@java.lang.Override
  public int hashCode() {
    if (memoizedHashCode != 0) {
      return memoizedHashCode;
    }
    int hash = 41;
    hash = (19 * hash) + getDescriptor().hashCode();
    hash = (37 * hash) + START_INDEX_FIELD_NUMBER;
    hash = (53 * hash) + getStartIndex();
    hash = (37 * hash) + END_INDEX_FIELD_NUMBER;
    hash = (53 * hash) + getEndIndex();
    hash = (37 * hash) + URI_FIELD_NUMBER;
    hash = (53 * hash) + getUri().hashCode();
    hash = (37 * hash) + TITLE_FIELD_NUMBER;
    hash = (53 * hash) + getTitle().hashCode();
    hash = (37 * hash) + LICENSE_FIELD_NUMBER;
    hash = (53 * hash) + getLicense().hashCode();
    if (hasPublicationDate()) {
      hash = (37 * hash) + PUBLICATION_DATE_FIELD_NUMBER;
      hash = (53 * hash) + getPublicationDate().hashCode();
    }
    hash = (29 * hash) + getUnknownFields().hashCode();
    memoizedHashCode = hash;
    return hash;
  }
<pre>
Output only. Publication date of the attribution.
</pre>

<code>.google.type.Date publication_date = 6 [(.google.api.field_behavior) = OUTPUT_ONLY];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/Citation.java