Existing Native Content Ad API

sample.java

AdLoader adLoader = new AdLoader.Builder(context, "ca-app-pub-3940256099942544/2247696110")
    .forContentAd(new OnContentAdLoadedListener() {
        @Override
        public void onContentAdLoaded(NativeContentAd contentAd) {
            // Show the content ad.
        }
    })
    .withAdListener(new AdListener() {
        @Override
        public void onAdFailedToLoad(int errorCode) {
            // Handle the failure by logging, altering the UI, and so on.
        }
    })
    .withNativeAdOptions(new NativeAdOptions.Builder()
            // Methods in the NativeAdOptions.Builder class can be
            // used here to specify individual options settings.
            .build())
    .build();

adLoader.loadAd(new PublisherAdRequest.Builder().build());