Android : Webview.loadurl from another class

I've set up my webview like this

public class Webview extends Activity {

private WebView webView;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_webview);
    webView = (WebView) findViewById(R.id.webview);
    webView.getSettings().setJavaScriptEnabled(true);
    webView.setWebViewClient(new WebViewClient());

}

and i have another class MainActivity like that

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main); 
}

public void ButtonOnClick(View v) {

      switch(v.getId()) {

        case R.id.button1:
        webView.loadUrl("http://www.google.fr");
        break;      
        case R.id.button2:
        webView.loadUrl("http://www.google.fr");
        break;

       //and so on....
      }
    }

}

here is an extract of mainactivity layout :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/bg"
   android:id="@+id/frontpage_view"
android:tag="front"
 >

   <LinearLayout
    android:id="@+id/linearLayout1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="150dp"
    android:paddingRight="10dp"
    android:orientation="horizontal" >

    <Button
        android:id="@+id/button1"
        android:layout_width="80dip"
        android:layout_height="wrap_content"
        android:layout_marginRight="15dp"
        android:drawableTop="@drawable/actualites"
        android:onClick="ButtonOnClick"
        android:text="Actualités"
        android:textColor="#fff"
        android:textSize="12sp"
        android:textStyle="bold"
        android:typeface="normal"
        android:background="@null"
         />

    <Button
        android:id="@+id/button2"
        android:layout_width="80dip"
        android:layout_height="wrap_content"
        android:drawableTop="@drawable/agenda"
        android:text="Agenda"
        android:onClick="ButtonOnClick"
        android:textColor="#fff"
        android:textSize="12sp"
        android:textStyle="bold"
        android:typeface="normal"
        android:layout_marginRight="15dp"
        android:background="@null" />

I've got he message webview cannot be resolved , do i need to declare the webview in themainactivity too ? how would i do that?