Question

我使用PriorityQueue实现了Dijkstra的算法。但是在运行代码时，我得到以下异常：

Exception in thread "main" java.lang.ClassCastException: Dijkstra$Vertex cannot be cast to java.lang.Comparable
    at java.util.PriorityQueue.siftUpComparable(Unknown Source)
    at java.util.PriorityQueue.siftUp(Unknown Source)
    at java.util.PriorityQueue.offer(Unknown Source)
    at java.util.PriorityQueue.add(Unknown Source)
    at Dijkstra.dijkstra(Dijkstra.java:55)
    at Dijkstra.main(Dijkstra.java:89)

使用的代码是：

import java.util.HashSet;
import java.util.PriorityQueue;


public class Dijkstra {
    static class Vertex{
        private int vertexid;
        private Double distance;

        public Vertex(int vertexid, Double distance) {
            this.vertexid = vertexid;
            this.distance = distance;
        }

        public int getVertexid() {
            return vertexid;
        }

        public Double getDistance() {
            return distance;
        }

        public int compareTo(Vertex other) {
            return this.getDistance().compareTo(other.getDistance());
        }

        public boolean equals(Object o) {
            if (o instanceof Vertex) {
                Vertex v = (Vertex) o;
                return vertexid == v.vertexid && distance == v.distance;
            }
            return false;
        }
    }

    public static void dijkstra(double g[][], int n, int m, int source) {
        // g is the adjacency matrix
        // n is the number of nodes
        // m is the number of edges

        // initialize shortest path

        double d[] = new double[n];

        d[source] = 0;
        for (int i = 0; i < n; i++) {
            d[i] = Double.POSITIVE_INFINITY;
        }

        HashSet<Integer> s = new HashSet<Integer>();
        PriorityQueue<Vertex> q = new PriorityQueue<Vertex>();

        // initialize q
        for (int i = 0; i < n; i++) {
            q.add(new Vertex(i, d[i]));
        }

        Vertex u;

        while (!q.isEmpty()) {
            u = q.remove();
            System.out.println(u.getVertexid() + "\t" + u.getDistance());
            s.add(u.getVertexid());

            for (int i = 0; i < n; i++) {
                if (i != u.getVertexid() && g[u.getVertexid()][i] != Double.POSITIVE_INFINITY) {
                    if (u.getDistance().doubleValue() + g[u.getVertexid()][i] < d[i]) {
                        q.remove(new Vertex(i, d[i]));
                        d[i] = u.getDistance().doubleValue() + g[u.getVertexid()][i];
                        q.add(new Vertex(i, d[i]));
                    }
                }
            }
        }
    }

    public static void main(String[] args) {
        double graph[][] = {{0, 4, 0, 0, 0, 0, 0, 8, 0},
                {4, 0, 8, 0, 0, 0, 0, 11, 0},
                {0, 8, 0, 7, 0, 4, 0, 0, 2},
                {0, 0, 7, 0, 9, 14, 0, 0, 0},
                {0, 0, 0, 9, 0, 10, 0, 0, 0},
                {0, 0, 4, 14, 10, 0, 2, 0, 0},
                {0, 0, 0, 0, 0, 2, 0, 1, 6},
                {8, 11, 0, 0, 0, 0, 1, 0, 7},
                {0, 0, 2, 0, 0, 0, 6, 7, 0}
               };

        Dijkstra.dijkstra(graph, 8, 14, 0);
    }
}

Vertex类用于创建基本上存储顶点及其标签距离的结构。优先级队列将对此类的对象起作用，并将使用距离值作为删除操作的排序值。如何纠正异常？

Answer 1

请改为尝试：

static class Vertex implements Comparable<Vertex> {

尝试实现Dijkstra算法时无法转换为java.lang.Comparable异常

1 个答案: