Write the letter of the correct answer for each problem in the blanks on the answer form.

Transcription

1 APCS A Review Write the letter of the correct answer for each problem in the blanks on the answer form. 1. Which of the following boolean expressions evaluates to true given the boolean variables a = true, b = true and c = false. A) (a b) &&!(a && b) B) (a && c)!b C)!( (a c) && b ) D)!(a && b)!c E) (!a &&!b) c 2. Which of the following best describes the purpose of method dowhat? // precondition: num > 0 public int dowhat(int num) int total = 0; for (int loop = 2 * num; loop > 0 ; loop -= 2) total += loop; return total; A) returns num B) returns the sum of all integers between 1 and 2 * num C) returns the sum of all even integers between 0 and 2 * num D) returns the sum of all odd integers between 0 and 2 * num E) returns 0 because the loop body is never executed 3. The code segment below has an error. Object[] temp = new Object() ; System.out.println( temp[0].tostring() ); Which of the following describes the error associated with the code segment? A) The code will not compile because of an illegal declaration of variable temp. B) The code will not compile because of an illegal construction of an Object. C) The code will not compile because of an illegal call to method tostring. D) The code will compile but a NullPointerException will be thrown at runtime. E) The code will compile and display an address for the newly created object.

2 4. Given the method rec shown below, public static String rec(int num) String dig = "" + num % 2; if (num / 2 > 0) return rec(num / 2) + dig; return dig; what is the value returned by rec(25)? A) 11 B) 101 C) D) E) Which of the following statements is(are) true about ArrayLists? I. They can store only references to Objects. II. They are automatically resized when data is added to the ArrayList. III. The [ ] operator is used to access objects in the ArrayList. A) I only B) II only C) III only D) I and II only E) II and III only 6. Which of the following is the output produced by the code segment shown below? for (int num = 1; num < 10; num++) if ( (num / 2 < 3) num % 2 == 1) System.out.print(num + " "); A) 1 2 B) C) D) E) Given the code segment below, for (int index = 0; index < 5; index++) System.out.print("*"); if (index % 2 == 0) System.out.println(); System.out.println(); which of the following represents the output generated by the code segment? A) *** B) ** C) * D) * E) ** ** ** * ** *** * * ** * *

3 8. Given the code segment below, String str = "abcdef"; for (int rep = 0; rep < str.length(); rep++) System.out.print( str.substring(rep, rep + 2) ); which of the following represents the output generated by the code segment? A) abcdef B) aabbccddeeff C) abbccddeef D) abcbcdcdedef E) No output is generated because an IndexOutOfBoundsException is thrown. 9. Using the classes defined below, public class Base private int myval; public Base() myval = 0; public Base(int x) myval = x; public class Sub extends Base public Sub() super(2); which of the following statements will compile without error? I. Base b1 = new Base(); II. Base b2 = new Sub(); III. Sub s1 = new Base(5); A) I only B) II only C) III only D) I and II only E) I, II and III 10. Using the method search and the declaration for arr shown below, what will be returned by the call search(arr, 6)? int[] arr = 2, 3, 5, 6, 8, 12; public static int search(int[] list, int key) for (int loop = 0; loop < list.length; loop++) if (list[loop] == key) return loop; return -1; A) -1 B) 1 C) 2 D) 3 E) 6

4 11. Assume the following class definitions have been made. public class A private int a; public A() a = 2; S.display(a); public class B extends A private int b; public B(int val) b = val; S.display(b); public class C extends B private int c; public C(int val1, int val2) super(val2); c = val1; S.display(c); public class S public static void display(int num) System.out.print( num ); Which of the following output is produced by the declaration C cref = new C(3, 5)? A) 235 B) 253 C) 35 D) 532 E) Given the methods below, // graphically displays a line from point (x, y) to point (x2, y2), where // the coordinate system has (0,0) at the top left corner, larger x values // are to the right of smaller x values, and larger y values are below // smaller y values public void drawsegment(int x, int y, int x2, int y2) /* <... implementation not shown...> */ public void line(int max) for (int pos = 0; pos <= max; pos++) drawsegment(0, pos, pos, 0); choose the best representation of the graphical output that would be generated by a call to line(50). A) B) C) D) E)

5 13. Given the incomplete method minval, which of the following could be used to replace <... missing boolean expression...> and <... missing code...> so that minval works as intended? // returns the smallest value in the ArrayList arrlist. public static Integer minval(arraylist arrlist) int loc = 0; Integer small = (Integer) arrlist.get(loc); for (int pass = 1; pass < arrlist.size(); pass++) Integer temp = (Integer) arrlist.get(pass); if ( <... missing boolean expression...> ) <... missing code...> return small; <... missing boolean expression...> <... missing code...> A) temp.compareto( small ) < 0 small = temp; loc = pass; B) temp.compareto( small ) < 0 temp = temp; pass = loc; C) temp.compareto( small ) == 0 small = temp; loc = pass; D) temp.compareto( small ) > 0 small = temp; loc = pass; E) temp.compareto( small ) > 0 temp = small; pass = loc; 14. Given the following code segment, A) ECA String str = "ABCDE"; int len = str.length(); for (int sub = len - 1; sub >= 0; sub = sub - 2) str += str.substring(sub, sub+1); B) ABCDE what is the value of str when the code segment has finished executing? C) ABCDEECA D) ABCDEABCDE E) ABCDEEDCBA

6 15. Given the method isoper and the partially completed method opercount, which code segment could be substituted for <missing code> so opercount would return the number of occurrences of "+" and "-" stored in the String expression? boolean isoper(string str) // <... implementation not shown...> // returns true if str is an arithmetic operation "+" or "-" // returns false otherwise int opercount(string expression) int counter = 0; for (int loop = 0; loop < expression.length(); loop++) if ( <missing code> ) counter++; return counter; A) expression == "+" expression == "-" B) expression.substring(loop, loop+1) == "+" expression.substring(loop, loop+1) == "-" C) isoper( expression ) D) isoper( expression.substring(loop, loop+1) ) E) isoper( "+" "-" ) 16. Which of the following object oriented programming concepts helps to minimize the amount of code needed for the creation of new classes that are related to previously defined classes? I. Encapsulation II. Inheritance III. Polymorphism A) I only B) II only C) III only D) I and III only E) I, II and III

7 17. Which of the following statements are true about an ArrayList? I. They can hold both primitive types and Objects. II. They are automatically resized when the add method is called. III. The [] operator is used to access objects in the ArrayList. A) I only B) II only C) III only D) I and II E) I, II and III 18. Using the classes defined below, class Base public void methodone() System.out.print("B1"); class Sub extends Base public void methodone() super.methodone(); System.out.print("S1"); what is the output produced by the following code segment? Base s = new Sub(); s.methodone(); A) B1 B) S1 C) B1S1 D) S1B1 E) No output is generated because a ClassCastException is thrown. Use the method rec, defined below, to answer questions 6 and 7. public static int rec(int val) if (val < 2) return 1; return val + rec(val / 2); 19. How many times is rec called when calculating rec(15), including the call to rec(15) itself? A) 1 B) 2 C) 3 D) 4 E) What is the value returned by rec(15)? A) 1 B) 15 C) 22 D) 25 E) 26

8 21. Which of the following is the best reason for using inheritance when writing code? A) Inheritance restricts the use of polymorphism, therefore making code more readable. B) Encapsulation can only be implemented through the use of inheritance. C) The amount of code, and therefore the amount of bugs, produced in a program can be effectively reduced through the use of inheritance hierarchies. D) Overloading methods in sub classes found in inheritance hierarchies reduces errors that would otherwise be introduced through method overriding. E) The use of super classes improves the effectiveness of your code by increasing the number of methods that can be defined in a class. 22. Given the incomplete method maxloc, which of the following could be used to replace <... missing code...> so that maxloc works as intended? // returns the location of the largest value in the array arr. public int maxloc(int[] arr) int loc = 0; for (int pass = 1; pass < arr.length; pass++) if ( arr[pass] > arr[loc] ) <... missing code...> return loc; A) return arr; B) arr[loc] = pass; C) return arr[loc]; D) loc = pass; E) arr[pass] = arr[loc]; 23. Which of the following is the output produced by the code segment shown below? for (int num = 1; num < 10; num++) if ( (num / 2 < 3) num % 2 == 1) System.out.print(num + " "); A) 1 2 B) C) D) E)

9 24. The code segment below has an error. Object[] temp = new Object() ; System.out.println( temp[1].tostring() ); Which of the following describes the error associated with the code segment? A) The code will not compile because of an illegal declaration of variable temp. B) The code will not compile because of an illegal construction of an Object. C) The code will not compile because of an illegal call to method tostring. D) The code will compile but a NullPointerException will be thrown at runtime. E) The code will compile but an ArrayIndexOutOfBoundsException will be thrown at runtime. 25. Which of the following statements are true about an ArrayList? I. They use a static final field to store the length of the list. II. They are automatically resized when the index exceeds the length of the list. III. The [ ] operator is used to access objects in the array. A) I only B) II only C) III only D) I and III only E) I, II and III

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