android studio admob banner doesn't work : <p>I am working on simple android app that contain Admob banner, but when I run the app I get this message:</p>

<pre><code>unfortunately the app has stopped
</code></pre>

<p>here is my code:</p>

<p>xml layout: </p>

<pre><code> &lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/main_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.ajater.mj.vaccalc.MainActivity"
xmlns:ads="http://schemas.android.com/apk/libs/com.google.ads"&gt;


   &lt;com.google.ads.AdView
    xmlns:ads="http://schemas.android.com/apk/libs/com.google.ads"
    android:id="@+id/adView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    ads:loadAdOnCreate="true"
    ads:adSize="BANNER"
    ads:adUnitId="------------------" /&gt;
   &lt;/android.support.design.widget.CoordinatorLayout&gt;
</code></pre>

<p>mainactivity</p>

<pre><code>    AdView adView = (AdView)findViewById(R.id.adView);
    AdRequest adRequest = new AdRequest.Builder().build();
    adView.loadAd(adRequest);
</code></pre>

<p>AndroidManifest</p>

<pre><code>    &lt;?xml version="1.0" encoding="utf-8"?&gt;
    &lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="my.app.name"&gt;
    &lt;uses-permission android:name="android.permission.INTERNET"/&gt;
    &lt;uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/&gt;
</code></pre>
