Exception we have null reference object but the radio button is initialized

I have been blocked for 2 days, I have an exception on a radio button for a change of language of the application, activity stop with nullPointerException on a null objet reference,

“NullPointerException: Attempt to invoke virtual method ‘void android.widget.RadioGroup.setOnCheckedChangeListener(android.widget.RadioGroup$OnCheckedChangeListener)’ on a null object reference”

strings file xml are ok, do you see something that I do not see? here is the code :

public class ArtistActivity extends AppCompatActivity implements View.OnClickListener {

TextView name;
ImageView img;
TextView music;
String title;
String musicArtist;
MaterialButton btnPlay;
MaterialButton btnStop;
TextView titleMusicArtist;
MediaPlayer mediaPlayer = new MediaPlayer();
RadioGroup rdioGrp;

// information artist
String imgUrl = "https://st3.depositphotos.com/1008939/12603/i/950/depositphotos_126032722-stock-photo-roaring-singing-woman.jpg";
String musicUrl = "https://www.soundhelix.com/examples/mp3/SoundHelix-Song-4.mp3";
String siteUrl = "https://sites.google.com/view/bestrecord/accueil?authuser=1";

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


    // button music, playlist and new playlist
    LinearLayout linearPlaylist = findViewById(R.id.linearPlaylist);
    LinearLayout linearNewPlaylist = findViewById(R.id.linearNewPlaylist);
    LinearLayout linearMusic = findViewById(R.id.linearMusic);
    linearPlaylist.setOnClickListener(this);
    linearNewPlaylist.setOnClickListener(this);
    linearMusic.setOnClickListener(this);
    linearMusic.setTag(0);
    linearPlaylist.setTag(1);
    linearNewPlaylist.setTag(2);

    // button play
    btnPlay = findViewById(R.id.btn_play_music_artist);
    btnPlay.setOnClickListener(this);
    btnPlay.setTag(3);

    // button stop
    btnStop = findViewById(R.id.btn_stop_music_artist);
    btnStop.setOnClickListener(this);
    btnStop.setTag(4);

    // textView title Music
    titleMusicArtist = findViewById(R.id.txtLastMusicPlayed);

    // display artist information
    name = findViewById(R.id.txtViewTitleArtist);
    img = findViewById(R.id.imageArtist);
    music = findViewById(R.id.txtViewMusicArtist);


    // image artiste
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);

    try {
        InputStream input = new java.net.URL(imgUrl).openStream();
        Bitmap bitmap = BitmapFactory.decodeStream(input);
        img.setImageBitmap(bitmap);
    } catch (IOException e) {
        e.printStackTrace();
    }

    // name and song title artist
    Scrap scrapTitle = new Scrap();
    scrapTitle.execute();


    // prepare music artist
    if (!mediaPlayer.isPlaying()) {
        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
        try {
            mediaPlayer.setDataSource(musicUrl);
            mediaPlayer.prepare();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // language configuration
    init();

}



// scrap information artist
@SuppressLint("StaticFieldLeak")
private class Scrap extends AsyncTask<Void, Void, Void> {

@Override
protected void onPreExecute() {
    super.onPreExecute();
}

@Override
protected Void doInBackground(Void... voids) {

    Document document = null;
    try {
        // Connect to the website
        document = Jsoup.connect(siteUrl).get();

    } catch (IOException e) {
        e.printStackTrace();
    }
    // take name artist
    assert document != null;
    List<String> e = document.getElementsByClass(" jgG6ef").eachText();
    title = e.get(0)+" "+e.get(1);
    name.setText(title);

    // take song title artist
    List<String> ee = document.getElementsByAttributeValue("id","h.s0qhywz0cts2").eachText();
    musicArtist = ee.get(0);
    music.setText(musicArtist);
    return null;
}

@Override
protected void onPostExecute(Void aVoid) { }
}

// create menu application
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    super.onCreateOptionsMenu(menu);
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu_mainactivity, menu);
    return true;
}

// menu buttons music / playlist / new playlist
public void onClick(View v) {
    int btnInt = ( int ) v.getTag();

    // button music clicked
    if ( btnInt == 0 ) {
        // go to page music
        Intent musicIntent = new Intent(ArtistActivity.this, MainActivity.class );
        startActivity( musicIntent );

    // button playlist clicked
    } else if ( btnInt == 1 ) {
        // go to page playlist
        Intent PlaylistIntent = new Intent(ArtistActivity.this, PlaylistActivity.class );
        startActivity( PlaylistIntent );

    // button new playlist clicked
    }else if ( btnInt == 2 ) {
        // go to page new playlist
        Intent newPlaylistIntent = new Intent(ArtistActivity.this, NewPlaylistActivity.class );
        startActivity( newPlaylistIntent );
    }
    // end menu button


    // button play/pause
    else if( btnInt == 3) {
        if(mediaPlayer.isPlaying()) {
            mediaPlayer.pause();
            btnPlay.setIconResource(R.drawable.ic_baseline_play_arrow_24);
        } else if(!mediaPlayer.isPlaying()) {
            mediaPlayer.start();
            if(mediaPlayer.isPlaying()) btnPlay.setIconResource(R.drawable.ic_pause);
        }
    }
    // button stop
    else if( btnInt == 4) {
        mediaPlayer.reset();
        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
        try {
            mediaPlayer.setDataSource(musicUrl);
            mediaPlayer.prepare();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


}

// menu hamburger, items clicked
@SuppressLint("NonConstantResourceId")
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();
    switch (id){
        case R.id.artiste:
            Toast.makeText(ArtistActivity.this, item.getTitle().toString(), Toast.LENGTH_SHORT).show();
            break;

        case R.id.site_officiel:
            Intent intent = new Intent(Intent.ACTION_VIEW).setData(Uri.parse("https://sites.google.com/view/bestrecord/accueil?authuser=1"));
            startActivity(intent);
            break;

        case R.id.contact:
            Intent contactIntent = new Intent(ArtistActivity.this, ContactBestRecord.class );
            startActivity( contactIntent );
            break;

        case R.id.langue:
            AlertDialog.Builder alertLang = new AlertDialog.Builder( this );
            alertLang.setView( R.layout.layout_test )
                    .create()
                    .show();
            break;

        case R.id.about:
            AlertDialog.Builder alert = new AlertDialog.Builder( this );
            alert.setView( R.layout.about_us )
                    .create()
                    .show();
            break;
    }
    return super.onOptionsItemSelected(item);
}
// end menu



// change language
public void init() {
    rdioGrp = findViewById(R.id.rdioGrpLang);
    rdioGrp.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
        @SuppressLint("NonConstantResourceId")
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {
            RadioButton rb = (RadioButton) group.findViewById(checkedId);
            if (rb!=null){
                switch(checkedId) {
                    case R.id.radioBtnFr:
                        changeLang("fr");
                        break;

                    case R.id.radioBtnEn:
                        changeLang("en");
                        break;

                    case R.id.radioBtnIt:
                        changeLang("it-rIT");
                        break;

                    default:
                        changeLang("fr");
                }

            }
        }
    });

}

// method to change language
public void changeLang(String l) {
    Locale locale = new Locale(l);
    Locale.setDefault(locale);
    Configuration config = new Configuration();
    config.locale = locale;
    getBaseContext().getResources().updateConfiguration(config, getBaseContext().getResources().getDisplayMetrics());
    recreate();
}
}

the layout call in dialBox layout “test” :

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/border_layout_about_us"
android:padding="@dimen/dim_15">

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/chooseLanguage"
    android:textColor="@color/white"
    android:textSize="@dimen/dim_20"
    android:gravity="center"
    tools:ignore="SpUsage"
    android:id="@+id/txtLangue"/>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/txtLangue"
    android:orientation="horizontal"
    android:gravity="center"
    >


    <RadioGroup
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:layout_margin="@dimen/dim_10"
        android:id="@+id/rdioGrpLang"
        tools:ignore="UselessParent">

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/radioBtnFr"
            android:checked="true"
            android:buttonTint="@color/white"
            android:textColor="@color/white"
            android:text="@string/langueFr">
        </RadioButton>

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/radioBtnEn"
            android:text="@string/langueEn"
            android:buttonTint="@color/white"
            android:textColor="@color/white"
            android:layout_marginLeft="@dimen/dim_10"
            android:layout_marginRight="@dimen/dim_10">
        </RadioButton>

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/radioBtnIt"
            android:buttonTint="@color/white"
            android:textColor="@color/white"
            android:text="@string/langueIt">
        </RadioButton>

    </RadioGroup>

</LinearLayout>

Answer

Delete -//language configuration- In Your Code And

Edit The onOptionsItemSelected method as follows:

@SuppressLint("NonConstantResourceId")
@Override
public boolean onOptionsItemSelected(MenuItem item) {

    ....
    ....
    case R.id.langue:
    AlertDialog alert = new AlertDialog.Builder( this ).setView( R.layout.choose_language).create();
    alert.show();
    rdioGrp = alert.findViewById(R.id.rdioGrpLang);
    setRadioListener();
        break;

    ....
    ....
} // End onOptionsItemSelected Mehtod


private void setRadioListener() {

    rdioGrp.setOnCheckedChangeListener(new 
RadioGroup.OnCheckedChangeListener() {
        @SuppressLint("NonConstantResourceId")
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {
            RadioButton rb = (RadioButton) 
group.findViewById(checkedId);
            if (rb!=null){
                switch(checkedId) {
                    case R.id.radioBtnFr:
                        changeLang("fr");
                        break;

                    case R.id.radioBtnEn:
                        changeLang("en");
                        break;

                    case R.id.radioBtnIt:
                        changeLang("it-rIT");
                        break;

                    default:
                        app.l("iiii");
                }

            }
        }
    });
}

public void changeLang(String l) {
    Locale locale = new Locale(l);
    Locale.setDefault(locale);
    Configuration config = new Configuration();
    config.locale = locale;
    getBaseContext().getResources().updateConfiguration(config, getBaseContext().getResources().getDisplayMetrics());
    recreate();
}