@java.lang.Override
      protected Builder newBuilderForType(
          com.google.protobuf.GeneratedMessageV3.BuilderParent parent) {
        Builder builder = new Builder(parent);
        return builder;
      }
<pre>
The key of the output resource, it has to be unique within the same
producer node. One producer node can output several output resources,
the key can be used to match corresponding output resources.
</pre>

<code>string key = 3;</code>

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