private Element htmlElement;
//the model contains all the information of the window
private E model;
//unique ID for each window
private String randomId = ""+Random.nextInt();

public MyClass(E model) {
    this.model = model;
    htmlElement = DOM.createInputText();
    htmlElement.setAttribute("value", model.getName());
    htmlElement.setId(randomId)
    setupTitleOnChange(htmlElement);
}

public final Canvas createWindow() {
    Window window = new Window();
    window.setTitle(htmlElement.getString())
    ...
}

//This method save the Title of the window and has to be called in the native method
private void OnChangeTitle(String randomId) {
    eventBus.fireEvent(new WindowNameChangeEvent(model, DOM.getElementById(randomId).getAttribute("value")));
}

public native void setupTitleOnChange(Element element) /*-{
    // TODO implement JSNI method to change the title of the window
}-*/;