title: How add @UiHandler click of gwt button?
body: <p>I am gwt2.3 with uibinder.In My application I am made a button and want to add a click handler
  bu using @UiHandler annotaion.Below is my code: ui.xml</p>
  
  <pre><code>&lt;g:HTMLPanel&gt;
      &lt;g:VerticalPanel&gt;
          &lt;g:HorizontalPanel &gt;
          &lt;g:Button ui:field="btnAccessLevel" text="Access Level" styleName="submit" /&gt;
          &lt;g:Button ui:field="btnSave" text="Save" styleName= "submit" /&gt;
          &lt;/g:HorizontalPanel&gt;
          &lt;g:AbsolutePanel ui:field="formPanel"&gt;
          &lt;/g:AbsolutePanel&gt;
          &lt;g:AbsolutePanel ui:field="accessLevelPanel"&gt;
          &lt;/g:AbsolutePanel&gt;
      &lt;/g:VerticalPanel&gt;
  &lt;/g:HTMLPanel&gt;
  </code></pre>
  
  <p>.java</p>
  
  <pre><code>    @UiField
  Button btnAccessLevel;
  
  
  @Inject
  public DocumentFormView(final Binder binder) {
      widget = binder.createAndBindUi(this);
       @UiHandler("btnAccessLevel")
       void handleClick(ClickEvent e) {
          Window.alert("Hello, AJAX");
        }
  }
  </code></pre>
  
  <p>When I am trying this I am getting this error:
  <strong>void is an invalid type for the variable handleClick</strong> 
  I am not getting what issue is.Please help me out.
  Thanks in advance.</p>