@Override
  public String toString() {
    return String.format("StreamSpec: id=%s, systemName=%s, pName=%s, partCount=%d, config=%s.", id, systemName, physicalName, partitionCount, Joiner.on(",").withKeyValueSeparator("=").join(config));
  }
Copies this StreamSpec, but applies a new partitionCount.

This method is not static s.t. subclasses can override it.

@param partitionCount  The partitionCount for the returned StreamSpec.
@return                A copy of this StreamSpec with the specified partitionCount.
samza-api/src/main/java/org/apache/samza/system/StreamSpec.java