code: public double getBondLengthValue(String id1, String id2) {
          String dkey = "";
          if (pSet.containsKey(("bond" + id1 + ";" + id2))) {
              dkey = "bond" + id1 + ";" + id2;
          } else if (pSet.containsKey(("bond" + id2 + ";" + id1))) {
              dkey = "bond" + id2 + ";" + id1;
          } else {
              logger.warn("KEYError: Unknown distance key in pSet: " + id2 + ";" + id1
                                 + " take default bond length: " + DEFAULT_BOND_LENGTH);
              return DEFAULT_BOND_LENGTH;
          }
          return ((Double) (pSet.get(dkey).get(0))).doubleValue();
      }
docs: Gets the distanceValue attribute of the parameter set.
  
  @param  id1            atom1 id
  @param  id2            atom2 id
  @return                The distanceValue value from the force field parameter set