object关键字，常用来作为kotlin中的单例模式
定义:
1.只有一个实例的类
2.不能自定义构造方法
3.可以实现接口，继承父类
4.反编译出来的class文件,就是java中static代码块中new对象的单例模式
class Driver10
interface OnExternalDriverMountListener{
fun onMount(driver: Driver10)
fun onUnmount(driver: Driver10)
}
abstract class Player
object MusicPlayer: Player(), OnExternalDriverMountListener{
override fun onMount(driver: Driver10) {}
override fun onUnmount(driver: Driver10) {}
val state : Int = 0
fun play(url : String){}
fun stop(){}
}
fun main(args: Array<String>) {
MusicPlayer.play("")
println(MusicPlayer.state)
}
