MainActivity

package com.wallpaper.apcoding.admob;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

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

public class MainActivity extends AppCompatActivity {

    private AdView mAdview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // id admob
        MobileAds.initialize(this, "ca-app-pub-3940256099942544~3347511713");
        // source code banner
        mAdview= findViewById(R.id.adView);
        AdRequest adRequest = new AdRequest.Builder().build();
        mAdview.loadAd(adRequest);
        AdView adView =  new AdView(this);
        adView.setAdSize(AdSize.BANNER);
        adView.setAdUnitId("ca-app-pub-3940256099942544/6300978111");

    }
}