Exam 1 Answer Key CSC 123 Fall 2018 Lecturer: Howard Rosenthal Oct. 17, 2018

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1 Your Name: Exam 1 Answer Key CSC 123 Fall 2018 Lecturer: Howard Rosenthal Oct. 17, 2018 The following questions in numbers 1-11 are all worth 3 points each (including each true and false). The programs have indicated point values. There are 2 programs to write. There are 120 points on this test which means you can earn up to 20 extra points towards your test average. Remember that only the text processor (Geany) terminal and Eclipse with no other programs may be used with no other programs open until you are ready to the programs. You are allowed to bring 2 double sided or 4 single sided sheets into the test with you. On the last two sheets you will find the ASCII character to decimal conversion, and some common String methods. You can detach these sheets for easier use. 1. Answer the following as true or false. _T a. A reference to a Scanner object can be passed to a method. _T b. short and char variables use the same number of bytes. _F c. ( John.compareTo( JOHN ) < 0) evaluates as true. _T d. (!true (true &&!false)) always evaluates as true. _F e. Classes are instantiations of objects. _F f. Array indices can be expressed as floating point numbers since they will cast down. _F g. Every row of a two dimensional array must be of the same length. _T h. Unicode characters always require two bytes in Java. _F i. ( ABC == ( A + B + C )) is true. _T j. A for loop can be nested inside an if block. 2. The object-oriented language feature that packages attributes and behaviors into a single unit is called encapsulation 1

2 3. When a String array is instantiated each cell has the value null. 4. Given the following array: int [][] table ={{1,4,7,8}, {1,2,3,4,8}, {1,2,0,5}, {4,9,8,6,3,16}}; What is the value of table.length? 4 5. If String text = I was a Jedi Warrior ; then the value of text.substring(8,12) is _ Jedi. 6. How many bytes does the following statement reserve for the cells in the array called scanarray: Scanner [] scanarray = new Scanner[6]; Provide examples of two different ways that methods can be overloaded a. public static void meth1(int a, int b) public static void meth1(int a, double b) b. public static void meth1(int a, int b) public static void meth1(int a, int b, int c) 8. Write a method header for a method called stringarray with two formal parameters String str1 and char xchar that returns a reference to a one-dimensional char array. public static char [] stringarray(string str1, char xchar) 9. How many String objects are created by executing the following code fragment? String str1 = new String ( Sunny ); String str2 = Cloudy ; String str3 = Sunny ; String str4 = str2; String str5 = str1+str2; 3 2

3 10. What is the printout of the following code fragment? int j=0, k=1; while(j<17) { System.out.printf( %d,k); k=k + (j%5); j=j+3; } What is the printout from the following code segment: String growth = CBA ; char letter = d ; for (int i=0; i <4; i++) { growth = growth + letter; letter = (char)(letter-1); System.out.printf( %s, growth); } CBAdCBAdcCBAdcbCBAdcba 3

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5 Programs: It is important to follow the instructions in each problem. two.java files to Do not mail these files until you are done with the entire exam. No second mailing will be allowed. 1. ColumnSums (30 points) Write a program with four methods. The main method does the following: (6) a. Create an input Scanner to read from the keyboard entries. b. Requests the number of rows and columns of a two-dimensional array. The minimum number of rows is 3 and the minimum number of columns is 4. You must reject lower numbers and request a correct value. c. Calls createintegerarray passing to it the number of rows and columns, and accepting a reference to a two-dimensional array. d. Calls fillarray with the reference to the two-dimensional array. fillarray performs the actions described below. e. Call columnadder and accept the double value returned as described below. f. Call printresults with a reference to the two-dimensional int array and a double value with the percentage returned from columnsum. The method createintegerarray does the following: (4) a. Accepts the dimensions of the array as formal parameters. b. Creates an int two-dimensional array with those dimensions. c. Returns a reference to the two-dimensional int array. The method fillarray does the following: (6) a. Accepts a reference to the two dimensional int array. b. Creates a Random object. c. Fills each cell for all but the last column in each row with a randomly generated integer value between 1 and 12. The method columnadder does the following: (8) a. Accepts a reference to the two-dimensional int array. b. Places the sum of all the previously entered values of the cells in each row in the final column for the row. c. Returns the percentage of values in the last column that are greater than 6.5*(number of columns -1) as a double. The method printresults does the following: (6) a. Accepts a reference to the two-dimensional int array and a double value with the percentage. b. Prints out the two dimensional array row by row with each column right justified. This includes the last column of each row that contains the sum of the columns for that row. c. Prints out a sentence that reads as follows with the italics replaced by values. Percent should be printed to two decimal places, The percentage of elements in the last column greater than 6.5*(numcols-1) is percentage. 5

6 A couple of examples of input and output: Please enter the number of rows in the two-dimensional integer array Must have at least 3 rows: 5 Please enter the number of columns in the two-dimensional integer array Must have at least 4 columns: The percentage of elements greater than is 0.00 Please enter the number of rows in the two-dimensional integer array Must have at least 3 rows: 5 Please enter the number of columns in the two-dimensional integer array Must have at least 4 columns: The percentage of elements greater than is

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8 2. ReadWriteStrings (30 Points) This program will read in lines one at a time from a file and write output to a file as described below. You will need to create a physical file to read in from with several lines of text. The method main does the following: (8) a. Creates a Scanner to read from the keyboard. b. Reads in the name of the physical file to be read from (Hint: use next, not nextline). c. Calls createfilescanner with the name of the physical file to read from, receiving the reference to the Scanner as the return value in a Scanner variable. d. Reads in the name of the physical file to write to. e. Calls createprintwriter with the name of the physical file to write to, receiving the reference to the PrintWriter as the return value in a PrintWriter variable. f. Create a one-dimensional String array of length 100. g. Call readinlines with a reference to the Scanner created to read from the file, and a reference to the String array, returning an int with the number of lines read in. h. Call writevowels with a reference to the PrintWriter, to the String array described above and to an int with the number of lines read into the array as described above, and then perform the functions described below, accepting the number of vowels written to the output file as a return value. i. Write the number of vowels written to the screen in a sentence stating the total number of vowels. j. Close the Scanner and PrintWriter objects. createfilescanner: (4) a. Accepts as a String the name of the physical file. b. Creates a Scanner throwing an exception if the physical file doesn t exist. c. Returns a reference to the Scanner. createprintwriter: (4) a. Accepts as a String the name of the physical file. b. Creates a PrintWriter. c. Returns a reference to the PrintWriter. readinlines: (6) a. Accepts a reference to the Scanner for the physical file, and to a String Array. b. Read in the up to the first 100 lines in the file and place a reference to each line in the String array. c. Return an int with the number of lines read in. writevowels: (8) a. Accepts three parameters including a reference to the PrintWriter, to the String array described above and to an int with the number of lines read into the array. 8

9 b. Capitalize and then write the vowels in each line in the String array to a line in the output file using PrintWriter followed by a space, followed by the number of vowels written on that line. (Vowels are A, E, I, O and U). Vowels in original String can be upper case or lower case. (All output should be all upper case). To do this extract each character in the line and see if it matches a vowel using either if statement(s) or a switch block. Return the total number of vowels written to the file. (Hint: Easiest to create a complete String of the vowels for each line before writing. However, you could also write each vowel character individually and keep track for each line. c. Return an int with the total number of vowels written. A Sample of Input and Output Please enter the name of the input file:testfilereadlines.txt Please enter the name of the output file:outputs.txt The total number of vowels read is 40 The input file in this case is : My interesting experience. Enter a bunch of numbers Henry ate dinner? Who #### is that!!! My friend is fine. Your friend is not fine Goodbye The output file is: IEEIEEIEE 9 EEAUOUE 7 EAEIE 5 OIA 3 IEIIE 5 OUIEIOIE 8 OOE 3 9

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13 Common String Methods str.charat(k) str.substring(k) s.substring(k, n) str.indexof(s) str.indexof(s, k) str.startswith(s) str.startswith(s, k) str.equals(s) str.touppercase() str.equalsignorecase(s) str.compareto(s) returns a char at position k in str. returns a substring from index k to the end of str returns a substring from index k to index n-1 of str returns an index of the first occurrence of String s in str; an unsuccessful search returns -1. returns an index of String s starting an index k in str; an unsuccessful search returns -1. returns true if str starts with s returns true if str starts with s at index k returns true if the two strings have equal values Returns a new String in which all characters are still there, but all alpha characters are now upper case same as above ignoring case compares two strings s.comparetoignorecase(t) same as above ignoring case 13

Final Exam. CSC 121 Spring Lecturer: Howard Rosenthal. May 17, 2017

Final Exam. CSC 121 Spring Lecturer: Howard Rosenthal. May 17, 2017 Final Exam. CSC 121 Spring 2017 Lecturer: Howard Rosenthal May 17, 2017 Your Name: Answer Key The following questions (or parts of questions) in numbers 1-17 are all worth 2 points each. The programs have