private com.google.protobuf.SingleFieldBuilderV3<
            com.google.type.Date, com.google.type.Date.Builder, com.google.type.DateOrBuilder>
        getPublicationDateFieldBuilder() {
      if (publicationDateBuilder_ == null) {
        publicationDateBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.type.Date, com.google.type.Date.Builder, com.google.type.DateOrBuilder>(
                getPublicationDate(), getParentForChildren(), isClean());
        publicationDate_ = null;
      }
      return publicationDateBuilder_;
    }
<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