Added Java API for countApproxDistinct

core/src/main/scala/org/apache/spark/api/java/JavaRDDLike.scala

@@ -444,4 +444,15 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
     val comp = com.google.common.collect.Ordering.natural().asInstanceOf[Comparator[T]]
     takeOrdered(num, comp)
   }
+
+  /**
+   * Return approximate number of distinct elements in the RDD.
+   *
+   * The accuracy of approximation can be controlled through the relative standard deviation
+   * (relativeSD) parameter, which also controls the amount of memory used. Lower values result in
+   * more accurate counts but increase the memory footprint and vise versa. The default value of
+   * relativeSD is 0.05.
+   */
+  def countApproxDistinct(relativeSD: Double = 0.05): Long = rdd.countApproxDistinct(relativeSD)
+
 }