@java.lang.Override
  public int hashCode() {
    if (memoizedHashCode != 0) {
      return memoizedHashCode;
    }
    int hash = 41;
    hash = (19 * hash) + getDescriptor().hashCode();
    if (hasStackFrames()) {
      hash = (37 * hash) + STACK_FRAMES_FIELD_NUMBER;
      hash = (53 * hash) + getStackFrames().hashCode();
    }
    hash = (37 * hash) + STACK_TRACE_HASH_ID_FIELD_NUMBER;
    hash = (53 * hash) + com.google.protobuf.Internal.hashLong(getStackTraceHashId());
    hash = (29 * hash) + getUnknownFields().hashCode();
    memoizedHashCode = hash;
    return hash;
  }
<pre>
The hash ID is used to conserve network bandwidth for duplicate
stack traces within a single trace.

Often multiple spans will have identical stack traces.
The first occurrence of a stack trace should contain both the
`stackFrame` content and a value in `stackTraceHashId`.

Subsequent spans within the same request can refer
to that stack trace by only setting `stackTraceHashId`.
</pre>

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

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