videoAd.setRewardedVideoAdListener(this);

// Required to reward the user.
@Override
public void onRewarded(RewardItem reward) {
      Toast.makeText(this, "onRewarded! currency: " + reward.getType() + "  amount: " +
                reward.getAmount(), Toast.LENGTH_SHORT).show();
     // Reward the user.
}

@Override
public void onRewardedVideoAdLeftApplication() {
    Toast.makeText(this, "onRewardedVideoAdLeftApplication",
            Toast.LENGTH_SHORT).show();
}

@Override
public void onRewardedVideoAdClosed() {
    Toast.makeText(this, "onRewardedVideoAdClosed", Toast.LENGTH_SHORT).show();
    videoAd.destroy(this);
}