How to show pop-up message when exit android webview app

Question

I just made my first Android webview application.

It works fine but there's still one thing I'd like to add to the webview: an exit button.

How I like to do that:

When users click on the back button of the phone, they go back to the previous page that they visited. Now when they are back on the first page they visited and go back, the app automatically closes. There I would like to show a pop-up message that says "Are you sure you want to exit?"

How can I display a message like that?

My code:

// Open previous opened link from history on webview when back button pressed

@Override
// Detect when the back button is pressed
public void onBackPressed() {
    if(webView.canGoBack()) {
        webView.goBack();
    } else {
        // Let the system handle the back button
        super.onBackPressed();
    }
}

EDIT: I made some changes to my code. This is the result::

private Boolean exit = false;
@Override
// Detect when the back button is pressed
public void onBackPressed() {
    if(webView.canGoBack()) {
        webView.goBack();
    }
    else {
        if (exit)
            this.finish();
        else {
            Toast.makeText(this, "Press again to close.",
                Toast.LENGTH_SHORT).show();
                exit = true;
                new Handler().postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        exit = false;
                    }
                }, 3 * 1000);
        }    

    // Let the system handle the back button
    super.onBackPressed();
    }
}

Answer 1

Adding a toast in the "else" clause is the correct answer.

Make sure to remove "super.onbackpressed". If you don't do that, you're not giving the user any chance of deciding whether he wants to exit or not. The pop-up message will just show up and the app will be closed at the same time.