This method shows how to add a event listener to a div element in GWT

Adding Events to Div in GWT

private NodeList<Element> pageDIVElements;
  public void initDiv() {
    MyDIVEventHandler handler = new MyDIVEventHandler();
    pageDIVElements = Document.get().getElementsByTagName("div");
    for (int i = 0; i < pageDIVElements.getLength(); i++) {
      Element elem = pageDIVElements.getItem(i);
      elem.addClassName("etvoila");
      com.google.gwt.user.client.Element castedElem = (com.google.gwt.user.client.Element) elem;
      DOM.setEventListener(castedElem, handler);
    }

class MyDIVEventHandler implements EventListener {
  private Element divElement;
  @Override
  public void onBrowserEvent(Event event) {

    Window.alert("Yeepee");
    if (event.equals(Event.ONMOUSEOVER)) {
      Window.alert("ONMOUSEOVER");
      divElement = Element.as(((NativeEvent) event).getEventTarget());
      divElement.setPropertyString("background-color", "#C6D4E6");
    } else if (event.equals(Event.ONMOUSEOUT)) {
      divElement = Element.as(((NativeEvent) event).getEventTarget());
      divElement.setAttribute("background-color", "");
    }else if (event.equals(Event.ONCLICK)) {
      divElement = Element.as(((NativeEvent) event).getEventTarget());
      divElement.setAttribute("background-color", "");
      Window.alert("ONCLICK");
    }
  }
}