Null pointer exception in android google maps

I'm trying to add google maps to my app. The logcat window shows this error: Caused by: java.lang.NullPointerException at com.example.mymaps.MainActivity.onCreate(MainActivity.java:27) at android.app.Activity.performCreate(Activity.java:5104) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080).

How to remove this error?

   Main xml:
   <RelativeLayout     
   xmlns:android="http://ift.tt/nIICcg"
   xmlns:tools="http://ift.tt/LrGmb4"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity" >

  <fragment
    android:id="@+id/map"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    class="com.google.android.gms.maps.MapFragment" />

 </RelativeLayout>

Main Java import android.app.Activity; import android.os.Bundle; import android.view.Menu;

  import com.google.android.gms.maps.CameraUpdateFactory;

  import com.google.android.gms.maps.GoogleMap;
  import com.google.android.gms.maps.MapFragment;
  import com.google.android.gms.maps.model.BitmapDescriptorFactory;
  import com.google.android.gms.maps.model.LatLng;
  import com.google.android.gms.maps.model.Marker;
  import com.google.android.gms.maps.model.MarkerOptions;

  public class MainActivity extends Activity {
  static final LatLng HAMBURG = new LatLng(53.558, 9.927);
  static final LatLng KIEL = new LatLng(53.551, 9.993);
  private GoogleMap map;

   @Override
   protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
     map = ((MapFragment) getFragmentManager().findFragmentById(R.id.map))
    .getMap();
     Marker hamburg = map.addMarker(new MarkerOptions().position(HAMBURG)
    .title("Hamburg"));
     Marker kiel = map.addMarker(new MarkerOptions()
    .position(KIEL)
    .title("Kiel")
    .snippet("Kiel is cool")
    .icon(BitmapDescriptorFactory
        .fromResource(R.drawable.ic_launcher)));

    // Move the camera instantly to hamburg with a zoom of 15.
    map.moveCamera(CameraUpdateFactory.newLatLngZoom(HAMBURG, 15));

    // Zoom in, animating the camera.
   map.animateCamera(CameraUpdateFactory.zoomTo(10), 2000, null);
   }

    @Override
   public boolean onCreateOptionsMenu(Menu menu) {
   getMenuInflater().inflate(R.menu.activity_main, menu);
   return true;
   }

  } 

LogCat window:

08-13 23:32:27.279: E/AndroidRuntime(1010): FATAL EXCEPTION: main 08-13 23:32:27.279: E/AndroidRuntime(1010): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mymaps/com.example.mymaps.MainActivity}: java.lang.NullPointerException 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.app.ActivityThread.access$600(ActivityThread.java:141) 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.os.Handler.dispatchMessage(Handler.java:99) 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.os.Looper.loop(Looper.java:137) 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.app.ActivityThread.main(ActivityThread.java:5039) 08-13 23:32:27.279: E/AndroidRuntime(1010): at java.lang.reflect.Method.invokeNative(Native Method) 08-13 23:32:27.279: E/AndroidRuntime(1010): at java.lang.reflect.Method.invoke(Method.java:511) 08-13 23:32:27.279: E/AndroidRuntime(1010): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 08-13 23:32:27.279: E/AndroidRuntime(1010): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 08-13 23:32:27.279: E/AndroidRuntime(1010): at dalvik.system.NativeStart.main(Native Method) 08-13 23:32:27.279: E/AndroidRuntime(1010): Caused by: java.lang.NullPointerException 08-13 23:32:27.279: E/AndroidRuntime(1010): at com.example.mymaps.MainActivity.onCreate(MainActivity.java:27) 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.app.Activity.performCreate(Activity.java:5104) 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 08-13 23:32:27.279: E/AndroidRuntime(1010): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 08-13 23:32:27.279: E/AndroidRuntime(1010): ... 11 more

via Chebli Mohamed