How to set text color for all the elements from an ArrayList in Java?

Question

I have created programmatically, 5 radio groups with 4 radio buttons each. Every radio button represents an answer to a question. So i want to do this. When someone checks the correct answers from the radio groups, i want to add all of them in an ArrayList named correctAnswerRadios. Same with the wrong answers. I set also a OnClickListener on a button. I want also to make all the correct answers green and the wrong answers red, when someone presses the button. With this code, i get this error: 'java.lang.NullPointerException: Attempt to write to null array'.

Here is my code:

RadioGroup[] answerGroup;
RadioButton[] answer;
Button finishButton;
RadioButton[] checkedRadioButton;
ArrayList<RadioButton> correctAnswerRadios;
ArrayList<RadioButton> wrongAnswersRadios;

    correctAnswerRadios = new ArrayList<>();
    wrongAnswersRadios = new ArrayList<>();
    answerGroup = new RadioGroup[5];
    answer = new RadioButton[4];

    int i = 0;
    for (Question qn : questions) {
        answerGroup[i] = new RadioGroup(this);
        int j = 0;
        for (Answer an : answers) {
            if (qn.getID() == an.getQuestion_id_answer()) {
                answer[j] = new RadioButton(this);
                answer[j].setText(an.getAnswer());
                answer[j].setId(j + 100);
                answer[j].setTag(String.valueOf(an.getCorrect_answer()));
                answerGroup[i].addView(answer[j]);

                answer[j].setOnClickListener(new View.OnClickListener() {
                    private boolean isChecked = true;
                    @Override
                    public void onClick(View v) {
                        for (int j = 0; j < answer.length; j++) {
                            checkedRadioButton[j] = ((RadioButton) v);
                            int CorrectAnswer = Integer.parseInt(checkedRadioButton[j].getTag().toString());
                            if (checkedRadioButton[j].isChecked() & CorrectAnswer == 1) {
                                correctAnswerRadios.add(checkedRadioButton[j]);
                            } else {
                                wrongAnswersRadios.add(checkedRadioButton[j]);
                            }
                        }
                    }
                });
                j++;
            }
        }
        linearLayout.addView(answerGroup[i]);
        i++;
    }

    finishButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            for (int i = 0; i < answerGroup.length; i++) {
                for (int j = 0; j < answer.length; j++) {
                    RadioButton correctRadio = correctAnswerRadios.get(j);
                    correctRadio.setTextColor(Color.GREEN);
                    RadioButton wrongRadio = wrongAnswersRadios.get(j);
                    wrongRadio.setTextColor(Color.RED);
                    answerGroup[i].getChildAt(j).setEnabled(false);
                }
            }
        }
    });

Any help will be appreciated .Thanks!

Answer 1

Init checkedRadioButton like

checkedRadioButton = new RadioButton[size];

and change your finishButton listener method to

 public void onClick(View v) {

//Disable buttons
 for (int i = 0; i < answerGroup.length; i++) {
    for (int j = 0; j < answer.length; j++) {

         answerGroup[i].getChildAt(j).setEnabled(false);

     }
 }
 //put button colors

 for(RadioButton correct: correctAnswerRadios){
  correct.setTextColor(Color.GREEN);
 }

 for(RadioButton wrong: wrongAnswersRadios){
  wrong.setTextColor(Color.RED);
 }
}

Answer 2

You need to initialize your array. For instance:

checkedRadioButton = new RadioButton[size];