从内部类内部访问局部变量问题；需要宣布为最终

Question

该程序应使用预设的问题和答案，并检查是否按下了是或否按钮。它有一个主要的活动文件和一个称为Question的类文件，但是运行时，输出显示“错误：从内部类内部访问局部变量问题；需要声明为final”。我修理它？谢谢，在数组列表声明前添加final关键字无效。

    public class MainActivity extends Activity {

    private TextView display_question;
    private TextView display_result;
    private static int rand_int;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Random random = new Random();

        display_question = findViewById(R.id.txt_question);
        display_result = findViewById(R.id.txt_result);
        ArrayList<Question> questions;      //in class method

        questions = Question.getQuestions();    //in class method, arraylist

        rand_int = random.nextInt(4);

        display_question.setText(questions.get(rand_int).getQuestion());// where i is an integer


        Button btn_true = findViewById(R.id.btn_true);
        btn_true.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                boolean input = true;
                String output = "correct answer";
                String output2 = "incorrect answer";
                if (questions.get(rand_int).isAnswer()==input){
                    display_result.setText(output);
                }
                else {
                    display_result.setText(output2);
                }

            }
        });


        Button btn_false = findViewById(R.id.btn_false);
        btn_false.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                boolean input = false;
                String output = "correct answer";
                String output2 = "incorrect answer";
                if (questions.get(rand_int).isAnswer()==input){
                    display_result.setText(output);
                }
                else {
                    display_result.setText(output2);
                }

            }
        });


        Button btn_next = findViewById(R.id.btn_next);
        btn_next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                rand_int = random.nextInt(4);
                display_question.setText(questions.get(rand_int).getQuestion());// where i is an integer


                }
            });

        }

    }

---

问题课：

import java.util.ArrayList;

public class Question {
    private String question;
    private boolean answer;


    private Question(String question, boolean answer) {
        this.question = question;
        this.answer = answer;

    }


    public String getQuestion() {
        return question;
    }

    public boolean isAnswer() {
        return answer;
    }


    public static ArrayList<Question> getQuestions(){

        ArrayList<Question> questions = new ArrayList<>();
        questions.add(new Question("B", false));
        questions.add(new Question("A", true));
        questions.add(new Question("c", false));
        questions.add(new Question("d", false));
        questions.add(new Question("e", true));


    return questions;

    }




}