Interstitial ad

public class MainActivity extends ActionBarActivity
{
    private static final String ADMOB_INTERSTITIAL_UNIT_ID = "ca-app-pub-XXXXXXXXXXXXXXXXXXXXXXXXXXX";

    private InterstitialAd mInterstitialAd;


    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);

        ...

        // admob
        mInterstitialAd = new InterstitialAd(this);
        mInterstitialAd.setAdUnitId(ADMOB_INTERSTITIAL_UNIT_ID);
        mInterstitialAd.setAdListener(new AdListener()
        {
            @Override
            public void onAdClosed()
            {
                finish();
            }
        });
        requestNewInterstitial();
    }


    @Override
    public void onBackPressed()
    {
        if(mInterstitialAd.isLoaded())
        {
            mInterstitialAd.show();
        }
        else
        {
            finish();
        }
    }


    private void requestNewInterstitial()
    {
        AdRequest adRequest = new AdRequest.Builder().addTestDevice(getString(R.string.admob_test_device_id)).build();
        mInterstitialAd.loadAd(adRequest);
    }
}