@Override
  public String toString() {
    if (keyBucket != -1) {
      return "SystemStreamPartition [" + system + ", " + stream + ", " + partition.getPartitionId() + ", " + keyBucket + "]";
    }
    return "SystemStreamPartition [" + system + ", " + stream + ", " + partition.getPartitionId() + "]";
  }
Constructs a Samza stream partition object based upon another Samza stream and a specified partition.
@param other Reference to an already existing Samza stream.
@param partition Reference to an already existing Samza partition.
samza-api/src/main/java/org/apache/samza/system/SystemStreamPartition.java