Grade papers

The problem

Write a program that allows a user to enter in test scores. The program should display the average of the test scores and the letter grade that is assigned for the test score average. Use the following grading system:

91 - 100 A
81 - 90 B
71 - 80 C
61 - 70 D
Below 60 F

Breaking it down

Create a grade rangemap

static RangeMap<Integer, String> gradeScale = TreeRangeMap.create();
static {
    gradeScale.put(Range.closed(0, 60), "F");
    gradeScale.put(Range.closed(61, 70), "D");
    gradeScale.put(Range.closed(71, 80), "C");
    gradeScale.put(Range.closed(81, 90), "B");
    gradeScale.put(Range.closed(91, 100), "A");
}

Create test score & letter grade methods

/**
 * Method should calculate the average scores
 *
 * @param grades
 * @return
 */
static double getTestScoreAverages (List<? extends Number> grades) {
    return DoubleMath.mean(grades);
}

/**
 * Method should return the letter grade based on scale
 *
 * @param averageOfAllTestScores
 * @return letter grade
 */
static String getLetterGrade (double averageOfAllTestScores) {
    return gradeScale.get((int) averageOfAllTestScores);
}

Create list to hold test scores

List<Double> grades = Lists.newArrayList();

Create a Scanner object for keyboard input

Scanner keyboard = new Scanner(System.in);

Get users selection

System.out.print("Enter test score (-1 to exit): ");
double selection = keyboard.nextDouble();

while (selection != -1) {
    System.out.print("Enter test score (-1 to exit): ");
    selection = keyboard.nextDouble();
    if (selection != -1) {
        grades.add(new Double (selection));
    }
}

Calculate score, grade and display results

double averageOfAllTestScores = getTestScoreAverages (grades);

String letterGrade = getLetterGrade (averageOfAllTestScores);

System.out.println("Average of test scores: " + averageOfAllTestScores);
System.out.println("Your overall average grade is: " + letterGrade);

Output

Enter test score (-1 to exit): 76
Enter test score (-1 to exit): 49
Enter test score (-1 to exit): 29
Enter test score (-1 to exit): 49
Enter test score (-1 to exit): 0
Enter test score (-1 to exit): 30
Enter test score (-1 to exit): 59
Enter test score (-1 to exit): 68
Enter test score (-1 to exit): -1
Average of test scores: 40.57142857142857
Your overall average grade is: F

Unit tests

@Test
public void test_score_averages () {

    List<Integer> testScores = Lists.newArrayList(50, 50, 75, 75);

    double average = GradePapers.getTestScoreAverages(testScores);

    assertEquals(62.5, average, 0);
}

@Test
public void letter_grade_a() {

    String letterGrade = GradePapers.getLetterGrade(92);

    assertEquals("A", letterGrade);
}

@Test
public void letter_grade_b() {

    String letterGrade = GradePapers.getLetterGrade(82);

    assertEquals("B", letterGrade);
}

@Test
public void letter_grade_c() {

    String letterGrade = GradePapers.getLetterGrade(72);

    assertEquals("C", letterGrade);
}

@Test
public void letter_grade_d() {

    String letterGrade = GradePapers.getLetterGrade(62);

    assertEquals("D", letterGrade);
}

@Test
public void letter_grade_f() {

    String letterGrade = GradePapers.getLetterGrade(52);

    assertEquals("F", letterGrade);
}

Level Up

Display a letter grade for each score
Enhance rounding logic in the letter grade method
Add validation to users input (ie. enter a letter)