重写方法需要 override 
只有主构造函数才能往父类构造函数传参数


// 主构造函数参数 加 val var 才能作为类字段  外部可访问
class Vehicle(val id: Int, val year: Int) {
  override def toString(): String = "ID:" + id + " Year:" + year
}

// id year 参数  override
class Cars(override val id: Int, override val year: Int, var fuelLevel: Int) extends Vehicle(id, year) {
  // 重写 toString 加 override
  override def toString(): String = super.toString() + " Fuel Level:" + fuelLevel
}

object Cars {
  def main(args: Array[String]) {
    val car = new Cars(1, 2022, 99)
    println(car)
  }
}