scalaclass和object的区别

Scala中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)

1. private[spark] class Client(
   
2.     val args: ClientArguments,
   
3.     val hadoopConf: Configuration,
   
4.     val sparkConf: SparkConf)
   
5.   extends Logging {...}
   
6. 
   
7. object Client extends Logging {
   
8.   def main(argStrings: Array[String]) {
   
9.     if (!sys.props.contains("SPARK_SUBMIT")) {
   
10.       logWarning("WARNING: This client is deprecated and will be removed in a " +
    
11.         "future version of Spark. Use ./bin/spark-submit with \"--master yarn\"")
    
12.     }
    
13. 
    
14.     // Set an env variable indicating we are running in YARN mode.
    
15.     // Note that any env variable with the SPARK_ prefix gets propagated to all (remote) processes
    
16.     System.setProperty("SPARK_YARN_MODE", "true")
    
17.     val sparkConf = new SparkConf
    
18. 
    
19.     val args = new ClientArguments(argStrings, sparkConf)
    
20.     // to maintain backwards-compatibility
    
21.     if (!Utils.isDynamicAllocationEnabled(sparkConf)) {
    
22.       sparkConf.setIfMissing("spark.executor.instances", args.numExecutors.toString)
    
23.     }
    
24.     new Client(args, sparkConf).run()
    
25.   }
    
26.  ......
    
27. }