Question

Write a Java program that implements a class called ScoreCalculator. The ScoreCalculator is used to calculate the overall score of a student based on the scores obtained in different subjects. The class should have the following methods:

• addScore(subject: String, score: double): This method adds the score obtained by the student in a particular subject. The subject parameter represents the name of the subject, and the score parameter represents the score obtained. The method should throw an IllegalArgumentException if the subject already exists.

• removeScore(subject: String): This method removes the score obtained in a particular subject. The subject parameter represents the name of the subject. The method should throw an IllegalArgumentException if the subject does not exist.

• calculateOverallScore(): double: This method calculates and returns the overall score of the student by summing up the scores obtained in all the subjects. The method should throw an IllegalStateException if no scores have been added.

Implement the ScoreCalculator class according to the above specifications and demonstrate its usage by creating an instance, adding/removing scores, and calculating the overall score.

Answer

public class ScoreCalculator {
    private Map<String, Double> scores;

    public ScoreCalculator() {
        scores = new HashMap<>();
    }

    public void addScore(String subject, double score) {
        if (scores.containsKey(subject)) {
            throw new IllegalArgumentException("Subject already exists");
        }
        scores.put(subject, score);
    }

    public void removeScore(String subject) {
        if (!scores.containsKey(subject)) {
            throw new IllegalArgumentException("Subject does not exist");
        }
        scores.remove(subject);
    }

    public double calculateOverallScore() {
        if (scores.isEmpty()) {
            throw new IllegalStateException("No scores have been added");
        }
        double overallScore = 0;
        for (double score : scores.values()) {
            overallScore += score;
        }
        return overallScore;
    }
}

Explanation:

• The ScoreCalculator class has a private instance variable scores which is a Map to store the scores obtained in different subjects.

• In the constructor, we initialize the scores map as an empty HashMap.

• The addScore method checks if the subject already exists in the scores map using the containsKey method. If it does, we throw an IllegalArgumentException with an appropriate message. If not, we add the subject and score to the scores map using the put method.

• The removeScore method checks if the subject exists in the scores map using the containsKey method. If it does not, we throw an IllegalArgumentException with an appropriate message. If it exists, we remove the subject from the scores map using the remove method.

• The calculateOverallScore method checks if the scores map is empty using the isEmpty method. If it is, we throw an IllegalStateException with an appropriate message. If not, we iterate over the scores using a for loop and calculate the overall score by summing up all the scores. Finally, we return the overall score.

Example usage:

ScoreCalculator scoreCalculator = new ScoreCalculator();
scoreCalculator.addScore("Math", 90.5);
scoreCalculator.addScore("Science", 85.0);
scoreCalculator.addScore("English", 92.3);

System.out.println("Overall Score: " + scoreCalculator.calculateOverallScore());

scoreCalculator.removeScore("Science");

System.out.println("Overall Score after removing Science: " + scoreCalculator.calculateOverallScore());

Output:

Overall Score: 267.8
Overall Score after removing Science: 182.8

In the example usage, we create an instance of ScoreCalculator and add scores for three subjects. We then calculate the overall score and print it. Next, we remove the score for the "Science" subject and calculate the overall score again to observe the change.