Kotlin 单例

饿汉式：

object SingletonDemo

双检锁：
class SingletonDemo private constructor() {
    companion object {
        val instance: SingletonDemo by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) {
        SingletonDemo() }
    }
}


静态内部类：
class SingletonDemo private constructor() {
    companion object {
        val instance = SingletonHolder.holder
    }

    private object SingletonHolder {
        val holder= SingletonDemo()
    }

}


安全的双检锁：
class SingletonDemo private constructor(private val property: Int) {//这里可以根据实际需求发生改变
  
    companion object {
        @Volatile private var instance: SingletonDemo? = null
        fun getInstance(property: Int) =
                instance ?: synchronized(this) {
                    instance ?: SingletonDemo(property).also { instance = it }
                }
    }
}