@Override public boolean equals(Object o) {
    if (o == this) return true;
    if (!(o instanceof Annotation)) return false;
    Annotation that = (Annotation) o;
    return timestamp == that.timestamp() && value.equals(that.value());
  }
Compares by {@link #timestamp}, then {@link #value}.
zipkin/src/main/java/zipkin2/Annotation.java