android：kotlin语言中使用单例模式

• 不带参数

class StudentDaoOpe private constructor() {

    private object mHolder {
        val instance = StudentDaoOpe()
    }

    companion object {
        fun getInstance(): StudentDaoOpe {
            return mHolder.instance
        }
    }
}

• 带参数

class DbManager private constructor(mContext: Context) {


    companion object {
        @Volatile
        var instance: DbManager? = null

        fun getInstance(mContext: Context): DbManager? {
            if (instance == null) {
                synchronized(DbManager::class) {
                    if (instance == null) {
                        instance = DbManager(mContext)
                    }
                }
            }
            return instance
        }
    }
}