Make a method in onCreate run only once [duplicate]

In my mainActivity I have the method: player.setPlayWhenReady (true) which is responsible for getting the player to start playing and continues to run in the background while I'm browsing between my Activity, the problem occurs when I try to return to my mainActivity the player is played again, thus getting 2 audios playing at the same time.

private Handler mainHandler;
private BandwidthMeter bandwidthMeter;
private TrackSelector trackSelector;
private TrackSelection.Factory trackSelectionFactory;
private LoadControl loadControl;
private SimpleExoPlayer player;
private DataSource.Factory dataSourceFactory;
private ExtractorsFactory extractorsFactory;
private MediaSource mediaSource;

private String radioUrl = "http://audio1.cmaudioevideo.com:8237/stream";


private ImageButton pause;
private ImageButton play;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    play = (ImageButton) findViewById(R.id.play) ;
    pause = (ImageButton) findViewById(R.id.pause) ;


    mainHandler = new Handler();
    bandwidthMeter = new DefaultBandwidthMeter();
    loadControl = new DefaultLoadControl();
    extractorsFactory = new DefaultExtractorsFactory();



    trackSelectionFactory = new AdaptiveVideoTrackSelection.Factory(bandwidthMeter);

    trackSelector = new DefaultTrackSelector(mainHandler,
            trackSelectionFactory);


    dataSourceFactory = new DefaultDataSourceFactory(this,
            Util.getUserAgent(this, "mediaPlayerSample"),
            (TransferListener<? super DataSource>) bandwidthMeter);


    mediaSource = new ExtractorMediaSource(Uri.parse(radioUrl),
            dataSourceFactory,
            extractorsFactory,
            null,
            null);

    player = ExoPlayerFactory.newSimpleInstance(getApplicationContext(),
            trackSelector,
            loadControl);

    player.prepare(mediaSource);

    player.setPlayWhenReady(true);

    Log.v("TEST","playing state : " + player.getPlaybackState());


    play.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            player.setPlayWhenReady(true);
            play.setVisibility(View.GONE);
            pause.setVisibility(View.VISIBLE);

        }
    });

    pause.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            player.setPlayWhenReady(false);
            play.setVisibility(View.VISIBLE);
            pause.setVisibility(View.GONE);
        }
    });

}

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    int id = item.getItemId();
    if (id == R.id.nav_sobre) {
        Intent it_sobre = new Intent(MainActivity.this,SobreActivity.class);
        startActivity(it_sobre);}
    else if (id == R.id.nav_equipe) {
        Intent it_valores = new Intent(MainActivity.this,EquipeActivity.class);
        startActivity(it_valores);}
    else if (id == R.id.nav_contato) {
        Intent it_contato = new Intent(MainActivity.this,ContatoActivity.class);
        startActivity(it_contato);}

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}


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

}