無法找到我得到此NullPointException的原因。它指向2條特定線路。NullPointerException找不到該錯誤
這是錯誤:
Exception in thread "main" java.lang.NullPointerException
at Railroad.dijkstra(Railroad.java:52)
at Railroad.main(Railroad.java:36)
這些是2行:
dijkstra(A);
for (Edge x : w.edges){
這是爲了方便起見整個代碼:
過帳整個代碼爲更容易理解,其中我來自。希望它會有所幫助,謝謝!
Vertex[] vertices = { A, B, C, D, E, F, G, H, I, J, K, L, M };
dijkstra(A);
for (Vertex v : vertices)
{
System.out.println("Distance to " + v + ": " + v.shortestDist);
List<Vertex> trip = cheapestTrip(v);
System.out.println("Path: " + trip);
}
}
public static void dijkstra(Vertex s){
s.shortestDist = 0;
PriorityQueue<Vertex> cityQueue = new PriorityQueue<Vertex>();
cityQueue.add(s);
while(!cityQueue.isEmpty()){
Vertex w = cityQueue.poll();
for (Edge x : w.edges){
Vertex v = x.city;
int price = x.price;
int priceOfTrip = w.shortestDist + price;
if(priceOfTrip < v.shortestDist){ //relaxes the edge that it's on
cityQueue.remove(v);
v.shortestDist = priceOfTrip;
v.prev = w;
cityQueue.add(v);
}
}
}
}
你可以在代碼中指出Railroad.java:52行嗎? –
@AlexandreLavoie他做到了。 – chrylis
請發佈'Vertex'的代碼。我懷疑有些'Vertex'對象的'edges'字段沒有正確初始化。 – chrylis