Thread: Java Final Exam - Help needed

Hi all,

I just switched my major to Information & Computer Science, so I'm completely new to Java and find programming very difficult. My final is coming up and I was wondering if any of you guys could help me answer some questions. Our professor provided us a sample final but I find it very hard to find the right answers.
I would appreciate your help.
Thanks in advance,
Jen


1. Which of the following statements about Java arrays and ArrayLists are true?

I. Arrays are similar to objects, but technically are not true objects.
II. Once an ArrayList’s size is set, it cannot be changed without reconstructing it.
III. Arrays can directly hold primitive types as well as object references.
IV. Array indexing begins at 0, but ArrayList indexing begins at 1.

A. I and III only
B. I, II and III only
C. II and III only
D. I, II and IV only
E. I, II, III and IV

2. Consider a program written using an array A of size 50. Now suppose you want to change the program so that A is an ArrayList. What changes must or should be made to the program? Your goal is to have a correctly functioning program that follows good programming practice, while minimizing changes to the code.

I. A must be constructed (using an appropriate call to the ArrayList class constructor) before any “work” with the ArrayList is attempted.
II. A call to the ArrayList’s destructor should be added, to destroy A when it is no longer needed.
III. All references to elements of A via use of an index (e.g., A[I]) must be replaced with calls to appropriate ArrayList methods.
IV. If the array stores a primitive type, the values stored in the array must be changed, either explicitly or implicitly via autoboxing, to objects.

A. I and II only D. I and IV only
B. I, III and IV only E. I, II, III and IV
C. II and III only

3. Does Java do boundary checking of arrays during program execution?

A. Yes, always
B. Yes, but only if a project file setting is made to enable such checking
C. Yes, but it is limited to single-dimension arrays
D. Yes, but only if the array is a member of a class
E. No

When answering the next four questions, use this program fragment. intObj is a class containing one private field, an integer. int getInt() returns the value of this integer; void setInt(int newValue) changes its value to newValue.

intObj p;
p = new intObj();
intObj q = new intObj();
q.setInt(20);
p.setInt(q.getInt()); //line 1
p.setInt(15);
q = p; //line 2
p = null;
System.out.print(p.getInt()); //line 3

Use these responses when answering the next two questions:

value stored where p references value stored where q references
A. 20 20
B. 15 15
C. 20 15
D. none—deference of null pointer 20
E. none—deference of null pointer none—deference of null pointer

4. What are the values stored in the locations that p and q reference after the line labeled //line 1 is executed?

5. What are the values stored in the locations that p and q reference after the line labeled //line 2 is executed?

6. What occurs when //line 3 is executed?

A. an exception is thrown
B. the number 20 prints
C. the number 15 prints
D. the number 0 prints
E. the number stored where q is referencing is printed

Consider this recursive function when answering the next 2 questions:

//intent: if n is odd and positive, returns 1 + 3 + 5 + …. + n
// if n is even and positive, returns 2 + 4 + 6 + … + n
// if n is 0 or negative, returns 0

public static long addThemUp(int n)
{ if (n > 0)
return n + addThemUp(n - 2);
else
return n;
}

7. Which of these situations would cause addThemUp to return incorrect results?

I. the parameter's value was negative
II. the parameter's value was zero
III. the parameter's value was positive and even
IV. the parameter's value was positive and odd

A. I only D. I and IV only
B. I and II only E. I, II, III and IV
C. II and III only

8. Which of these versions of addThemUp would return “as intended” results?

A. public static long addThemUp(int n) C. public static long addThemUp(int n)
{ if (n >= 0) { if (n <= 0)
return n + addThemUp(n - 2); return 0;
else else if (n == 1)
return 0; return 1;
} else
return n + addThemUp(n - 2);
}
B. public static long addThemUp(int n)
{ if (n > 0)
return n + addThemUp(n - 2);
else
return 0;
}

D. Both A and B
E. A, B and C
9. Suppose you wanted to use a function to initialize three (already declared) variables that are not fields of a class. Further suppose you are doing this in a language that allows passing parameters either by value or by reference. To initialize the variables,

A. you should pass them to the function by reference and set the values in the function; the variables will be initialized when the function returns.
B. you should pass them to the function by value and set the values in the function; the variables will be initialized when the function returns.
C. you should pass them to the function by value, set the values in the function, then return these values via a return statement.
D. define these variables so they are global to the function, then set their values within the function; that is the preferred approach.
E. you should adopt another approach: none of the above methods is a reasonable approach.

10. Here is a list of steps to be taken when a function with a parameter is called:

I. execute the function (and use the formal parameter during its execution)
II. delete the temporary storage associated with the formal parameter
III. do whatever work is necessary to determine the actual parameter‘s value
IV. do whatever work is necessary to resolve the actual parameter to a location in memory
V. create temporary storage with the name of the formal parameter
VI. copy the value of the actual parameter to the temporary storage location
VII. copy the memory location of the actual parameter to the temporary storage location

Now suppose a function is called with a parameter that is passed by reference. In order, what steps are taken to execute the function, from the start of the call through its completion, that involve this parameter? (The lists below give steps in order when read left to right.)

A. III, V, VI, I, II D. V, VI, IV, II, I
B. IV, V, VII, I, II E. IV, V, VI, II, I
C. V, VII, III, II, I

11. What is the output from the following Java program fragment?
(Reponses are on the next page.)

public static void main(String[] args)
{
int A = 10;
int B = 20;
update(A, B);
System.out.println(A + " " + B);
}

public static void update (int X, int Y)
{
X = X + Y;
Y = Y + X;
System.out.println(X + " " + Y);
}

A. None; there is a run-time error (before any output is produced)

B. 10 20 D. 30 50
10 20 10 20

C. 10 20 E. 30 50
30 50 30 50

12. Suppose you have a class MyClass and want to easily replace the contents of one object, target, with the contents of another object of MyClass, source. Which of the following statements would correctly create the copy?

A. target = source;
B. target.clone(source);
C. target = source.clone();
D. target = source.equals();
E. target = (MyClass) source.clone();

13. To enable exception handling on a block of code, one

A. encloses it in a try block
B. encloses it in a throwable block
C. labels it, then inserts that label into the Java exception handler list
D. must place the code into its own method and mark the method throwable
E. enables a trap for that code

14. In Java, what happens if code is written that could throw a checked exception in a method that has no throws clause for that exception, and there is no catch block defined in the method to handle that particular exception class?

A. If an accessible catch block exists for one of the exception’s ancestor classes, then the program compiles and runs.
B. If there is no catch block that can handle the exception, the code will not compile.
C. If the exception is thrown, and there is no catch block that can handle the exception, the program halts.
D. If the exception is thrown, and there is no catch block that can handle the exception, the program continues, but its results are unpredictable
E. Both A and B, taken together, fully describe what occurs.

15. A binary file opened for input only and relative access can

I. have its information changed
II. have its file pointer moved sequentially through the file
III. have its file pointer positioned to any object stored in the file, regardless of where the file pointer was pointing just previously
IV. be checked for end-of-line conditions

A. I and III only C. II and IV only E. I, III and IV only
B. II and III only D. I, II and IV only
Use this information when answering the next three questions:

Suppose I wanted to copy an ArrayList<string>'s contents into a file, with the string stored in a position of the ArrayList comprising one line of the file. The string in the first position of the ArrayList is to be the first line of the file, the string in the next position of the array is to be the next line of the file, and so on.

Here's an outline of what needs to be done, with two actions missing:

set current position of string array to its start;
_______________; //missing action 1
while (items remaining in the array)
{
put current position's string into the file
(followed by the new line character);
_____________; //missing action 2
}

16. Which phrase best describes what missing action 1 should be?

A. open the file as text, input, sequential access
B. open the file as text, output, sequential access
C. open the file as binary, output, relative access
D. open the file as binary, output, sequential access
E. open the file as text, input, relative access

17. Which phrase best describes what missing action 2 should be?

A. go to the next position in the ArrayList
B. go to the next line of the file (since the file pointer does not move automatically)
C. go to the next component of the file (since the file pointer does not move automatically)
D. Both A and B
E. Both A and C

18. What is the output of this program fragment? (Ignore any leading spaces.)

double X = 123.321;
String Y = "Hi!";
System.out.format("%7.3f%s", X, Y);

A. 23.32Hi! D. 1.23e2Hi!
B. 123.321Hi! E. none; a compile- or run-time error occurs
C. +23.32Hi!








19. When using hasNext() on a Scanner, how do we know when the end of file has been reached?

A. hasNext () throws an EOFException.
B. hasNext () returns a null.
C. Control transfers to the finally block associated with the block that hasNext () is in
D. Scanner() throws an EOFException.
E. hasNext () returns a false.

20. If a class is not qualified as public or private, what does that imply about its public methods and fields?

A. No other class can use them: class access defaults to private.
B. Only classes in the same file can use them.
C. Only classes in the same package can use them.
D. Only classes derived from this class can use them.
E. All classes can use them.

21. What’s the connection between public classes and .java file names? (Assume the file contains no inner classes.)

A. The file can have at most one public class; if present, it must have the same name as the file.
B. The file must have at least one public class and none of them can have the same name as the file.
C. It is common practice to name a file after one of the public classes in it, but Java does not require it.
D. If the file does not contain a public class, its name must not match the names of any of the classes in it.
E. There is no connection!

22. An interface must meet which of these restrictions?

I. It must not have any fields.
II. All methods must be abstract.
III. Only public methods are allowed.
IV. A class can implement only one interface.

A. II and III only D. I, III and IV only
B. I, II and III only E. I, II,III and IV
C. II, III and IV only









Use this information when answering the next seven questions:

Polygon is a class that defines regular polygons (figures such as equilateral triangles, squares, and regular pentagons—polygons where all the sides have the same length). It has, among other public methods, one named area(), which takes no parameters, and returns as type double the area of the polygon.

Classes Square, EqiTriangle and Pentagon are derived from Polygon. Square and EqiTriangle each have, among other public methods, one named area(), which takes no parameters and returns as type double the area of a Square and EqiTriangle, respectively. Pentagon does not define a method named area().

23. What fields does Square inherit from Polygon?

A. Only those that have public or package access
B. All except those that are private
C. Only public ones
D. All except those that have protected access
E. All of them

24. Which among the classes Square, EqiTriangle and Pentagon inherit area() from Polygon?

A. Square, EqiTriangle and Pentagon
B. Square and EqiTriangle only
C. Pentagon only
D. Square only
E. none of them

25. Define P to be a Polygon object reference, S a Square object reference and T an EqiTriangle object reference. Which of these assignment statements are legal?

I. S = T III. T = P
II. P = T IV. P = S

A. II and IV only
B. II and III only
C. II, III and IV only
D. I, II and IV only
E. I, II, III and IV

26. Suppose the object referenced in a cell of ArrayList<Polygon> pentagonGroup is of type Pentagon. If you later reference that object, what type will it have?

A. Pentagon D. Byte
B. Polygon E. Class
C. Object



27. Suppose you wish to access the pentagon stored at position 3 of an ArrayList<Pentagon> pentagonGroup and invoke the area() method on it. Which statement below does this correctly?

A. pentagonGroup.get(3).area();
B. pentagonGroup.area().get(3);
C. pentagonGroup.(Pentagon).get(3).area();
D. pentagonGroup[3].area();
E. (Pentagon)pentagonGroup[3].area();

28. Suppose you wish to call Polygon's area() method in the definition of EqiTriangle's area() method; both area() methods have the same signature. How is this done?

A. (polygon)area(); D. area();
B. super.area(); E. parent.area();
C. this.area();

29. Suppose Polygon's area() function is made abstract. Which of the following statements are then true?

I. Polygon must be made an abstract class.
II. Polygon's area function must have no body.
III. Polygon objects cannot be constructed.
IV. Any class derived from Polygon must override the area() function (if we want to be able to construct objects of those classes)

A. I and III only
B. I and II only
C. I and IV only
D. I, III and IV only
E. I, II, III and IV

30. Which of the following statements about applets are true?

I. An applet is a class that must be derived from the Java Applet class
II. An applet is invoked from HTML statements, rather than a "main()"
III. An applet almost always overrides the paint() method
IV. An applet must be compiled into a .class files before it can be used

A. I and II only
B. II and III only
C. I, II and III only
D. II, III and IV only
E. I, II, III and IV






31. When is the paint() method called?

A. Whenever the HTML of a Web page invokes it
B. Whenever the Web browser determines the screen needs to be repainted
C. Only when the user enters the page that executes the applet
D. Whenever a geometric figure is created or modified
E. Only when the applet is first invoked

32. The graphics window in Java has its origin in a specified position, and has the x and y coordinates’ values increasing in specified directions. Which of the selections below correctly gives these specifications?

origin is located x value increase y values increase

A. upper left to the right up
B. upper left to the right down
C. upper left to the left up
D. center to the right up
E. center to the right down

33. To “notice” an event (and react to it), Java requires you to do which of the following things?

I. define your own “handler” class that implements the appropriate Java-provided listener interface
II. define your own “handler” class that extends the appropriate Java-provided adapter class
III. construct an object of your “handler” class
IV. add your handler object to the list of listeners Java maintains

A. Either I or II, and III and IV
B. I, II, III and IV
C. II and III only
D. I and III only
E. Either I or II, and IV only

34. Which of the following statements about computing are true?

A. A Turing machine, a theoretical model of computing, is the most powerful computer (that works by solving problems in a step-by-step manner) yet imagined, in terms of its solving power.
B. Any problem that is computable can be solved by a program using the control structures of sequence, indefinite iteration and complete decision; no other control structures are needed
C. All digital computers could be built with just (a number of) storage devices that represent two values (say 0 and 1) and circuits that implement the logical operations AND, OR and NOT.
D. There are problems that can legally be input to a Turing machine that the machine will not be able to solve (more precisely: some problems are undecidable)
E. All of the above are true statements.

35. Which of these statements about groups of computing problems are true?

I. There are some problems that require a very long (exponential) time to solve (on a Turing machine).
II. It is unknown if P = NP.
III. If it turns out P = NP, that is of great theoretical interest, but it would have no impact on the speed of solving real-world problems.
IV. If a problem is intractable, we can solve it (on a Turing machine), but not fast enough for the solution to be useful.

A. I and III only D. I, II and IV only
B. I, II, and III only E. I, II, III and IV
C. II and IV only