Student Manager Project - Part 2: Grade Calculation

Let's Think This Through

In this part, we'll extend the Student class from Part 1 with a core feature. We'll use the HashMap to store subject-score pairs, then loop through values() to calculate the average. We'll write a method that uses an if-else chain to determine the grade letter (A, B, C, F) based on the average score. This is also good practice for the pattern of a method returning a value.

Let's Build It

Add an addScore(String subject, int score) method to the Student class using subjectScores.put(). Write a calculateAverage() method that loops through subjectScores.values(), sums the total, divides by the size, and returns the average as a double (return 0 if the map is empty). In getGrade(), check the result of calculateAverage() with if-else conditions (>=90 for A, >=75 for B, >=50 for C, otherwise F) and return the grade as a String. In the main method, add 3 subject scores for a student and print out their average and grade.

Can add subject-score data into the HashMap using addScore()
Can loop through values() in calculateAverage() and return the average as a double
Can correctly determine the grade letter using an if-else chain in getGrade()

Sample Code

java

class Student {
    private String name;
    private int id;
    private HashMap<String, Integer> subjectScores;

    public Student(String name, int id) {
        this.name = name;
        this.id = id;
        this.subjectScores = new HashMap<>();
    }

    public void addScore(String subject, int score) {
        subjectScores.put(subject, score);
    }

    public double calculateAverage() {
        int total = 0;
        for (int score : subjectScores.values()) {
            total += score;
        }
        return subjectScores.isEmpty() ? 0 : (double) total / subjectScores.size();
    }

    public String getGrade() {
        double avg = calculateAverage();
        if (avg >= 90) {
            return "A";
        } else if (avg >= 75) {
            return "B";
        } else if (avg >= 50) {
            return "C";
        } else {
            return "F";
        }
    }

    public String getName() {
        return name;
    }
}

public class StudentManager {
    public static void main(String[] args) {
        Student s1 = new Student("Aung Aung", 101);
        s1.addScore("Math", 95);
        s1.addScore("English", 82);
        s1.addScore("Science", 88);

        System.out.println(s1.getName() + " - Average: " + s1.calculateAverage()
                + " - Grade: " + s1.getGrade());
    }
}

You should see

The console will print the result in a format like Aung Aung - Average: 88.33... - Grade: B.

5-Minute Try-It

Try changing the grade boundaries (e.g. >=80 for A), give two students different scores, and see how the grades differ — all within 5 minutes.

A Quick Word of Caution

HashMap's values() order isn't guaranteed to match insertion order. It doesn't matter for the average calculation, but do double-check your iteration logic.