Am a beginner in Android, I got this this source code for Quiz online, it works perfectly but am trying to modified with my taste.The issues am facing is allowing users to click on previous button to get previous question selected but don't know how to go about it 


here is the code, Help 



package com.onlineicttutor.ictquiz;

import android.content.Intent;
import android.support.v4.app.NavUtils;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.u
Am a beginner in Android, I got this this source code for Quiz online, it works perfectly but am trying to modified with my taste.The issues am facing is allowing users to click on previous button to get previous question selected but don't know how to go about it 


here is the code, Help 
package com.onlineicttutor.ictquiz;

import android.content.Intent;
import android.support.v4.app.NavUtils;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;

import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;
import com.onlineicttutor.ictquiz.db.DBAdapter;
import com.onlineicttutor.ictquiz.model.Question;

import java.util.ArrayList;
import java.util.List;

public class ConceptActivity extends AppCompatActivity {

    private List<Question> questionsList;
    private Question currentQuestion;

    private TextView txtQuestion,tvNoOfQs;
    private RadioButton rbtnA, rbtnB, rbtnC,rbtnD;
    private Button btnNext,btnPrev;

    private int obtainedScore=0;
    private int questionId=0;

    private int answeredQsNo=0;

    ArrayList<String> myAnsList;


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

  


        //Initialize the view
        init();

        //Initialize the database
        final DBAdapter dbAdapter=new DBAdapter(this);
        questionsList= dbAdapter.getAllQuestions();
        currentQuestion=questionsList.get(questionId);

        //Set question
        setQuestionsView();

        //Check and Next
        btnNext.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                RadioGroup grp=(RadioGroup)findViewById(R.id.radioGroup1);
                RadioButton answer = (RadioButton)findViewById(grp.getCheckedRadioButtonId());

                Log.e("Answer ID", "Selected Positioned  value - "+grp.getCheckedRadioButtonId());

                if(answer!=null){
                    Log.e("Answer", currentQuestion.getANSWER() + " -- " + answer.getText());
                    //Add answer to the list
                    myAnsList.add(""+answer.getText());

                    if(currentQuestion.getANSWER().equals(answer.getText())){
                        obtainedScore++;
                        Log.e("comments", "Correct Answer");
                        Log.d("score", "Obtained score " + obtainedScore);
                    }else{
                        Log.e("comments", "Wrong Answer");
                    }
                    if(questionId<dbAdapter.rowCount()){
                        currentQuestion=questionsList.get(questionId);
                        setQuestionsView();
                    }else{
                        Intent intent = new Intent(ConceptActivity.this, ResultActivity.class);

                        Bundle b = new Bundle();
                        b.putInt("score", obtainedScore);
                        b.putInt("totalQs", questionsList.size());
                        b.putStringArrayList("myAnsList", myAnsList);
                        intent.putExtras(b);
                        startActivity(intent);
                        finish();

                    }

                }else{
                    Log.e("comments", "No Answer");
                }

                //Need to clear the checked item id
                grp.clearCheck();


            }//end onClick Method
        });
  //Prev Button
         btnPrev.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //Showing previous,choosed question ;

            }
        });
    }

    public void init(){
        tvNoOfQs=(TextView)findViewById(R.id.tvNumberOfQuestions);
        txtQuestion=(TextView)findViewById(R.id.tvQuestion);
        rbtnA=(RadioButton)findViewById(R.id.radio0);
        rbtnB=(RadioButton)findViewById(R.id.radio1);
        rbtnC=(RadioButton)findViewById(R.id.radio2);
        rbtnD=(RadioButton)findViewById(R.id.radio3);

        btnNext=(Button)findViewById(R.id.btnNext);

        myAnsList = new ArrayList<String>();
    }


    private void setQuestionsView()
    {
        rbtnA.setChecked(false);
        rbtnB.setChecked(false);
        rbtnC.setChecked(false);
        rbtnD.setChecked(false);

        answeredQsNo=questionId+1;
        tvNoOfQs.setText("Questions "+answeredQsNo+" of "+questionsList.size());

        txtQuestion.setText(currentQuestion.getQUESTION());
        rbtnA.setText(currentQuestion.getOptionA());
        rbtnB.setText(currentQuestion.getOptionB());
        rbtnC.setText(currentQuestion.getOptionC());
        rbtnD.setText(currentQuestion.getOptionD());

        questionId++;
    }


    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            // Respond to the action bar's Up/Home button
            case android.R.id.home:
                NavUtils.navigateUpFromSameTask(this);
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}