GWT OpenLayers set sum of values of underlying VectorFeatures on cluster point

I'm using gwt-openlayers-1.0, currently learning this example (Animated Cluster Strategy).

In my project each VectoreFeature has a numeric label and I want to display sums of label values of underlying points on each cluster point. Is there a way to do that?

upd:
According to this article (The “Most Important” Strategy part) in JS it would look like this:

// for each feature:
feature.attributes = { result_count: 10 };
...
var style = new OpenLayers.Style({
  ...
  } , context: {
    label: function(feature) {
      if (feature.cluster) {
        var result_count = 0;
        for (var i = 0; i < feature.cluster.length; i++) {
          result_count += feature.cluster[i].attributes.result_count;
        }
        features.attributes.label = result_count.toString();
      } else {
        features.attributes.label = features.attributes.result_count.toString();
      }
    }
  }

But I can't find a way to implement this in gwt-openlayers:

org.gwtopenmaps.openlayers.client.Style style = new org.gwtopenmaps.openlayers.client.Style();
style.setLabel( ??? );

Solution

In method where I assign strategy to the VectorLayer:

{
    org.gwtopenmaps.openlayers.client.Style style = new org.gwtopenmaps.openlayers.client.Style();
    style.setJSObject(getOpenLayersStyle());
}

And where the magic is done:

private native JSObject getOpenLayersStyle() /*-{
    var style = new $wnd.OpenLayers.Style({
        fontColor: "#FFFFFF",
        fontSize: "12px",
        label: "${countLabel}"
        }, { context: {
            countLabel: function(feature) {
                var countLabel;
                if (feature.cluster) {
                    var result_count = 0;
                    for (var i = 0; i < feature.cluster.length; i++) {
                        result_count += feature.cluster[i].attributes.result_count;
                    }
                    countLabel = result_count.toString();
                } else {
                    countLabel = feature.attributes.result_count.toString();
                }
                feature.attributes.label = countLabel;
                return countLabel;
            }
        }
    });
    return style;
}-*/;