How to access Java array list data from another class

Question

I\'m trying to make a quiz in Java but I\'m having trouble accessing the array list data from the tester class and therefore my question text isn\'t showing up. I have three cla

Answer 1

After some alterations, I was able to get your code running. But I have to warn you, there are quite some changes:

• QuizTester now only has a main method to start the program. It will initialize and fill the list with questions and then pass it to the QuizSetUp instance
• I didn't have your Question class, so I reduced it to an ArrayList<String> (just to make sure, that the questions could be passed)
• And I didn't hvae your QuizInterface class so I helped myself with a small implementation that would simply print out the question when a new question gets set

QuizInterface (small helper class)

public class QuizInterface {

    private String text;

    public QuizInterface() {
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
        System.out.println("question text = "+this.text);  // this is just to make sure it worked
    }
}

QuizSetUp (heavily reduced)

public class QuizSetUp {

    private QuizInterface qi;
    private ArrayList<String> questions; // uncommented, it's needed now
    private int counter = 1;
    Random random;
    int randIndex;

    // I chose to pass the list with the constructor but the setQuestions() will do as well
    public QuizSetUp(ArrayList<String> questions) {
        this.questions = questions;
        setInterface();
    }

    // NEW method – but it's not needed
    public ArrayList<String> getQuestions() {
        return questions;
    }

    // NEW method – but it's not needed
    public void setQuestions(ArrayList<String> questions) {
        this.questions = questions;
    }

    private enum QuAnswer {
        CORRECT, INCORRECT
    }

    public void setInterface() {
        qi = new QuizInterface();
//        test = new QuizTester();   // this is no longer needed since QuizTester is only used to start the program
    }

    public void pickQuestion() {
        randQuestion();
        setQuestion();   // randIndex is already a global variable in this class, no need to pass with the method call
    }

    public void setQuestion() {
        // QuizInterface has a new method now called "setText()"
        // so here we access the list "questions" (it is already initialized, because we pass it to this class when constructing it)
        // this.randIndex is global, so we can use it directly in this method as an index to the questions list (as you already did it)
        qi.setText(this.questions.get(this.randIndex));
    }

    public void setNextQuestion() {
        //qi.getTimer().cancel();
        //qi.cancelInterval();
        if (counter < 5) { //users must answer five questions to complete quiz
            pickQuestion();
        } else {
            //JOptionPane.showMessageDialog(qi.getPanels(), "End of quiz");
            //switch to end panel to show results of quiz
        }
    }

    public int randQuestion() {
        random = new Random();
        randIndex = random.nextInt(questions.size());
        return randIndex;
    }
 // .... the rest I left out here because it is not needed for this little test
}

QuizTester (only needs the main method)

public class QuizTester {

    public static void main(String[] args) {
        ArrayList<String> questions = new ArrayList<>(); //as you can see I replaced the List with a list of Strings (because I didn't have your Question class)

        // so these are only strings... 
        questions.add("____________ is the ability of an object to take many forms.");
        questions.add("The process where one object acquires the properties of another is called __________");
        questions.add("The ___________ keyword is used by classes to inherit from interfaces");
        questions.add("Which programming technique can be used to prevent code and data from being randomly accessed by other code defined outside the class?");

        // here I create the QuizSetUp instance and pass the list right with the constructor
        QuizSetUp theQuiz = new QuizSetUp(questions);
        // if everything works out, calling this method 
        // should pick a new question, set it to the QuizInterface
        // and the QuizInterface (the helper version I made) will print it out
        theQuiz.pickQuestion(); 
    }
}

Those three classes can compile as they are and when I ran the program I got this output

question text = The ___________ keyword is used by classes to inherit from interfaces

I know this is a lot different from what you have, the only big change I did was passing the newly create questions list directly to the QuizSetUp instance – so no accessing any static lists.

Answer 2

Looking at this line:

qi.getQuText().setText(getQuestionList().get(randIndex).getQuestionText());

where is the getQuestionList() implemented? It looks like a method call, except that QuizSetUp doesn't declare a getQuestionList() method. It is in a different class.

Conclusion: the code that you've shown us in the question won't even compile.

---

I should point that this (in QuezSetup) is very bad style, dnd liable to cause confusion.

private static ArrayList<Question> questions;

public ArrayList<Question> getQuestionList() {
        return this.questions;
}

While this.questions looks like it is referring to an instance variable, it is actually referring to a static variable. The this is misleading.