累加器：只允许add操作，常用于实现计数。 ```scala object App { def main(args: Array[String]): Unit = { val spark:SparkSession = SparkSession.builder() .master("local[4]") .appName(this.getClass.getName) .getOrCreate() val sc:SparkContext = spark.sparkContext import spark.implicits._ val accum = sc.longAccumulator("My Accumulator") // 获取累加器 sc.parallelize(Array(1, 2, 3, 4)).foreach(x => accum.add(x)) println(accum.value) // 10 println(accum.count) // 4 } } ```