code: public List<AtomContact> getContactsWithinDistance(double distance) {
  
  		if (distance>=cutoff)
  			throw new IllegalArgumentException("Given distance "+
  					String.format("%.2f", distance)+" is larger than contacts' distance cutoff "+
  					String.format("%.2f", cutoff));
  
  		List<AtomContact> list = new ArrayList<AtomContact>();
  		for (AtomContact contact:this.contacts.values()) {
  			if (contact.getDistance()<distance) {
  				list.add(contact);
  			}
  		}
  		return list;
  	}
docs: Returns the list of contacts from this set that are within the given distance.
  @param distance
  @return
  @throws IllegalArgumentException if given distance is larger than distance cutoff
  used for calculation of contacts