ArcObjects: How to get a reference to layer in a java add in

Question

I am trying to implement a java add-in version of this solution: unique value symbolize layers from a lookup table. At the same time I want to start coding in Java for the ArcGIS Desktop, so I am rewriting the sample Custom renderer, which is implemented as a property page in the layers -> properties -> Symbology -> Custom Renderer tab. The above solution uses

IGeoFeatureLayer gfLayer = mxDoc.FocusMap.get_Layer(0) as IGeoFeatureLayer;    gfLayer.Renderer = (IFeatureRenderer)UvrItem.MakeUVR(@"Filepath");

Now, ArcMap surely knows the featurelayer, when editing its properties. But the Custom renderer is just handed a featureCursor. So I try to get a reference to GeoFeatureLayer through the activeView like this:

    public boolean canRender(IFeatureClass fc, IDisplay display) throws IOException, AutomationException {

    try {
        HookHelper hookhelper = new HookHelper();
        IActiveView activeView = hookhelper.getActiveView();
        System.out.println("The Layer Name Is:   " + activeView.getFocusMap().getLayer(0).getName());   
    } catch (Exception e) {
        System.out.println(e.getMessage() + e.getStackTrace().toString());
    }
    if (fc.getShapeType() == esriGeometryType.esriGeometryPolygon)
        return true;
    else
        return false;
}

But I get Error Message: Null.

If anyone more experienced than me knows the best way to do this in java, I would very much appreciate some advice.

Best Regards, Marianne B. Wiese