Download Spring 2007, Wednesday, 2/7/07

CS 240 Exam 1
Page 1
Computer Science II
Spring 2007, Wednesday, 2/7/07
100 points
Name _____________________________
2/7/07
Explain or give the UNIX or vi commands or keystrokes to do the following tasks.
[28 pts]
1. Display all filenames (including hidden ones) found in your current directory. __________________[2]
2. Display java source files found in your subdirectory cs2 _______________________________ [2]
3. Create a subdirectory in your home directory called projects. ___________________________[2]
4. Move all .java files in your home directory to this subdirectory projects ________________________[2]
5. Delete all files that contain tmp anywhere in the name from your home directory. ____________________[2]
6. Change your current working directory up to the parent directory ________________________[1]
7. Display only the last 10 lines of the file test.java . ______________________[2]
8. Begin capturing the screen display to a file for printing later. ____________________ [1]
9. Start the visual editor on file test.java ______________________[2]
10. Compile the code in test.java ____________________________[2]
11. What keystroke designates end of input in Unix? ____
What keystroke cancels a program in Unix? ____
What character designates the current directory? _____
What keystroke erases the current input line? _____ [4]
12. Print your typescript file, 2 pages per sheet. _________________________ [1]
13. Run the Java program first using the filename mydata as a command line argument.
__________________________________________________ [2]
14. Run the Unix program filter redirecting the file data for input and sorts output stream. Just displays results.
__________________________________________________ [3]
15. Give the keystroke(s) in vi to perform the following actions
[8 pts]
_____ move the cursor down 1 line (1 character)
_____undo the previous action (1 char)
_____ delete the current character (1 char)
_____ start insertion mode (1 char)
_____ end insert mode (1 char)
_____ delete the current line (2 chars)
_____ exit and do not save the file or its changes (3 chars)
_____exit and save the file (2 chars)
CS 240 Exam 1
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16. Arrays.
[7 pts]
a. Give a Java code segment to define an integer array nums of size elements and use a for loop to initialize
each element to its index (element 0 contains a 0, element 9 contains a 9, etc.). [4]
b. List the steps to make a filled array larger. [3]
17. Abstract Data Types. (True/False)
[5 pts]
a. ____ An ADT defines the data organization, its operations as well as the implementation.
b. ____ All ADTs implemented as Java classes ultimately inherit from the Object class.
c. ____ An abstract class can be used to define shared methods and instance variables inheritable by related
subclasses.
d. ____ An interface is another name for an abstract class.
e. ____ ADT specifications depend on the implementation language, e.g. Java.
18. Object-oriented programming design principles.
[6 pts]
a. The Information Hiding Principle specifies that the implementer of a module is provided only the
necessary information to _______________ the module and that the ______________ is provided
only the necessary information to use the module.
b. A ________-condition specifies what must be true about the inputs at the beginning of a method and a
____________________ specifies what must be true at the end of a method, if the _______-condition
holds. These assertions provide a form of a contract between the ____________ and the implementer.
CS 240 Exam 1
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19. Miscellaneous Java concepts (True/False)
[10 pts]
a. _____ Each Java class should be defined in its own separate file with the extension .java and that file name
must match the class name.
b _____ The contents of the .class file are called bytecodes, which are dependent on a particular machine.
c. _____ Garbage collection in Java is the automatic recovery of memory from inaccessible objects.
d. _____ The toString method that should be defined for each class is an example of an accessor.
e. _____ The toString method is an example of a method that is inherited but can be overridden.
f. _____ Two strings compared by the compareTo() results in an integer..
g. _____ An iterator ensures that all elements of a collection can be accessed in some order.
h. _____ The class that extends an existing class is called the superclass.
i. _____ The primitive types of int and double are examples where the variable refers or points to the value.
j. _____Reusability is a quality software goal in object-oriented class design.
20. Number the steps of the software development cycle (Waterfall method) from 1 to 6 in correct order.
[5 pts]
_____ Testing
_____ Maintenance
_____ Design
_____ Requirements identification
_____ Analysis
_____ Implementation
21. Rank the algorithm complexities from "fastest" to "slowest" (increasing dominance). 1 is fastest (good, low
cost) and 6 is slowest (bad, high cost).
[5 pts]
O(2n)
O(n)
O(n2)
O(log n)
O(1)
O(n2 log n)
22. For each of the cost functions below give the “best” big-O equivalence where n is the data set size and k is
some constant not related to the size of data.
[8 pts]
_______ f(n) = 2n3 + 9n2 + 50n + 100
_______ f(n) = 17 + kn + 5n2
_______ f(n) = kn + 4k4
_______ f(n) = 8n8 +2n
CS 240 Exam 1
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23. Estimate the running times using the big-O notation for each of these code segments. The size of the data set
is n. Assume all variables are integer.
[8 pts]
____________
____________
____________
____________
for(j=n; j>0; j--){
// 3 assignments
}
for (i=1; i<=n; i++)
for(j=1; j<=n; j++)
for(k=i; k<=n; k++){
// 4 assignment and 2 i/o statements
}
i = 1000;
while(i>0){
if(i % 2 == 1){ // if i is odd
for(j=i; j<=n; j++){
foo(j,n); //foo executes in quadratic time
}
// 3 assignment statements
i = i-1;
}
for (k=n; k>0; k--){
j=0;
while (j<100){
bar(j,n); //bar executes in linear time
j=j+1;
}
}
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21. Below is a segment of code similar from the text and your project. Assume Date is a class that holds the day,
month and year along with a String description. A constructor can take three integers and a String, or another
date instance and a string. IncDate inherits from Date and adds the increment() method that advances the day
by one. In both cases the toString() method prints the date in mo/day/yr format and a method
getDescription() returns the description string.
[10 pts]
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try {
IncDate [] events;
events = new IncDate[10];
events[0] = new IncDate (1,15,2007, “Classes start”);
events[1] = new IncDate (2,2,2007, “Groundhog Day”);
IncDate today = new IncDate(2,7,2007,”CS 240 Exam 1”);
IncDate tomorrow = new IncDate(today,”Work on Program 2”);
tomorrow.___________; //really make it tomorrow
events[2] = today;
events[3] = tomorrow;
events[4] = new IncDate (5,1,2005,”Reading Day”);
} catch (Exception e)
System.out.println(“Error in initialization: “+e.getMessage());
}
for(i=0; i<5; i++){
if(events[i].monthIs()<=2){
System.out.print(events[____].toString() + “-->” +
events [ _____ ] . _____________________()+”\n”);
}
}
a. Fill in lines 17 and 18 to have the date of an event and its description printed. [3]
b. Fill in line 8 to make it correctly “tomorrow” from today. [1]
c. Draw a picture of the memory layout for array events, variables today and tomorrow, and objects
resulting from lines 3-11. [3]
d. What is actually printed by the program segment in lines 15-20 when run? Show, don’t describe. [3]