Directions: Fill in answers on the pages below. Don't spend too much time on any one problem.

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1. if-else: Write a segment of code that uses one or more if-else statements to set the tax rate (variable taxRate) based on income (variable income), using on the table below. Then calculate a value for a double variable named tax which is the income times the tax rate. Finally print either You owe and the tax, in case the tax is greater than zero, or print You owe nothing in case the tax is zero.

   income	taxRate
   <= 10000	0
   > 10000 and <= 50000	.20
   > 50000 and <= 200000	.35
   > 200000	.50

   Answers are in red below.

   Income.java

   One run

   import java.util.Scanner; public class Income { public static void main(String[] args) { int income; double taxRate; Scanner in = new Scanner(System.in); income = in.nextInt(); while (income >= 0) { // put if-else statement(s) here to // give taxRate the proper value if (income <= 10000) taxRate = 0.0; else if (income <= 50000) taxRate = 0.2; else if (income <= 200000) taxRate = 0.35; else taxRate = 0.5; System.out.println("income: " + income + ", taxRate: " + taxRate); // statement here to give tax the proper value double tax = income*taxRate; // statements here to print the proper message if (tax > 0.0) System.out.println("You owe " + tax); else System.out.println("You owe nothing"); income = in.nextInt(); } } }

   9999 income: 9999, taxRate: 0.0 You owe nothing 10000 income: 10000, taxRate: 0.0 You owe nothing 10001 income: 10001, taxRate: 0.2 You owe 2000.2 50000 income: 50000, taxRate: 0.2 You owe 10000.0 50001 income: 50001, taxRate: 0.35 You owe 17500.35 100000 income: 100000, taxRate: 0.35 You owe 35000.0 200000 income: 200000, taxRate: 0.35 You owe 70000.0 200001 income: 200001, taxRate: 0.5 You owe 100000.5 0 income: 0, taxRate: 0.0 You owe nothing -1

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2. while loop: Write a while loop (or any other kind of loop, but your answer must use a loop) that will print the even numbers from 1 to 20, with a space after each one, that is, it should print 2 4 6 8 10 12 14 16 18 20.

   int k = 2;
   while (k <= 20) {
      System.out.print(k + " ");
      k = k + 2;
   }
   System.out.println();
   

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3. for loop:
   1. Rewrite the following for loop as a while loop that will print the same thing.

   2. Say exactly what this loop will print.

      for (int i = 1; i < 6; i++) {
         System.out.println(i + " squared = " + i*i);
      }
      
      // for loop as a while below
      int i = 1;
      while (i < 6) {
         System.out.println(i + " squared = " + i*i);
         i++;
      }
      
      // what the loop will print below
      1 squared = 1
      2 squared = 4
      3 squared = 9
      4 squared = 16
      5 squared = 25
      

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4. Sum using a loop: Use a loop to calculate the sum of the numbers from 1 to 100. After the loop, print this sum.

   public class Testit {
   
      public static void main(String[] args) {
         int sum = 0;
         for (int i = 1; i <= 100; i++)
            sum = sum + i;
         System.out.println(sum);
      }
   }
   Output: 5050
   

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5. The Student class and StudentTest class: Here are two classes with parts missing and some questions at the end. Answers are in red below.

   public class Student {
      private String myName; // Student's name
      private int myNumberOfCourseHours; // number of course hours
      private int myTotalGradePoints; // total grade points
   
      // put constructor below (Part a)
      public Student(String name) {
         // new student, with name, but no quizzes
         myName = name;
         myNumberOfCourseHours = 0;
         myTotalGradePoints = 0;
      }
   
      // put accessor method for myName below (Part b)
      public String getName() {
         // return the student's name
         return myName;
      }
   
      public int getNumberOfCourseHours() {
         return myNumberOfCourseHours;
      }
      
      public int getTotalGradePoints() {
         return myTotalGradePoints;
      }
   
      public void addSemester(int courseHoursTaken, int gradePointsEarned) {
         if (courseHoursTaken <= 0)
            System.out.println("Incorrect input data\n");
         else {
            myNumberOfCourseHours = myNumberOfCourseHours + courseHoursTaken;
            myTotalGradePoints = myTotalGradePoints + gradePointsEarned;
         }
      }
      
      // put definition of helper method getGPA below (Part c)
      public double getGPA() {
         if (myNumberOfCourseHours == 0)
            return -1.0;
         else
            return (double)myTotalGradePoints/myNumberOfCourseHours;
      }
   
      public String toString() {
         return "Name: " + getName() +
            "\n   course hours: " + getNumberOfCourseHours() +
            "\n   grade points: " + getTotalGradePoints() +
            "\n   grade point average: " + getGPA();
      }
   }
   //----------------------------------------------------------
   public class StudentTest {
   
      public static void main(String[] args) {
         // put answers to Part d below
         Student frank = new Student("Frank Griswold");
         System.out.println(frank);
         frank.addSemester(6, 15);
         System.out.println(frank);
         System.out.println("Frank's GPA: " + frank.getGPA());
         frank.addSemester(9, 24);
         System.out.println(frank);
      }
   }
   Output:
   Name: Frank Griswold
      course hours: 0
      grade points: 0
      grade point average: -1.0
   Name: Frank Griswold
      course hours: 6
      grade points: 15
      grade point average: 2.5
   Frank's GPA: 2.5
   Name: Frank Griswold
      course hours: 15
      grade points: 39
      grade point average: 2.6
   

   1. Fill in a constructor for Student that sets myName equal to the input formal parameter, and sets the other two private data members to 0.
   2. Fill in a public accessor function getName that returns the name.
   3. Fill in a public helper function getGPA that returns the grade point average (GPA) as a double. The GPA is the total number of grade points divided by the number of course hours. In case the number of course hours is 0, you should return -1.0.
   4. Inside the main function give code to do the following:
      1. Give code to create an instance of Student with variable name frank and with the actual parameter "Frank Griswold".
      2. Use the toString method to print all the information about this instance (which will have a GPA of -1.0).
      3. Use the addSemester method to add in 6 credit hours and 15 total grade points.
      4. Again use the toString method to print all the information about this instance.
      5. Use an explicit call to getGPA to print the GPA for Frank.

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6. The Date class and DateTest class:
   1. Write a Date class below from scratch. Date has the following parts.
      1. private data members (also called instance variables in the course) for the day, the month, and the year, all integers.
      2. A constructor that takes in the day, month, and year in that order as formal parameters. In case the day is not in the range from 1 to 31 (inclusive), the constructor should set the variable for day to 0. Similarly, the constructor should check that the month is between 1 and 12 (inclusive), and should check that the year is between 1900 and 2100 (inclusive).
      3. Accessor methods for the three data members.
      4. A toString method that returns the date as a String in the American notation, that is, in the form: mm/dd/year, where mm is one or two digits for the month, dd is one or two digits for the day, and year is 4 digits for the year.
      5. A nextDay method that increases the day by one.
         • If the month number is 4, 6, 9, or 11, and if the day number is 31, set the day to 1 and increase the month number by 1.
         • If the month number is 2, and if the day number is 29, set the day to 1 and increase the month number by 1.
         • Otherwise, if the day number is 32, set the day to 1 and increase the month number by 1.
         • After the above, if the month number is 13, set the month number to 1 and increase the year number by 1.

   2. Write a DateTest class below from scratch. DateTest should the following.
      1. Create an instance of Date with variable name today, and with actual parameter values of 13, 12, and 2005.
      2. Use toString to print today.
      3. Use nextDay to move to the next day.

   Below, I used an extra method daysInMonth that wasn't asked for, but then it is easy to check for incorrect initial dates with myDay < 31. I also put in a leading zero on months or days less than 10, and this wasn't asked for. This does not handle leap year or Feb. 29.

   Date.java

   DateTest.java, plus run

   // Date: represent dates public class Date { private int myDay; // 1-28, 30, 31 private int myMonth; // 1-12 private int myYear; // 1900-2100 public Date(int day, int month, int year) { // if error, set field to 0 if (day < 1 || day > daysInMonth(month)) day = 0; myDay = day; if (month < 1 || month > 12) month = 0; myMonth = month; if (year < 1900 || year > 2100) year = 0; myYear = year; } private int daysInMonth(int month) { // incorrect on month == 2 in leap year if (month == 2) return 28; if (month == 4 || month == 6 || month == 9 || month == 11) return 30; return 31; } public int getDay() { return myDay; } public int getMonth() { return myMonth; } public int getYear() { return myYear; } public String toString() { String res = ""; // put in leading 0 on day if (myDay < 10) res = res + "0"; res = res + myDay; res = res + "/"; // put in leading 0 on month if (myMonth < 10) res = res + "0"; res = res + myMonth; res = res + "/"; res = res + myYear; return res; } public void nextDay() { if (myDay == daysInMonth(myMonth)) { myDay = 1; myMonth++; } else myDay++; // in case above incremented myMonth if (myMonth == 13) { myMonth = 1; myYear++; } } }

   public class DateTest { public static void main(String[] args) { Date today = new Date(13, 12, 2005); System.out.println(today); today.nextDay(); System.out.println(today); System.out.println(); Date newYearsEve = new Date(31, 12, 2005); System.out.println(newYearsEve); newYearsEve.nextDay(); System.out.println(newYearsEve); System.out.println(); Date endOfFeb = new Date(28, 2, 1998); System.out.println(endOfFeb); endOfFeb.nextDay(); System.out.println(endOfFeb); System.out.println(); Date testDate = new Date(29, 2, 2100); System.out.println(testDate); testDate.nextDay(); System.out.println(testDate); System.out.println(); } } // a run of this program 13/12/2005 14/12/2005 31/12/2005 01/01/2006 28/02/1998 01/03/1998 00/02/2100 01/02/2100

Points for each problem: 1-30, 2-20, 3-25, 4-25, 5-50, 6-50.