CSC120 Final Exam
1. (3 points) Writing a program that receives a ile path from the user and writes to a ile of the given path requires importing four classes. You can accomplish this with
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import java . io .*; import java . util . Scanner ; |
but without using the *, you need to state the three classes from java.io, as in:
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import java . io . XXX ; // for a file import java . io . YYY ; // for printing import java . io . ZZZ ; // for run -time error |
State the three classes indicated as XXX, YYY, and ZZZ.
2. (4 points) State the output of the following code fragment.
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int c = 0 , d ; for ( int i = 1000; i > 1; i = i / 4 + 1 ) { c ++; d = ( int )( Math . sqrt ( c ) ); System . out . printf ( "%04 d :%03 d :%+03 d \ n " , i , c , d ); } |
3. (11 points) Write a public static method unique that receives a String[] parameter named words and returns an int representing how many diferent values appear in the array. For example, if words is array with elements {"abc", "def", "abc", "def", "def"} returns 2. A suggested solution is as follows:
(i) Create the exact copy of words.
(ii) Sort the elements in the copy from (i).
(iii) Find out for how many values of i the sorted array has identical values between positions i-1 and i.
(iv) Return the length of the array minus the quantity from (iii).
You may assume that import java.util.*; appears at the start of the class ile in which this method appears.
4. (25 points) Write a program named Hashes for the following task:
. Receive a path to an input ile and a path to an output ile.
. If the iles are identical (in terms of the full paths), print an error message "Identical files!".
. Otherwise, if the ile speciied by the input path does not exist, is not a regular ile, or is not readable, produce an error message "An invalid file!".
. Otherwise, read the contents of the ile line by line, and print the contents into the output ile with a preix attached to each line, where the preix rotates among #, ##, and ### in this order, starting with #.
Suppose we have a text ile named nightingale.txt, whose contents are:
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" When two lovers meet in Mayfair ," so the legend tells , " songbirds sing , winter turns to spring . Every winding street in Mayfair falls beneath the spell . " I know such enchantment to be ’ cause it happened one evening to me : |
then the program may go as follows:
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Enter input file path : nightingale . txt Enter output file path : foo . txt |
After successful execution, the contents of foo.txt as:
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#" When two lovers meet in Mayfair ," ## so the legend tells , ###" songbirds sing , # winter turns to spring . ## Every winding street in Mayfair ### falls beneath the spell . " # I know such enchantment to be ## ’ cause it happened one evening to me : |
Also, if the path foobar does not pass the tests, the program may go like:
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Enter input file path : foobar Enter output file path : foobar0 An invalid file ! |
If the user provides the same ile path for both, the program should behave as follows:
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Enter input file path : foobar Enter output file path : foobar Identical files ! |
The program detects the use of identical iles when paths difer but the iles are identical. For example, if ddd is a ile folder, the program may behave as follows:
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Enter input file path : ddd /../ foobar Enter output file path : foobar Identical files ! |
We envision that the source code for this program takes the following form:
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import java . util .*; import java . io .*; public class Hashes { public static void main ( String [] args ) throws ZZZ { Scanner keyboard = new Scanner ( System . in ); System . out . print ( " Enter input file path : " ); String inputPath = . . . // file path [1] System . out . print ( " Enter output file path : " ); String outputPath = // file path [ 1] XXX fIn = // input file [ 1] XXX fOut = // output file [ 1] if ( ) { // check name equality using full paths [ 3] System . out . println ( " Identical paths !" ); } else if ( ) { // check the property [6] System . out . println ( " An invalid file !" ); } else { YYY ppp = // instantiation [ 1] Scanner sss = . . . // [1] int counter = . . . // [1]; while ( . . . ) { // [1] . . . // read , print , and update counter [8] } sss . close (); ppp . flush (); ppp . close (); } } } |
Here each ... represents some missing code fragment and after // appears some hint. Also, XXX, YYY, and ZZZ are from Problem 1. The numbers in the square brackets show the points assigned.