Final Exam. CSC 121 Spring 2016 TTH. Lecturer: Howard Rosenthal. May 17, 2016

Transcription

1 Your Name: Final Exam. CSC 121 Spring 2016 TTH Lecturer: Howard Rosenthal May 17, 2016 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. a. Objects created from the String class are immutable. b. double and long variables use the same number of bits. c. ( JOHN.equals( John ) ) evaluates as true. d. (false&&(true false)) always evaluates as false. e. A reference variable for an object is always initialized to null when it is created. f. Array indices can be expressed as boolean values since arrays sometimes store boolean values. g. The elements of different columns of a two-dimensional array can be of different types if the columns are of different lengths. h. The java.io package contains multiple classes i. ((65 + B ) == ( A + B )) evaluates as true. j. Every method must return a value. k. If the pattern String is applied during output it guarantees that the printed number will always display three decimal places. 1

2 2. Write -26 in two s complement using 8 bits. 3. The object-oriented language feature that packages attributes and behaviors into a single unit is called 4. When a String array is instantiated each cell has the value. 5. Given the following array: table ={{1,4,7,9,11}, {1,2}, {1,2,0}, {4,9,8,6,3,16}} What is the value of table.length? 6. In which package is the Math class found? 7. If String text = MyNameIsAnakin then the value of text.substring(1,4) is. 8. How many bytes does the following statement reserve for the array called barray: boolean[][] barray = new boolean[5][4]; 2

3 9. Provide examples of two different ways that methods can be overloaded a. b. 10. Write the output from this code segment: String orig = ABCDE ; String new = new String(); for (int i=0; i <orig.length(); i=i+2) { new = new+orig.charat(i); } System.out.println(new); 11. Given: double x = ; and the format pattern is 0.# the printed output String will be 3

4 12. What is the output of the following code fragment? for ( int i = 6; i < 10; i++ ) { for (int j=3; j<=5; j++) { System.out.print( i%j + " " ); } } 13. Write a method header for a method called cointoss with two formal parameters int number and String str that returns a boolean value. 14. System.out.println ((3 + 4) ); prints out as. 15. What is the printout from the following code segment: char cx = A ; String str1 = Hello ; System.out.println( str1 + cx + (3 + A )); 4

5 16. Assume: 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. 17. How many objects are created by executing the following code fragment? String str1 = Dog ; String str2 = new String ( Dog ); String str3 = Dog ; String str4 = str3; 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. StringMatch (20 points) Write a program with two methods. main: (10) The main method does the following four times: The main method asks the user to enter a line, reading it in as a String. It then prompts the user for a second String The two Strings are passed to a method called containsstring which returns a value as described below. The main method then prints out a statement that as follows (italics indicate real values should be substituted): It is true/false that str2 is a substring within str1. containsstring: (10) The method containsstring does the following: Returns true if the second String is a substring within the first String, otherwise returns false. (hint: use str1.indexof(str2) look at documentation attached) 6

7 2. NameFile (38 Points) Write a program that does the following. main: (12) Calls createarray to create a two-dimensional String array with 100 rows and 2 columns Reads in the first and last names from a file called inputnames.txt into the two-dimensional array created by createarray. The file should have no more than 100 names. (Hint: Use the method next(), not nextline() to read in the first and last name.) Calls lettercount with a reference to the array created in createarray, and the number of names read in, to count the letters in the first and last name of each name. Calls averagelength with a reference to the array created in lettercount Prints to the file outputnames.txt the last name, first name and letter count for each name in that order. Prints to the screen the average number of characters in the first and last names correct to two decimal places, using an object created from the DecimalFormat class as follows (italics indicate real values should be substituted): The average number of characters in the first and last names of each entry is averagelength. createarray: (8) Creates a two-dimensional String array with 100 rows and 2 columns and returns the reference to that array. lettercount: (10) Accepts the reference to the array originally created in createarray, and the number of names in the array Determines the number of characters in the first and last name in each row of the array. Returns a one-dimensional int array with the count of the characters for a name (total of first plus last name characters) in a row placed into the corresponding row of the int array. This array should have a length that equals the number of lines (first and last names) read in from inputnames.txt. averagelength: (8) Accepts a reference to the one-dimensional array with the lengths. Calculates the average length as a double and returns it as a double. 7

8 Example: If inputnames.txt is: John Smith Rosendo Diaz Maria Francesco The output to the file outputnames.txt would be would be: Smith John 9 Diaz Rosendo 11 Francesco Maria 14 The line written to the screen would be: The average number of characters in the first and last names of each entry is

9 9

10 10

11 11

12 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 12