-BrowserFrame- how to set destination url

Hello, a simple question.
I created a BrowserFrame like this :


Browser sample = new BrowserFrame(“browser”, new ExternalResource(
http://example.com”));

and this frame go to example.com as first page. How i can set the url for second navigation?
I created a address bar and a button, but with “sample.setSource( url )” i am not able to change the url of BrowserFrame:


public void buttonClick(ClickEvent event) {
sample.setSource(editor.getTextField_addessBar().getValue()));

Thank you for help,
Gianluca