scala默认参数值是什么

 /**   * Return a sampled subset of this RDD.   *   * @param withReplacement can elements be sampled multiple times (replaced when sampled out)   * @param fraction expected size of the sample as a fraction of this RDD's size   *  without replacement: probability that each element is chosen; fraction must be [0, 1]   *  with replacement: expected number of times each element is chosen; fraction must be greater   *  than or equal to 0   * @param seed seed for the random number generator   *   * @note This is NOT guaranteed to provide exactly the fraction of the count   * of the given [[RDD]].   */  def sample(      withReplacement: Boolean,      fraction: Double,      seed: Long = Utils.random.nextLong): RDD[T] = {    require(fraction >= 0,      s"Fraction must be nonnegative, but got ${fraction}")
    withScope {      require(fraction >= 0.0, "Negative fraction value: " + fraction)      if (withReplacement) {        new PartitionwiseSampledRDD[T, T](this, new PoissonSampler[T](fraction), true, seed)      } else {        new PartitionwiseSampledRDD[T, T](this, new BernoulliSampler[T](fraction), true, seed)      }    }  }

def log(message: String, level: String = "INFO") = println(s"$level: $message")
log("System starting")  log("User not found", "WARNING")  

class Point(val x: Double = 0, val y: Double = 0)
val point1 = new Point(y = 1)

class Point(val x: Double = 0, val y: Double = 0)

public class Main {    public static void main(String[] args) {        Point point = new Point(1);      }}