@java.lang.Override
  public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(parent_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 1, parent_);
    }
    if (((bitField0_ & 0x00000001) != 0)) {
      output.writeMessage(2, getAnnotation());
    }
    if (((bitField0_ & 0x00000002) != 0)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 3, annotationId_);
    }
    getUnknownFields().writeTo(output);
  }
<pre>
Optional. The ID to use for the annotation, which will become the final
component of the annotation's resource name if user choose to specify.
Otherwise, annotation id will be generated by system.

This value should be up to 63 characters, and valid characters
are /[a-z][0-9]-/. The first character must be a letter, the last could be
a letter or a number.
</pre>

<code>optional string annotation_id = 3 [(.google.api.field_behavior) = OPTIONAL];</code>

@return The bytes for annotationId.
java-visionai/proto-google-cloud-visionai-v1/src/main/java/com/google/cloud/visionai/v1/CreateAnnotationRequest.java