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

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1 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 indicated point values. There are 2 programs to write. There are 114 points on this test which means you can earn up to 14 extra points towards your test average. Remember that only the Command Box and Notepad++ with no other programs available may be 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. _F_ a. References to String objects cannot be passed to methods. _T_ b. float and int variables use the same number of bytes. _T_ c. ( JAMES.compareTo( James ) < 0) evaluates as true. _T_ d. (!false (!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. ( AB == ( A + B )) is true. _T_ j. A for loop can be nested inside an if-else block. _F_ k. If the pattern String 0.### is applied during output it guarantees that the printed number will always display three decimal places. 1

2 2. Write -47 in two s complement using 8 bits flip add 1 3. The object-oriented language feature that packages attributes and behaviors into a single unit is called encapsulation 4. When a String array is instantiated each cell has the value null. 5. Given the following array: int [][] table ={{1,4,7}, {1,2,3,4,8}, {1,2,0,5}, {4,9,8,6,3,16}}; What is the value of table[2].length? 4 6. In which package is the File class found? java.io 7. If String text = ILoveJava ; then the value of text.substring(4,7) is eja. 8. How many bytes does the following statement reserve for the cells in the array called strarray: String[] strarray = new String[12]; 96 2

3 9. Provide examples of two different ways that methods can be overloaded a. b. public static void mymethod1(int x) public static void mymethod1(string [] sarray) public static double mymethod2(int x) public static double mymethod2(int x, double y) 10. Bytecode is produced by the java compiler and is used as input to the JVM. 11. Given: double x = ; and the format pattern is 00.## the printed output String of x when using the format pattern will be 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 String array. public static String [] stringarray(string str1, char xchar) 13. System.out.println( (9 + 4) + +( B )); prints out as 13B. 3

4 14. What is the printout of the following code fragment? int j=0, k=1; while(j<8) { System.out.print(k + ); k=k + (j%3); j=j+1; } What is the printout from the following code segment: String growth = ABC ; char letter = d ; for (int i=0; i <4; i++) { growth = growth + letter; letter = (char)(letter-1); System.out.println(growth); } ABCd ABCdc ABCdcb ABCdcba 4

5 16. Assume static Random randy = new Random(); Write a statement that randomly selects an integer from 0,1,2,3,4,5,6,7,8,9 and assigns it to the variable int number. int number = randy.nextint(10); 17. How many String objects are created by executing the following code fragment? String str1 = new String ( Sunny ); String str2 = Sunny ; str3 = str2; String str4 = str1+str2; 2 5

6 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. PercentTrue (32 points) Write a program with four methods. The main method does the following: (10) a. Requests from the user the dimensions of a two dimensional array. b. Calls createarray which creates a two-dimensional boolean array with the dimensions read in. c. Calls a method booleanfull that randomly fills the two-dimensional array with either true or false. d. Calls a second method called calcpercent that returns the percentage of cells that are true. e. Prints out the boolean array row by row. f. Then prints out the following sentence with the percentage correct rounded to two decimal places: The percent of elements that are true in the array is percenttrue%. The method createarray does the following: (5) a. Accepts the dimensions of the array as formal parameters. b. Creates a boolean two-dimensional array with those dimensions. c. Returns a reference to the two-dimensional boolean array. The method booleanfull does the following: (8) a. Accepts a reference to a two dimensional boolean array. b. Fills each cell with a randomly generated true or false value starting from a seed equal to 2. The method calcpercent does the following: (9) a. Accepts a reference to a two-dimensional boolean array. b. Calculates the percentage of the elements with the value true as type double. c. Returns the percentage as a type double. 6

7 4 5 true false true false false true true false true true true false false true false true true false true true The percent of elements that are true is 60%. 1 3 true false true The percent of elements that are true is 66.67%. 7

8 2. NameSubstrings (26 Points) The method main does the following: (16) a. Requests the name of an input file and uses it to create a Scanner for that input file. b. Requests the name of an output file and uses it to create a PrintWriter. c. Creates a one-dimensional String array with 100 rows. d. Reads in first names from the input file into the String Array. You may assume that the file has no more than 100 names. Also assume that each name has at least 3 characters. There could be more than one name on a line. e. Calls nofirst with a reference to the String array created, and the number of names read in, to create a set of Strings and return a reference to a different one-dimensional String array as described below. f. Prints to the output file on a separate line the String in each row of the original array followed by a space followed by the String created in nofirst. nofirst: (10) a. Accepts the reference to a one-dimensional array and the number of names that were read in from the input file in main. b. Creates a new one-dimensional String array with the length equal the number of the number of names read in (the second parameter in the header). c. Obtains a substring that includes all but the first character of the String and place the new substring created into a corresponding row in the new one-dimensional String array. d. Returns a reference to the new one-dimensional String array. Example: If input file is: James Henry Vasquez Bustos Smith Sanchez Smith Delorenza Mendoza Leon Henry The output file, line by line, would be: James ames Henry enry Vasquez asquez Bustos ustos Smith mith Sanchez anchez Smith mith Delorenza elorenza Mendoza endoza 8

9 Leon eon Henry enry 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.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 same as above ignoring case compares two strings s.comparetoignorecase(t) same as above ignoring case 13