@java.lang.Override
        public long getId() {
          return id_;
        }
<pre>
An identifier for the MessageEvent's message that can be used to match
`SENT` and `RECEIVED` MessageEvents.
</pre>

<code>int64 id = 2;</code>

@return The id.
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/Span.java