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()
　　}
　　......
　　}