HoverExample.scala

class HoverComponent extends Component {
  // "Leaked" implementation detail of our `HoverSystem`
  var time: Float
}

class PositionComponent extends Component {
  var x: Float
  var y: Float
}

class Coin extends Entity {
  add(new PositionComponent())
  add(new HoverComponent())
}

class HoverSystem extends EntitySystem {

  /** Allow only entities which required components */
  require(classOf[HoverComponent], classOf[PositionComponent])

  /** Called each frame with the `entity` to be processed and the
      `elapsed` time since the last frame was rendered */
  override def process(entity: Entity, elapsed: Float): Unit = {
    val position = entity.get[PositionComponent]
    val hover = entity.get[HoverComponent]

    position.y += 10 * sin(hover.time)
    hover.time += elapsed
  }
}