Question

scala class 和 object的区别

Answer 1

Scala中class类对象中不可有静态变量和静态方法，但是提供了“伴侣对象”的功能：在和类的同一个文件中定义同名的Object对象：(须在同一文件中；main方法定义在Object对象中)

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()
}
......
}