<a id="myid" href="something?a=b">Link</a>

<a id="myid" href="something?a=b" onclick="goSomewhereElse(); return false;">Link</a>

<a id="myid" href="javascript:;">Link</a>

<g:Anchor ui:field="myLink1">The Link To Click</g:Anchor>

@UiField
protected Anchor myLink1;

@UiHandler("myLink1")
public void handleMyLink1Click(ClickEvent event)
{
    //code to execute on click;
    event.preventDefault(); //If you want the href present
}