@java.lang.Override
  public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(name_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 1, name_);
    }
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(sourceText_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 2, sourceText_);
    }
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(targetText_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 3, targetText_);
    }
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(usage_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 4, usage_);
    }
    getUnknownFields().writeTo(output);
  }
<pre>
Output only. Usage of the sentence pair. Options are TRAIN|VALIDATION|TEST.
</pre>

<code>string usage = 4 [(.google.api.field_behavior) = OUTPUT_ONLY];</code>

@return The bytes for usage.
java-translate/proto-google-cloud-translate-v3/src/main/java/com/google/cloud/translate/v3/Example.java