图可以描绘大部分任何逻辑，给个我用图的实例

public void walk(IGraph graph, AbstractNodeVisitor<IPigBuilder> visitor, PigWriter writer)  throws NodeErrorException{
        this.graph = graph;
        setAllNodesUnvisited();

        Stack<AbstractNode> visitedNodes = new Stack<AbstractNode>();

        for (AbstractNode node: graph.getNodeList()){
            if (getVisitState(node) == VisitState.UNVISITED){
                dfs(node, visitedNodes);
            }
        }

        while (!visitedNodes.empty()){
            visitedNodes.pop().accept(visitor).write(writer);
        }
    }

    private void dfs(AbstractNode node, Stack<AbstractNode> visitedNodes){
        setVisitState(node, VisitState.PASSED);
        Set<AbstractNode> succNodes = GraphHelper.getSuccNodes(node);

        for (AbstractNode succNode: succNodes){
            VisitState state = getVisitState(succNode);
            if (state == VisitState.UNVISITED){
                dfs(succNode, visitedNodes);
            }
            else if(state == VisitState.PASSED){
                throw new IllegalStateException("Loop");
            }
        }
        setVisitState(node, VisitState.VISITED);
        visitedNodes.push(node);
    }