Is it possible to call methods by name?

Question

I am building a small quiz application, and I am storing each answer to each question in a database table (using JPA).

I wonder if there is a way to fetch the getters dynamically through a for loop for example (as is possible with javascript), rather than to have to write out each get method.

The code I have (where "answer" is a class with 9 different integers for each answer).

public void parseUserScore(UserAnswers answer) {
    Integer[] answers = new Integer[] {
            answer.getQ1(),
            answer.getQ2(),
            answer.getQ3(),
            answer.getQ4(),
            answer.getQ5(),
            answer.getQ6(),
            answer.getQ7(),
            answer.getQ8(),
            answer.getQ9()
    };
    double totalscore = 0;
    Integer answeredQuestions = 0;
    for (int i = 0; i < answers.length; i++) {
        if (answers[i] > 0) {
            answeredQuestions++;
        }
        totalscore += answers[i];
    }
}

My question is if it is possible to fetch these answers through a foor loop like so:

public void parseUserScore(UserAnswers answer) {
    ArrayList<Integer> list = new ArrayList<Integer>();
    for (int i = 1; i < 10; i++) {
        String methodname = "getQ" + i.toString();
        list.add(i, answer.methodname)
    }   
}

This would be preferable since I would like to use the index of each question to separate them based on their respective categories.

Answer 1

From what you provided in your question I think you should use three entities: User , Question and Answer . A user can ask multiple question and submit multiple answers to questions. An answer belongs always to one question. JPA has some annotations to model these rules:

@Entity
class User {

    @OneToMany(mappedBy = "user")
    Set<Question> questions;

    @OneToMany(mappedBy = "user")
    Set<Answer> answers;

    // Getters & setters

}

@Entity
class Question {

    @ManyToOne
    @JoinColumn(name = "user_id")
    User user;

    @OneToMany(mappedBy = "question")
    Set<Answer> answers;

    // Getters & setters

}

@Entity
class Answer {

    @ManyToOne
    @JoinColumn(name = "user_id")
    User user;

    @ManyToOne
    @JoinColumn(name = "question_id")
    Question question;

    int score;

    // Getters & setters

}

Afterwards you can simply iterate over the answers of a particular user and calculate the total score:

final int totalScore = user.getAnswers().stream().mapToInt(Answer::getScore).sum();

Please note that this is only a basic example. You should also make considerations about cascading updates and fetch types of the relations.

Regarding you question about the for loop: Java provides a feature called 'Reflection'. It is a mechanism for meta-programming and could be used to achieve what you described. However, this is a bad idea because it has some drawbacks and it makes no sense in your case as a user should be able to answer more than 10 questions. In fact you can not know how many answers a user will submit.