@Override public int hashCode() {
    int h = 1;
    h *= 1000003;
    h ^= (int) ((timestamp >>> 32) ^ timestamp);
    h *= 1000003;
    h ^= value.hashCode();
    return h;
  }
Compares by {@link #timestamp}, then {@link #value}.
zipkin/src/main/java/zipkin2/Annotation.java