@Override
  public String toString() {
    StringBuilder builder = new StringBuilder();
    builder.append("ActivityImpl(name=").append(name).append(", start=");
    nanoToString(start, builder);
    builder.append(", end=");
    nanoToString(end, builder);
    builder.append(", category=").append(category).append(")");
    return builder.toString();
  }
@Override
  public String toString()