Scala中類物件中不可有靜態變數和靜態方法，但是提供了“伴侶物件”的功能：在和類的同一個檔案中定義同名的Object物件：(須在同一檔案中；main方法定義在Object物件中)

private[spark] class Client(
val args: ClientArguments,
val hadoopConf: Configuration,
val sparkConf: SparkConf)
extends Logging {...}
object Client extends Logging {
def main(argStrings: Array[String]) {
if (!sys.props.contains("SPARK_SUBMIT")) {
logWarning("WARNING: This client is deprecated and will be removed in a " +
"future version of Spark. Use ./bin/spark-submit with \"--master yarn\"")
}
// Set an env variable indicating we are running in YARN mode.
// Note that any env variable with the SPARK_ prefix gets propagated to all (remote) processes
System.setProperty("SPARK_YARN_MODE", "true")
val sparkConf = new SparkConf
val args = new ClientArguments(argStrings, sparkConf)
// to maintain backwards-compatibility
if (!Utils.isDynamicAllocationEnabled(sparkConf)) {
sparkConf.setIfMissing("spark.executor.instances", args.numExecutors.toString)
}
new Client(args, sparkConf).run()
}
......
}

scala class和object的區別

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