code: public PrepareContractionHierarchies useFixedNodeOrdering(NodeOrderingProvider nodeOrderingProvider) {
          if (nodeOrderingProvider.getNumNodes() != prepareGraph.getNodes()) {
              throw new IllegalArgumentException(
                      "contraction order size (" + nodeOrderingProvider.getNumNodes() + ")" +
                              " must be equal to number of nodes in graph (" + prepareGraph.getNodes() + ").");
          }
          this.nodeOrderingProvider = nodeOrderingProvider;
          return this;
      }
docs: Instead of heuristically determining a node ordering for the graph contraction it is also possible
  to use a fixed ordering. For example this allows re-using a previously calculated node ordering.
  This will speed up CH preparation, but might lead to slower queries.