AP Computer Science Homework Set 3 Class Methods

Transcription

1 AP Computer Science Homework Set 3 Class Methods P3A. Let s upgrade the Song class. Let s make the following upgrades: a. Add a private instance variable yearreleased that stores the year the Song was released. b. Upgrade the Song s constructors to properly initialize the new instance variable yearreleased. c. Add getter and setter methods for the private instance variable yearreleased. These methods will be called getyearreleased() and setyearreleased(). d. Write a method getsonglength() that converts the length of the song in seconds to minutes and second(s). The output of the method should be a String. If the length of the song in seconds is 343, then the method should return the following String: The length of the song is: 5 minutes and 43 seconds. e. Write a new SongDriver class to test the Song s new constructors and setyearreleased() and getyearreleased() and methods. f. Integrate your password program into the setyearrelased() method so that that yearreleased instance variable can only be set if the correct username and password are input. Page 1

2 P3B. Time to upgrade the Clock class. The Clock class should include the following upgrades: a. a public setter method called settime() should be written that takes three integer parameters to set the Clock s hours, minutes, and seconds, respectively, b. a public method setdaylightsaving( int hours ) that increments or decrements the hours of the Clock by the number specified by the parameter hours. The parameter hours will essentially be 1 or -1 depending on whether we are Springing forward or Falling back. Don t worry about noon and midnight conditions; this will be in a future upgrade. c. a public method totalseconds() that returns the total number of integer seconds represented the numbers of hours, minutes and seconds on the Clock (for a future Stopwatch upgrade.) For example, the method should return 3661 if the Clocks reads 1 hour, 1 minute, and 1 second. Note that no separate totalseconds private instance variable should be included in this class. The method totalseconds() can return a value that can be calculated at any time from the existing hours, minutes, and seconds private instance variables. d. upgrade the tostring() method so that it also returns the total seconds in a user-friendly format. Write a driver class to test the settime(), setdaylightsavings( int hours), and totalseconds() methods. The driver should perform the following actions: a. Create an instance of a Clock object, b. Print the Clock using its tostring() method, c. Use the settime() method to set the Clock s time to a non-zero time d. Print the Clock again using its tostring() method, e. Use the setdaylightsaving( int hours ) method to adjust the time of the Clock by the hours parameter, f. Print the Clock again using its tostring() method. Page 2

3 P3C. Let s upgrade the Student class from HW 2 to add the capability to store and process grades. Below are the following specifications: a. Add an instance variable of type array called grades that can hold five double variables for the student s grade point averages for each of his/her five classes (English, Math, Science, Fine Arts, Social Sciences). The following scale will be used: A = 4.00 A- = 3.70 B+ = 3.30 B = 3.00 B- = 2.70, etc. b. Upgrade the zero-argument constructor to initialize all elements of the grades array to 0.0. c. Upgrade the multi-argument constructor so that it also initializes the array of grades with 5 double values in the following order: English Math Science Fine Arts Social Science d. Add a public method setgpa()that will take 5 double parameters to set the GPAs for each of the courses stated above in the order stated above. e. add a public method, calcgpa(), that will calculate and return the average GPA for the student as a double value. f. Upgrade the tostring() method that will return a String that includes the student s name and average GPA. Page 3

4 Write a driver class to: a. Create a Student senior using the multi-argument constructor with following information: First Name = Joe Last Name = Senior English = 4.0 Math = 4.0 Science = 3.5 Fine Arts = 4.0 Social Science = 4.0 b. printout the student s name and average GPA using the tostring() method, c. set the five GPA s using the setgpa() method to all 4.0, and d. printout the student s name and average GPA using the tostring() method a second time after the grade change. Page 4

5 P3D. More upgrades to the Student class! Add method getgrade() to the Student class that will return a String letter grade based on the student s GPA. The method should return (not print) A if the GPA is greater than 4.00, B if the GPA is greater than 3.00, C if the GPA is greater than 2.00, D if the GPA is greater than 1.00, and F otherwise. Write a driver class to create two student objects, sets the GPA of the students using the setgpa() method and prints the letter grade of each student. Sample output is shown below: Page 5

6 P3E. Write a program that creates three String objects. Each String should be the name of a university to which you are applying. Now we are going to compare the universities with the String method compareto(). Print out the result of comparing each school to another. For example, if s1 and s2 are defined as follows: String school1 = new String ( Stanford ); String school2 = new String ( Oregon ); String school3 = new String ( UCLA ); We can compare the schools as follows: System.out.println( school1.compareto( school2 ); Answer the questions below in a comment after all of your source code: a. What is the output of the compareto() method telling us? b. Compare to schools that have the same first letter and a different second letter. What does compareto() do in this case? P3F. AP Packet 2010 #2 APLine (Class Design). Mr. Lew will brief you on this question. P3G. Write a program that searches for a given integer in an array of integers. Specifically, write a program that performs the following tasks: a. create an array of 10 integers in ascending, non-sequential order. And fill the array with the following numbers: b. use a for loop to traverse the array and return the index number of the location of the integer you wish to find. For example, in the array above, if the number to find is 9, the program should return the index number 5 in a userfriendly phrase. c. If the number is NOT found in the array, return -1. Page 6

7 P3H. Write a program that creates an array that can hold 5 String objects. Populate the array with the names of your current teachers. Use a for-each loop to traverse the array and print the names of each of your teachers. P3I. Write a Create new password program that requires passwords to have a length of at least 6 characters and at least one non-alphanumeric character (+, -, *, / Passwords that do not meet these requirements should be rejected. Use the String method substring() which returns String that is part of or substring of a given String. Consider the following example: String password = new String( "abc*d_" ); System.out.println( password.substring( 3,4 ) ); // prints * Since the substring method returns a String, you can compare it to another String using.equals(). Below, we extract one letter from the password and determine if it is equal to *. String oneletter = new String( password.substring( 3,4 ) ); oneletter.equals( * ); // result is true By the end of the lesson students should be able to: a. Write the Java code to correctly initialize each primitive type with appropriate data values. b. Write the Java code that uses the new operator to instantiate objects. c. Write the Java code that uses the dot operator to change the value of an object s data values. d. Write the Java code to create an array of primitive types or objects and assign primitive data values to elements of the array. Page 7