Improving java code (using methods involving arrays)

Simple refactored example:

public class UserInteraction {

    public static void main(String[] args) {
        UserChoiceManager userChoiceManager = new UserChoiceManager();
        UserChoice choice = UserChoice.UNKNOWN;

        do {
            choice = userChoiceManager.manage();
        } while (choice != UserChoice.EXIT);

        System.out.println("Bye!");
    }
}

public enum UserChoice {
    UNKNOWN(0),
    ENTER_SUBJECT(1),
    DISPLAY_DATA(2),
    CALCULATE_AVERAGE_GRADE(3),
    EXIT(4);

    private int id;

    public int getId() {
        return id;
    }

    UserChoice(int id) {
        this.id = id;
    }

    public static UserChoice getById(int input) {
        for (UserChoice value : UserChoice.values()) {
            if (value.getId() == input) {
                return value;
            }
        }
        return UserChoice.UNKNOWN;
    }

}

public class Subject {

    private String name;

    private int grade;

    public Subject(String name, int grade) {
        this.name = name;
        this.grade = grade;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getGrade() {
        return grade;
    }

    public void setGrade(int grade) {
        this.grade = grade;
    }

}

public class UserChoiceManager {

    private final static int SUBJECT_COUNT = 10;

    private Subject[] subjects = new Subject[SUBJECT_COUNT];

    private Scanner scan = new Scanner(System.in);

    public UserChoiceManager() {
    }

    public UserChoice manage() {
        System.out.println(printHelp());

        UserChoice choice = getUserChoiceById(scan);

        if (choice == UserChoice.ENTER_SUBJECT) {
            choice = enterSubjects(choice);
        }

        if (choice == UserChoice.DISPLAY_DATA) {
            printSubjectsAndGrades();
        }

        if (choice == UserChoice.CALCULATE_AVERAGE_GRADE) {
            printAverageGrade();
        }

        return choice;
    }

    private static String printHelp() {
        StringBuilder usage = new StringBuilder("\nUsage:\n");
        usage.append(UserChoice.ENTER_SUBJECT.getId()).append(". Enter a course name and a grade").append("\n");
        usage.append(UserChoice.DISPLAY_DATA.getId()).append(". Display all grades").append("\n");
        usage.append(UserChoice.CALCULATE_AVERAGE_GRADE.getId()).append(". Calculate the average grade").append("\n");
        usage.append(UserChoice.EXIT.getId()).append(". Exit program");

        return usage.toString();

    }

    private UserChoice getUserChoiceById(Scanner scan) {
        return UserChoice.getById(scan.nextInt());
    }

    private UserChoice enterSubjects(UserChoice choice) {
        System.out.println("Enter " + subjects.length + " subjects and their corresponding grades:");
        System.out.println();

        for (int i = 0; i < subjects.length; i++) {
            String subjectName = scanSubjectName();
            int grade = scanGrade();
            subjects[i] = new Subject(subjectName.toLowerCase(), grade);
        }

        System.out.println("Thank you!");
        System.out.println();

        return choice;
    }

    private String scanSubjectName() {
        Scanner temp = new Scanner(System.in);
        String subjectName = "";
        do {
            System.out.println("Subject:");
            subjectName = temp.nextLine();
            if (subjectName.equals("")) {
                System.out.println("Empty subject name! Try again.");
            }
        } while (subjectName.equals(""));

        return subjectName;
    }

    private int scanGrade() {
        int grade = 0;
        do {
            Scanner temp = new Scanner(System.in);
            System.out.println("Grade:");
            try {
                grade = temp.nextInt();
            } catch (InputMismatchException e) {
                System.out.println("Invalid grade. Enter numeric value! Try again.");
            }
        } while (grade == 0);

        return grade;
    }

    private void printAverageGrade() {
        System.out.println("Total of grades: " + getSum(subjects));
        System.out.println("Count of grades: " + subjects.length);
        System.out.println("Average of grades: " + getAverage(subjects));
        System.out.println();
    }

    private void printSubjectsAndGrades() {
        System.out.println("Subjects" + "\tGrades");
        System.out.println("---------------------");

        for (int p = 0; p < subjects.length; p++) {
            System.out.println(subjects[p].getName() + "\t" + "\t" + subjects[p].getGrade());
        }
    }

    public static double getAverage(Subject[] subjects) {
        int sum = 0;
        for (Subject s : subjects)
            sum += s.getGrade();
        return ((double) sum) / subjects.length;
    }

    public static double getSum(Subject[] subjects) {
        int sum = 0;
        for (Subject s : subjects) {
            sum += s.getGrade();
        }
        return sum;

    }
}