@Override
 public int hashCode() {
   final int prime = 31;
   int result = 1;
   result = prime * result + ((axes == null) ? 0 : axes.hashCode());
   result = prime * result + ((data == null) ? 0 : data.hashCode());
   result = prime * result + ((file == null) ? 0 : file.hashCode());
   result = prime * result + ((monitor == null) ? 0 : monitor.hashCode());
   result = prime * result + ((parent == null) ? 0 : parent.hashCode());
   result = prime * result + ((userData == null) ? 0 : userData.hashCode());
   return result;
 }