private com.google.protobuf.SingleFieldBuilderV3<
              com.google.cloud.translate.v3.GcsInputSource,
              com.google.cloud.translate.v3.GcsInputSource.Builder,
              com.google.cloud.translate.v3.GcsInputSourceOrBuilder>
          getGcsSourceFieldBuilder() {
        if (gcsSourceBuilder_ == null) {
          if (!(sourceCase_ == 3)) {
            source_ = com.google.cloud.translate.v3.GcsInputSource.getDefaultInstance();
          }
          gcsSourceBuilder_ =
              new com.google.protobuf.SingleFieldBuilderV3<
                  com.google.cloud.translate.v3.GcsInputSource,
                  com.google.cloud.translate.v3.GcsInputSource.Builder,
                  com.google.cloud.translate.v3.GcsInputSourceOrBuilder>(
                  (com.google.cloud.translate.v3.GcsInputSource) source_,
                  getParentForChildren(),
                  isClean());
          source_ = null;
        }
        sourceCase_ = 3;
        onChanged();
        return gcsSourceBuilder_;
      }
<pre>
Google Cloud Storage file source.
</pre>

<code>.google.cloud.translation.v3.GcsInputSource gcs_source = 3;</code>
java-translate/proto-google-cloud-translate-v3/src/main/java/com/google/cloud/translate/v3/DatasetInputConfig.java