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Material Type: Exam; Class: Object-Oriented Programming and Data Structures; Subject: Computer Science; University: Cornell University; Term: Fall 2005;
Typology: Exams
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NetID______________
Closed book; closed notes; no calculators. Write your name and netID above. Write your name clearly on each page of this exam. For partial credit, you must show your work.
Do not begin until you are instructed to do so. You have 90 minutes.
a) T F The statement “String s;” calls the constructor of class Object.
b) T F The protected modifier signifies that the method or variable can only be accessed from within its class, from within its subclasses, or from within classes in the same package.
c) T F In Java, a class may directly inherit from more than one abstract class.
d) T F If class A inherits from abstract class B, and B implements an interface C, then a cast from an object of type A to an object of type C will always succeed. Example: A a; ... C c = (C) a;
e) T F In Java, an interface can extend multiple interfaces.
f) T F Strong induction is much better than weak induction, and therefore we should use it whenever possible.
g) T F In Java, objects are stored in the stack frames.
h) T F If a variable is declared to hold a primitive type then its static and dynamic types are always the same.
i) T F During a Java program’s execution, a single method can correspond to multiple stack frames.
j) T F Any binary tree of depth 2 has ≤ 7 nodes.
class ListCell { public Object datum; // Data for this cell public ListCell next; // Next cell }
ListCell removeEven (ListCell list) { if (list == null) return null; if (list.next == null) return null; list.next.next = removeEven(list.next.next) return list.next; }
4. ( Types; 24 points; 3 each ) Consider the following interface and class declarations.
interface I1 {...} interface I2 {...} interface I3 extends I1 {...} class C1 implements I1 {...} class C2 implements I2 {...} class C3 implements I3 {...} class C4 extends C3 implements I2 {...}
For each of the following snippets of Java code, determine whether the code will produce no error, a run-time error, or a compile-time error. (Assume that each snippet is tested independently of the others.)
a) I2 a = new I2(); Compile Error
b) I2 b = new C2(); OK
c) C3 c = new C4(); OK
d) C2 d = new C4(); Compile Error
e) C4 e = new C3(); Compile Error
f) C4 f = (C4)(new C3()); Runtime Error
g) I1 g1 = new C1(); OK C4 g2 = new C4(); g1 = g2;
h) I1 g1 = new C4(); Compile Error I2 g2 = new C2(); g2 = g1;
java MainProblem hello
Output: hello ello llo lo o
Specifications:
Hint: You are likely to find the substring method of class String to be useful. Here is its documentation from the Java API.
String substring(int beginIndex) Returns a new string that is a substring of this string. String substring(int beginIndex, int endIndex) Returns a new string that is a substring of this string.
public class MainProblem {
public static void main (String[] args) {
if (args[0].length() == 0)
System.out.println();
else {
System.out.print(args[0] + " ");
args[0] = args[0].substring(1);
main(args);
}
} }
Bonus Point Questions
Work on these only if you have extra time. Bonus points are not used in determining your final course grade unless you are on a grading borderline.
B1. What is the answer to this question? ???
B2. Consider the following two classes. What is printed when the main method is executed? (You will probably need to mark off lengths on a straightedge to distinguish between variables. You can tear off a scrap of paper from the last page for this purpose, but we still want your course feedback and the feedback is worth 5 bonus points.)
public class __________ { static int _________; public static void main(String[] ___________) { ________ ________ = new ________( (new ________(++__________._________)).________ ); ________(________.________(________.________)); ________(________.________(________).________); ________(________(________.________(________))); } // method main static int ________(________ ________) {return ________.________;} public static void ________(int ________) {System.out.println(________);} } // class __________
class ________ { int ________; ________(int ________) { this(________,________++); this.________=________; } ________(int ________, int _________) { this.________+=_________+=this.________+________++; } int ________(int ________) { ________(this); return ________; } ________ ________(________ ________) { ________.________+=++__________._________; return new ________(________.________); } } // class ________
Prints: 3 9 13 ( on separate lines)
