public Builder setKey(java.lang.String value) {
          if (value == null) {
            throw new NullPointerException();
          }
          key_ = value;
          bitField0_ |= 0x00000004;
          onChanged();
          return this;
        }
<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>

@param value The key to set.
@return This builder for chaining.
java-visionai/proto-google-cloud-visionai-v1/src/main/java/com/google/cloud/visionai/v1/Application.java