RewardedAd

abstract class RewardedAd

public class MainActivity extends AppCompatActivity {

    private RewardedAd rewardedAd;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        FullScreenContentCallback fullScreenContentCallback =
            new FullScreenContentCallback() {
                @Override
                public void onAdShowedFullScreenContent() {
                    // Code to be invoked when the ad showed full screen content.
                }

                @Override
                public void onAdDismissedFullScreenContent() {
                    rewardedAd = null;
                    // Code to be invoked when the ad dismissed full screen content.
                }
            };

        RewardedAd.load(
            this,
            "adUnitId",
            new AdRequest.Builder().build(),
            new RewardedAdLoadCallback() {
                @Override
                public void onAdLoaded(RewardedAd ad) {
                    findViewById(R.id.display_button).setVisibility(View.VISIBLE);
                    rewardedAd = ad;
                    rewardedAd.setFullScreenContentCallback(fullScreenContentCallback);
                }
            });
    }

    public void onDisplayButtonClicked(View view) {
        if (rewardedAd != null) {
            rewardedAd.show(
                this,
                new OnUserEarnedRewardListener() {
                    @Override
                    public void onUserEarnedReward(@NonNull RewardItem rewardItem) {
                        Toast.makeText(
                            MainActivity.this,
                            "onRewarded! currency: "
                                + rewardItem.getType() + "    amount: "
                                + rewardItem.getAmount(), Toast.LENGTH_SHORT).show();
                    }
                });
        }
    }
}