Scala 访问权限控制——Scala Access Modifiers

其他的都和Java的差不多，唯一的区别是多了Scope protect

Scope of protection

Access modifiers in Scala can be augmented with qualifiers. A modifier of the form private[X] or protected[X] means that access is private or protected "up to" X, where X designates some enclosing package, class or singleton
object. Consider the following example:

package society {
   package professional {
      class Executive {
         private[professional] var workDetails = null
         private[society] var friends = null
         private[this] var secrets = null

         def help(another : Executive) {
            println(another.workDetails)
            println(another.secrets) //ERROR
         }
      }
   }
}

Note the following points from the above example:

Variable workDetails will be accessible to any class within the enclosing packageprofessional.

Variable friends will be accessible to any class within the enclosing packagesociety.

Variable secrets will be accessible only on the implicit object within instance methods (this).

Spark中到处都可以看到 Scope of protection, 例如以下代码段

// Create the Spark execution environment (cache, map output tracker, etc)
  private[spark] val env = SparkEnv.create(
    conf,
    "<driver>",
    conf.get("spark.driver.host"),
    conf.get("spark.driver.port").toInt,
    isDriver = true,
    isLocal = isLocal)
  SparkEnv.set(env)

  // Used to store a URL for each static file/jar together with the file's local timestamp
  private[spark] val addedFiles = HashMap[String, Long]()
  private[spark] val addedJars = HashMap[String, Long]()

  // Keeps track of all persisted RDDs
  private[spark] val persistentRdds = new TimeStampedHashMap[Int, RDD[_]]
  private[spark] val metadataCleaner =
    new MetadataCleaner(MetadataCleanerType.SPARK_CONTEXT, this.cleanup, conf)

  // Initialize the Spark UI
  private[spark] val ui = new SparkUI(this)