public Builder addParts(int index, com.google.cloud.vertexai.api.Part.Builder builderForValue) {
      if (partsBuilder_ == null) {
        ensurePartsIsMutable();
        parts_.add(index, builderForValue.build());
        onChanged();
      } else {
        partsBuilder_.addMessage(index, builderForValue.build());
      }
      return this;
    }
<pre>
Required. Ordered `Parts` that constitute a single message. Parts may have
different IANA MIME types.
</pre>

<code>
repeated .google.cloud.vertexai.v1.Part parts = 2 [(.google.api.field_behavior) = REQUIRED];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/Content.java