答案正确时，Android测验应用程序不正确

我正在尝试开发一个测验应用程序，在其中我手动编写一系列问题和答案，然后使用它们来设置单选按钮和文本视图的文本值。但是，当我尝试运行它并对其进行操作时，在第一个问题集上就很好了，然后下一个正确的答案就变得不正确了，反之亦然。下面的截图。

当我按下正确的一个正确的。

不正确的一个，但是我按了正确的一个（您知道答案）。

It seems to me that the first set of question's values were not moved. I tried everything I can think of but no luck. I see what happens in my logcat when I tried to print out the current text. Here's a snippet from my logcat.

04-24 01:56:10.880 4093-4093/com.example.muhammad.exquizme D/answer: Google
04-24 01:56:10.880 4093-4093/com.example.muhammad.exquizme D/correctAnswer: Google
04-24 01:56:10.885 4093-4093/com.example.muhammad.exquizme D/Is it correct?: Correct
04-24 01:56:10.894 4093-4147/com.example.muhammad.exquizme W/OpenGLRenderer: Fail to change FontRenderer cache size, it already initialized
04-24 01:56:32.322 4093-4093/com.example.muhammad.exquizme D/answer: Google
04-24 01:56:32.322 4093-4093/com.example.muhammad.exquizme D/correctAnswer: An algorithm
04-24 01:56:32.326 4093-4093/com.example.muhammad.exquizme D/Is it correct?: Incorrect

Here's the code for that part.

QuizQuestion[] questionArray; //global variable
    int randomIndex;//global variable

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

        qIndexView = (TextView) findViewById(R.id.currentNumber);
        questionTextView = (TextView) findViewById(R.id.questionTextView);
        choiceBtnA = (RadioButton) findViewById(R.id.choiceA);
        choiceBtnB = (RadioButton) findViewById(R.id.choiceB);
        choiceBtnC = (RadioButton) findViewById(R.id.choiceC);
        choiceBtnD = (RadioButton) findViewById(R.id.choiceD);
        questionArray = new QuizQuestion[5];

        displayQuestion();


        final String a = choiceBtnA.getText().toString();
        final String b = choiceBtnB.getText().toString();
        final String c = choiceBtnC.getText().toString();
        final String d = choiceBtnD.getText().toString();

        choiceBtnA.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                checkAnswers(a);
                final Handler handler = new Handler();
                handler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        displayQuestion();
                    }
                }, 2000);

                //displayQuestion();
            }
        });

        choiceBtnB.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                checkAnswers(b);
                final Handler handler = new Handler();
                handler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        displayQuestion();
                    }
                }, 2000);
            }
        });

        choiceBtnC.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                checkAnswers(c);
                final Handler handler = new Handler();
                handler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        displayQuestion();
                    }
                }, 2000);
            }
        });

        choiceBtnD.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                checkAnswers(d);
                final Handler handler = new Handler();
                handler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        displayQuestion();
                    }
                }, 2000);
            }
        });
    }

//This is called every pressed
public void displayQuestion() {

        //Create Question list
        String theQuestion = "Android mobile operating system was released on 23rd September 2008 developed by who?";
        String[] choices = new String[]{"Google", "IBM", "Intel", "Oracle"};
        questionArray[0] = new QuizQuestion(theQuestion, choices, choices[0], "Computing History");

        theQuestion = "Who invented the programming language called 'Java'?";
        choices = new String[]{"James Gosling", "Steve Jobs", "Bill Gates", "Elon Musk"};
        questionArray[1] = new QuizQuestion(theQuestion, choices, choices[0], "Computing History");

        theQuestion = "Which of the following languages is more suited to a structured program?";
        choices = new String[]{"FORTRAN", "BASIC", "PASCAL", "None of the above"};
        questionArray[2] = new QuizQuestion(theQuestion, choices, choices[3], "Computer Fundamentals");

        theQuestion = "The brain of any computer system is";
        choices = new String[]{"Memory", "ALU", "CPU", "Control unit"};
        questionArray[3] = new QuizQuestion(theQuestion, choices, choices[2], "Computer Fundamentals");

        theQuestion = "The step-by-step instructions that solve a problem are called _____.";
        choices = new String[]{"An algorithm", "A list", "A plan", "A sequential structure"};
        questionArray[4] = new QuizQuestion(theQuestion, choices, choices[0], "System Analysis and Design");

        randomIndex = new Random().nextInt(questionArray.length);

        questionTextView.setText(questionArray[randomIndex].question);
        choiceBtnA.setText(questionArray[randomIndex].choices[0]);
        choiceBtnB.setText(questionArray[randomIndex].choices[1]);
        choiceBtnC.setText(questionArray[randomIndex].choices[2]);
        choiceBtnD.setText(questionArray[randomIndex].choices[3]);

    }

//checks answer when clicked
public boolean checkAnswers(String answer) {
        Log.d("answer", answer);
        String correctAnswer = questionArray[randomIndex].answer;
        Log.d("correctAnswer", correctAnswer);
        if (answer.equals(correctAnswer)) {
            Toast.makeText(PlayQuizActivity.this, "Correct", Toast.LENGTH_SHORT).show();
            Log.d("Is it correct?", "Correct");
            return true;
        } else {
            Toast.makeText(PlayQuizActivity.this, "Incorrect", Toast.LENGTH_SHORT).show();
            Log.d("Is it correct?", "Incorrect");
        }

        return false;
}

That's all I have at the moment. Let me know if you need clarification coz my english is not that good. Thanks in advance.