java - 使用javapriorityQueue删除方法

Question

我正在寻找带有java的dijkstra算法。

下面的代码可以正常工作。

public static void computePaths(Vertex source, Subway p, int broken)
    {
        //set the source vertex distance to 0 (as distance source->source=0)
        source.minDistance=0;
        //init queue , add source to keep track of nodes visited (cloud)
        PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>();
        vertexQueue.add(source);

        //keep track of total vertices tracked so as not to go in circles
        List<Integer> l=new LinkedList<Integer>();

    // while the cloud is not empty
    while (!vertexQueue.isEmpty()) {
        // take the head as u and...
        Vertex u = vertexQueue.poll();
        //(add position of u to the tracking list)
        l.add(new Integer(u.pos));


            // ...Visit each edge exiting u
            Iterator<Edge> it=(p.subwayNetwork.getEdges(u.pos)).iterator();
            while (it.hasNext())
            {

                Edge e= it.next();
                Vertex v = e.dest;
                Double weight = e.weight;
                // calculate the distance from u to the node v
                Double distanceThroughU = u.minDistance + weight;

                // if the distance is less then the min. distance, and not already visited, and  neither
                // the vertice and edge are broken
                if (distanceThroughU < v.minDistance && !l.contains(v.pos) && v.pos!=broken && !e.broken) {
                    //remove the node form the queue and update the distance and prev. value
                    vertexQueue.remove(v);
                    //update the distance
                    v.minDistance=distanceThroughU;
                    //update the path visited till now 
                    v.previous = u;
                    //reenter the node with the new distance
                    vertexQueue.add(v);

                }
            }

        }
    }

为什么vertexQueue.remove(v);没有发生错误？

自从我们初始化队列以来，我们添加一些内容然后轮询。

所以队列可能是空的。

我认为删除操作会发生NoSuchElementException错误。

但运行正常。

如有建议，我们将不胜感激

Answer 1

remove() 方法的返回值是 bool。如果队列因调用而改变，则返回“true”，否则返回“false”，但也不异常(exception)!

来源:https://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html#remove(java.lang.Object)