. Comments included at the beginning of a class definition to say what the class represents and what operations it provides.
9
Questions 19 and 20 refer to the following code segment (line numbers are included for reference). Assume that method readInt reads and returns one integer value. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. int x, sum; x = -1; sum = 1; x = readInt(); if (x > 0) { sum += x; } x = readInt(); if (x > 0) { sum += x; } x = readInt(); if (x > 0) { sum += x; } System.out.println(sum);
19. For the purposes of this question, two code segments are considered to be equivalent if, when they are run using the same input, they produce the same output. Which line(s) could be removed from the code segment given above so that the resulting code segment is equivalent to the original one? A. Line 2 B. Line 3 C. Line 4 D. Line 6 E. Lines 9 and 11 20. The code segment given above was intended to read three values and then to print the sum of the positive values read. However, the code does not work as intended. Which of the following best describes the error? A. Variable x is not initialized correctly. B. Variable sum is not initialized correctly. C. Variable x is used before being initialized. D. Variable sum is used before being initialized. E. The code does not prevent non-positive values from being included in the sum.
10
21. Consider the following data field and method (which are both part of some class). private String word; public boolean findWord( String bigWord ) { int index = bigWord.indexOf( word ); return ( (index > 0) && (index + word.length() < bigWord.length()) ); } For which of the following values of bigWord and word will method findWord return true? bigWord A. B. C. D. E. hello spicey apple palid palid word he ice ape aid lid
11
Question 1
Consider the partially defined Person class below. public class Person { private String firstName; private String lastName; // constructor not shown public void printName() { /* part (a) */ } public boolean comesBefore(Person other) { /* part (b) /* } } Part (a) Write method printName, which should print the last name of the person followed by a comma, then the first initial, then a period, then a newline. For example, if the person's first name is Sandy and the last name is Jones, method printName should print Jones,S. Complete method printName below. public void printName() {
12
Part (b) Write method comesBefore. Method comesBefore should return true if the person's name would come before other's name in the phone book (i.e., the person's last name comes first in alphabetical order, or the two last names are the same, and the person's first name comes first in alphabetical order); otherwise, method comesBefore should return false. For example, assume that variable P represents a person whose name is Sandy Jones. The table below shows the results of some calls to comesBefore. other.firstName Aaron Martha Amy Wendall other.lastName Copland Washington Jones Jones Result of the call P.comesBefore(other) false true false true
In writing method comesBefore, you may use the compareTo method of the String class. If you have String variables named s and other, the call s.compareTo(other) returns a negative integer if the string represented by s comes before the string represented by other in alphabetical order; it returns zero if the two strings are the same, and it returns a positive integer if the string represented by s comes after the string represented by other. Complete method comesBefore below. public boolean comesBefore(Person other) {
13
Question 2
A laundry uses a Java program to keep track of its customers and their orders. A class called LaundryOrder will be used to keep track of an individual order. Each LaundryOrder object will need to include the following information: The name of the customer The number of items to be cleaned Whether the order is ready The LaundryOrder class must provide the following operations:
Create a LaundryOrder object given a customer name and number of items. Access the customer name, the number of items, and whether the order is ready. Change the object to show that the order is ready. Write a complete definition of the LaundryOrder class below, including field declarations, a constructor, and all of the required methods.