Android : Back button after webview

I've got 2 activities Activity A & Activity B (webview) What i'm trying to do is, when the webview can't go back anymore, it will display Activity A and on press again prompt for exit

Here is Activity A :

import com.jeumont.app.R;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.View;



public class frontpage extends Activity {

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

The webview which contains the backpress function :

public class webview extends Activity {

private WebView webView;
@SuppressLint("SetJavaScriptEnabled") @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //Init Barre de chargement
    final ProgressDialog pd = ProgressDialog.show(this, "", "Chargement en cours", true);
    setContentView(R.layout.activity_webapp);
    webView = (WebView) findViewById(R.id.webView_web_app);
    webView.getSettings().setJavaScriptEnabled(true);
    String url = getIntent().getStringExtra("url");
    webView.loadUrl(url);
    webView.setWebViewClient(new WebViewClient()
    {
         //On enleve le progress quand la page est chargée
        public void onPageFinished(WebView view, String url)
              { 
                pd.dismiss();
                 super.onPageFinished(view, url);
              }

So i've tried several things to make this work.

public void onBackPressed (){

    if (webView.isFocused() && webView.canGoBack()) {
            webView.goBack(); 

    }
 super.onBackPressed(); 

works as expected, the webview goes back and when it can't anymore switch back to activity A and if you press again leaves the app

i'm actually using :

public void onBackPressed (){

    if (webView.isFocused() && webView.canGoBack()) {
            webView.goBack();       
    }

    else

    {

            AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.setMessage("Voulez vous quitter ?")
                   .setCancelable(false)
                   .setPositiveButton("Oui", new DialogInterface.OnClickListener() {
                       public void onClick(DialogInterface dialog, int id) {
                            finish();
                       }
                   })
                   .setNegativeButton("Non", new DialogInterface.OnClickListener() {
                       public void onClick(DialogInterface dialog, int id) {
                            dialog.cancel();
                       }
                   });
            AlertDialog alert = builder.create();
            alert.show();

    }
}

the prompts works fine, but it pops out when the webview can't go back anymore, if yes pressed you go back to activity A

how can i make this prompt pop when the current activity is A and not the webview? i don't really know how to do this, i've heard about fragments, is that the way to do it ?

hope this is clear.