ReverseDependencyOrderWalker traverses the graph in such a way that no node is visited
before all the nodes that are its successors on have been visited. Beyond this, it does not
guarantee any particular order. So, you have a graph with node 1 2 3 4, and
edges 1->3, 2->3, and 3->4, this walker guarantees that 4 will be visited
before 3 and 3 before 1 and 2, but it does not guarantee whether 1 or 2 will be
Fields inherited from class org.apache.pig.impl.plan.PlanWalker
Return a new instance of this same type of walker for a subplan.
When this method is called the same type of walker with the
provided plan set as the plan, must be returned. This can then be
used to walk subplans. This allows abstract visitors to clone
walkers without knowning the type of walker their subclasses used.