Action bar moving down while replacing with fragment

I am adding a fragment to activity, and then i am replacing that fragment with the second fragment.After replacing the second fragment action bar is slightly moving down like this

My Activity code

public class MyActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.meetinglist_activity);
    Fragment first_fragment = new FirstFragment();
    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.add(R.id.content_frame, first_fragment).commit();
     }

Replacing second fragment in the first fragment's button click

public class Firstfragment extends Fragment  {


FloatingActionButton new_fab;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View list_view=inflater.inflate(R.layout.meetingslist_fragment,container,false);
    new_fab=(FloatingActionButton)list_view.findViewById(R.id.meeting_new);
    new_fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Fragment second_fragment = new SecondFragment();
            FragmentTransaction ft =getActivity().getSupportFragmentManager().beginTransaction();
            ft.replace(R.id.content_frame, second_fragment).commit();
  }

Activity layout

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:orientation="vertical" android:layout_width="match_parent"
 android:layout_height="match_parent">
 <FrameLayout
    android:id="@+id/content_frame"
    android:layout_width="match_parent"
    android:layout_height="match_parent"></FrameLayout>
   </LinearLayout>

Fragment's Xml

<!--First Layout-->
<?xml version="1.0" encoding="utf-8"?>
<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:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true">

<android.support.design.widget.FloatingActionButton
    android:id="@+id/meeting_new"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    android:src="@android:drawable/ic_dialog_email" />

    </android.support.design.widget.CoordinatorLayout>


 <!--Second Layout-->

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Large Text"
    android:gravity="center"
    android:id="@+id/textView"
    android:layout_gravity="center_horizontal" />
    </LinearLayout>

I am using android.support.v4.app.Fragment;

I am using Android Studio version2.0 and latest API levels.

Can anybody help me? Thanks in advance.