public class CustomActivity extends Activity {

    private NativeAdViewAppWall nav_aw;
    private Button showNative;
    private String appKey = "your_app_key";

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

    private void initializeNativeAds() {
        Appodeal.disableLocationPermissionCheck();
        Appodeal.setAutoCacheNativeIcons(true);
        Appodeal.setAutoCacheNativeMedia(false);
        Appodeal.setTesting(true);
        Appodeal.initialize(this, appKey, Appodeal.NATIVE);

        Appodeal.setNativeCallbacks(new NativeCallbacks() {
            @Override
            public void onNativeLoaded() {
                Log.d("Appodeal", "onNativeLoaded");
            }

            @Override
            public void onNativeFailedToLoad() {
                Log.d("Appodeal", "onNativeFailedToLoad");
            }

            @Override
            public void onNativeShown(NativeAd nativeAd) {
                Log.d("Appodeal", "onNativeShown");
            }

            @Override
            public void onNativeClicked(NativeAd nativeAd) {
                Log.d("Appodeal", "onNativeClicked");
            }
        });

        nav_aw = findViewById(R.id.native_ad_view_app_wall);
        showNative = findViewById(R.id.btn_show);

        showNative.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                showNative();
            }
        });
    }

    void showNative() {
        if (Appodeal.isLoaded(Appodeal.NATIVE)) {
            NativeAd mNativeAd = Appodeal.getNativeAds(1).get(0);
            nav_aw.setNativeAd(mNativeAd);
        }
    }
}