public SubClass withPhysicalName(String physicalName) {
    this.physicalNameOptional = Optional.ofNullable(physicalName);
    return (SubClass) this;
  }
The physical name of the stream on the system on which this stream will be accessed.
This is opposed to the {@code streamId} which is the logical name that Samza uses to identify the stream.
<p>
A physical name could be a Kafka topic name, an HDFS file URN, or any other system-specific identifier.
<p>
If not provided, the logical {@code streamId} is used as the physical name.

@param physicalName physical name for this stream.
@return this stream descriptor.
samza-api/src/main/java/org/apache/samza/system/descriptors/StreamDescriptor.java