Android programming: Banner Ads for minSdkVersion 16

1. In app/build.gradle, add the following in the dependencies (Note: for Google Mobile Ads SDK version 17.0.0, more steps will be needed.):
implementation 'com.google.android.gms:play-services-ads:16.0.0'

2. Create an AdsBanner class:
import android.content.Context;
import android.view.ViewGroup.LayoutParams;

import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdSize;
import com.google.android.gms.ads.AdView;

public class AdsBanner {
    private static final String AD_ID = "ca-app-pub-3940256099942544/6300978111";   // Banner Test Admob ID
    private AdView mAdView;

    public AdsBanner(Context context) {
        mAdView = new AdView(context);
        mAdView.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
        mAdView.setAdSize(AdSize.SMART_BANNER);
        mAdView.setAdUnitId(AD_ID);
    }

    public AdView getAdView() {
        return mAdView;
    }

    public void load() {
        if (mAdView != null) {
            AdRequest adRequest = new AdRequest.Builder()
                    //.addTestDevice(TEST_DEV_HASH)
                    .build();

            mAdView.loadAd(adRequest);
        }
    }
}

3. Add a layout widget as the banner ads container to the Activity:
    <LinearLayout
        android:id="@+id/adLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
    </LinearLayout>


4. Add the following code in the onCreate() method of the Activity to show the banner ads:
        // create AdsBanner unit and append it to the layout.
        AdsBanner adsBanner = new AdsBanner(this);

        LinearLayout llayout = findViewById(R.id.adLayout);
        llayout.addView(adsBanner.getAdView());

        adsBanner.load();