preventing a user from entering multiple answer

i create a true/false quiz app. in that app i have 4 buttons i.e True,False,previous(to get back to previous question),next(to get the next question). i want to add a functionality when a user click on true or false button its get disable for that question so the user can click only once for one question.

i tried to disable the button by using button.setEnabled(false) but when i click on previous button or next button the true/false buttons enabled.i want that the user can click the answer only once it does not matter how much the user traverse the question.

i try to call the setEnabledButton() in previous on click button but it disable the button but it also disable whether the user click on answer or not.

Button btrue,bfalse,bnext,bprevious;
TextView tquestion;
int mCurrentIndex=0;
Questions[] questionbank;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btrue=findViewById(R.id.true_button);
bfalse=findViewById(R.id.false_button);
bnext=findViewById(R.id.next_button);
tquestion=findViewById(R.id.question_text);
bprevious=findViewById(R.id.previous_button);
questionbank = new Questions[]
{
new Questions(R.string.greater,false),
new Questions(R.string.Pm,true),
new Questions(R.string.capital,true),
new Questions(R.string.china,false),
new Questions(R.string.Richer,false),
new Questions(R.string.company,true),
new Questions(R.string.company1,false),
};
update();
bnext.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
int s=questionbank.length;
if( mCurrentIndex<=s  )
{
if (mCurrentIndex + 1 < questionbank.length) {
mCurrentIndex++;
}
else
{   Toast.makeText(getApplicationContext(),"not more question",Toast.LENGTH_SHORT).show();
}
update();
}
}
});
btrue.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
checkAnswer(true);
}
});
bfalse.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
checkAnswer(false);
}
});
bprevious.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (mCurrentIndex > 0) {
mCurrentIndex = (mCurrentIndex - 1);
update();
}
else
{ Toast.makeText(getApplicationContext(), "cant go back", Toast.LENGTH_SHORT).show(); }
}
});
}
public void update()
{
int ques = questionbank[mCurrentIndex].getmTextResid();
tquestion.setText(ques);
setButtonEnabled(true);
}
private void checkAnswer(boolean userPressedTrue)
{
boolean answerIsTrue =
questionbank[mCurrentIndex].ismTrueAnswer();
int messageResId = 0;
if (userPressedTrue == answerIsTrue) {
setButtonEnabled(false);
messageResId = R.string.correct_toast;
} else {
setButtonEnabled(false);
messageResId = R.string.incorrect_toast;
}
Toast.makeText(this, messageResId,
Toast.LENGTH_SHORT)
.show();
}
private void setButtonEnabled(boolean enabled) {
btrue.setEnabled(enabled);
bfalse.setEnabled(enabled);
}

}

In Questions class you can create a method,

public class Questions {
boolean isQuestionAnswered;
public boolean isQuestionAnswered() {
return isQuestionAnswered;
}
public void setQuestionAnswered(boolean questionAnswered) {
isQuestionAnswered = questionAnswered;
}
}

private void checkAnswer(boolean userPressedTrue)
{
questionbank[mCurrentIndex].setQuestionAnswered(true);    
boolean answerIsTrue =
questionbank[mCurrentIndex].ismTrueAnswer();
int messageResId = 0;
if (userPressedTrue == answerIsTrue) {
setButtonEnabled(false);
messageResId = R.string.correct_toast;
} else {
setButtonEnabled(false);
messageResId = R.string.incorrect_toast;
}
Toast.makeText(this, messageResId,
Toast.LENGTH_SHORT)
.show();
}

public void update()
{
int ques = questionbank[mCurrentIndex].getmTextResid();
tquestion.setText(ques);
if(questionbank[mCurrentIndex].isQuestionAnswered())
setButtonEnabled(false);
else
setButtonEnabled(true);
}

Try this out and check whether this solves your problem