How to put Admob banner in Android Studio

How to add adMob banner in Android Studio

To create an adMob banner using Java copy this code to your MainActivity.java file:
"change your activity name, adView ID and before publishing your App, change your App ID"

public class MainActivity extends AppCompatActivity {
        private AdView mAdView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        MobileAds.initialize(this, "ca-app-pub-3940256099942544~3347511713");
        mAdView = findViewById(R.id.adView);
        AdRequest adRequest = new AdRequest.Builder().build();
        mAdView.loadAd(adRequest);
        //now your admob banner will appears in your activity
    }
}

In the xml file of your activity, add to <android.support.constraint.ConstraintLayout :

    xmlns:ads="http://schemas.android.com/apk/res-auto"

and this code in your RelativeLayout :

<com.google.android.gms.ads.AdView
            android:id="@+id/adView5"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_centerHorizontal="true"
            ads:adSize="SMART_BANNER"
            ads:adUnitId="ca-app-pub-3940256099942544/6300978111"
            android:layout_marginBottom="74dp" />