code: public void setOpacity(double opacity) {
  		getLayerInfo().setStyle(Double.toString(opacity));
  		renderer.setOpacity(opacity);
  	}
docs: Apply a new opacity on the entire raster layer. Changing the opacity on a layer does NOT fire a layer style
  changed event.
  
  @param opacity The new opacity value. Must be a value between 0 and 1, where 0 means invisible and 1 is totally
  visible.