Java method repeats output incorrectly and too often

Question

I was just trying to get suggestions per the course mentor's advice on StackOverflow. I am sorry.

Answer 1

/**
 * prints a student’s average grade by student ID
 * @param  (String studentID)/     */    
public static void print_average_grade(String studentID)
{
    // Here, you have studentID passed into the function but you are not using it
    for (Student s : studentList)
    {
        // Use the studentID here!
        if(s.getStudentID().equals(studentID)) {
            double total = s.getGrade1() + s.getGrade2() + s.getGrade3();
            double average = total / 3;
            System.out.println("StudentID# " + studentID + "  " + average);
        }
    }
}

Use the studentID passed in as an argument, so that you will print out the average grade for the correct student each time.

Answer 2

You're using two loops, first you use

for (Student s : studentList) {
    print_average_grade(s.getStudentID());
}

to call print_average_grade, passing it the studentID, which you promptly ignore and then loop over all the students, again...

public static void print_average_grade(String studentID) {
    for (Student s : studentList) {

        double total = s.getGrade1() + s.getGrade2() + s.getGrade3();
        double average = total / 3;
        System.out.println("StudentID# " + studentID + "  " + average);
    }

}

Instead, change your print_average_grade method to accept a Student and simply calculate the average for said student

public static void print_average_grade(Student s) {
    double total = s.getGrade1() + s.getGrade2() + s.getGrade3();
    double average = total / 3;
    System.out.println("StudentID# " + studentID + "  " + average);
}

Then in your main, loop, just pass it the Student you want...

for (Student s : studentList) {
    print_average_grade(s);
}

If you "really" need to do this by id, then I would write a method which took a int value (id) and does the lookup passing back the Student object, since you seem to want to do this a few times...(mind you a Map would be more useful)

public Student getStudentById(int id) {
    Student match = null;
    for (Student s : studentList) {
        if (s.getStudentID() == id) {
            match = s;
            break;
        }
    }
    return match;
}