classMediaPlayerHelpprivateconstructor(context:Context){
val mContext=context
init {
val mMediaPlayer=MediaPlayer()}//构造器执行的构造函数
companion object{@Volatileprivatevar instance:MediaPlayerHelp?=null
fun getInstance(context:Context){
instance?:synchronized(this){
instance?:MediaPlayerHelp(context).also { instance=it }}}}}
无参的DCL
classSingletonDemoprivateconstructor(){
companion object {
val instance:SingletonDemo by lazy(mode =LazyThreadSafetyMode.SYNCHRONIZED){SingletonDemo()}}}