How to catch mouse over a Feature

[NARTech001]

Hello,
I want to capture the mouse movements over my Features...but it does not work with the following code (which seems to be correct for me!). Have I missed something ?

map.on("pointermove", evt-> {
Pixel pixel = map.getEventPixel(evt.getCurrentTarget());
map.forEachFeatureAtPixel(pixel, new ol.FeatureAtPixelFunction() {
@OverRide
public boolean call(Feature feature, ol.layer.Layer layer) {
// Found a feature under the pointer
Window.alert("Hovered over feature: " + feature.getId());
return false;
}
});
});