https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/SparkContext.scala
package org.apache.spark //定义spark包 import scala.language.implicitConversions //导入各类包。。。。
class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationClient { //定义类 SparkContext，传入配置参数SparkConf，继承特质Logging及ExecutorAllocationClient
def this() = this(new SparkConf()) //以下一系列辅助构造器，适应各种参数传入构造
def this(config: SparkConf, preferredNodeLocationData: Map[String, Set[SplitInfo]]) = { this(config) logWarning("Passing in preferred locations has no effect at all, see SPARK-8949") }
def this(master: String, appName: String, conf: SparkConf) = this(SparkContext.updatedConf(conf, master, appName))
def this( master: String, appName: String, sparkHome: String = null, jars: Seq[String] = Nil, environment: Map[String, String] = Map(), preferredNodeLocationData: Map[String, Set[SplitInfo]] = Map()) = { this(SparkContext.updatedConf(new SparkConf(), master, appName, sparkHome, jars, environment)) if (preferredNodeLocationData.nonEmpty) { logWarning("Passing in preferred locations has no effect at all, see SPARK-8949") } } // NOTE: The below constructors could be consolidated using default arguments. Due to // Scala bug SI-8479, however, this causes the compile step to fail when generating docs. // Until we have a good workaround for that bug the constructors remain broken out. /** * Alternative constructor that allows setting common Spark properties directly * * @param master Cluster URL to connect to (e.g. mesos://host:port, spark://host:port, local[4]). * @param appName A name for your application, to display on the cluster web UI. */ private[spark] def this(master: String, appName: String) = this(master, appName, null, Nil, Map()) /** * Alternative constructor that allows setting common Spark properties directly * * @param master Cluster URL to connect to (e.g. mesos://host:port, spark://host:port, local[4]). * @param appName A name for your application, to display on the cluster web UI. * @param sparkHome Location where Spark is installed on cluster nodes. */ private[spark] def this(master: String, appName: String, sparkHome: String) = this(master, appName, sparkHome, Nil, Map()) /** * Alternative constructor that allows setting common Spark properties directly * * @param master Cluster URL to connect to (e.g. mesos://host:port, spark://host:port, local[4]). * @param appName A name for your application, to display on the cluster web UI. * @param sparkHome Location where Spark is installed on cluster nodes. * @param jars Collection of JARs to send to the cluster. These can be paths on the local file * system or HDFS, HTTP, HTTPS, or FTP URLs. */ private[spark] def this(master: String, appName: String, sparkHome: String, jars: Seq[String]) = this(master, appName, sparkHome, jars, Map())
