public String getPhysicalName(String streamId) {
    // use streamId as the default physical name
    return getOrDefault(String.format(PHYSICAL_NAME_FOR_STREAM_ID, streamId), streamId);
  }
Gets the physical name for the specified streamId.

@param streamId the identifier for the stream in the config.
@return the physical identifier for the stream or the default if it is undefined.
samza-core/src/main/java/org/apache/samza/config/StreamConfig.java