重新编辑：对不起，如果我将代码粘贴到pastebin。我不知道你们这么快就能解决问题。
所以我正在修改代码，在完成后我不知道为什么我做错了因为：
每次我在地图文件中添加一个条目而不是计算路径它在eigth节点上返回无穷大：它不会给出堆栈跟踪但是它会抛出：
Distance to Mandurriao: 0.0
Path: [Mandurriao]
Distance to Jaro: 79.0
Path: [Mandurriao, Jaro]
Distance to Iloilo: 118.0
Path: [Mandurriao, Jaro, Iloilo]
Distance to Leganes: 182.0
Path: [Mandurriao, Jaro, Leganes]
Distance to Tagbak: 81.0
Path: [Mandurriao, Tagbak]
Distance to Derp: 214.0
Path: [Mandurriao, Tagbak, Derp]
Distance to Herp: 305.0
Path: [Mandurriao, Tagbak, Derp, Herp]
Distance to Tugigarao: Infinity
Path: [Tugigarao]
每当我将地图文件设置为少于7个节点时，它就会给我：
Exception in thread "main" java.lang.NullPointerException
at Dijkstra.search(Dijkstra.java:81)
at Dijkstra.main(Dijkstra.java:132)
我是一个完整的java菜鸟，我一天前只制作了java代码。
所以这是代码：
import java.util.PriorityQueue;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
import java.io.*;
import java.util.*;
class Vertex implements Comparable<Vertex>
{
public final String name;
public Edge[] adjacencies;
public double minDistance = Double.POSITIVE_INFINITY;
public Vertex previous;
public Vertex(String argName) { name = argName; }
public String toString() { return name; }
public int compareTo(Vertex other)
{
return Double.compare(minDistance, other.minDistance);
}
}
class Edge
{
public final Vertex target;
public final double weight;
public Edge(Vertex argTarget, double argWeight)
{ target = argTarget; weight = argWeight; }
}
public class Dijkstra
{
public static void computePaths(Vertex source)
{
source.minDistance = 0.;
PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>();
vertexQueue.add(source);
while (!vertexQueue.isEmpty()) {
Vertex u = vertexQueue.poll();
// Visit each edge exiting u
for (Edge e : u.adjacencies)
{
Vertex v = e.target;
double weight = e.weight;
double distanceThroughU = u.minDistance + weight;
if (distanceThroughU < v.minDistance) {
vertexQueue.remove(v);
v.minDistance = distanceThroughU ;
v.previous = u;
vertexQueue.add(v);
}
}
}
}
public static List<Vertex> getShortestPathTo(Vertex target)
{
List<Vertex> path = new ArrayList<Vertex>();
for (Vertex vertex = target; vertex != null; vertex = vertex.previous)
path.add(vertex);
Collections.reverse(path);
return path;
}
///////////////////////////////////////////////////////////////////////////
public static int search(String [ ] numbers, String key)
{
for (int index = 0; index < numbers.length; index++)
{
if ( numbers[index].equals(key) )
return index; //We found it!!!
}
// If we get to the end of the loop, a value has not yet
// been returned. We did not find the key in this array.
return -1;
}
///////////////////////////////////////////////////////////////////////
public static void main(String[] args)
{
int MapLength = 0;
Vertex[] v = new Vertex[100];
String[] names = new String[100];
System.out.println("Initalized");
try {
int i = 0;
System.out.println("Initalized[0]");
FileInputStream fStream = new FileInputStream("f:\\map2.txt");
System.out.println("Initalized[1]");
BufferedReader in = new BufferedReader(new InputStreamReader(fStream));
System.out.println("Initalized[2]");
while (in.ready()) {
String parsed = "";
parsed = in.readLine();
String[] t = parsed.split(">");
if(t[0].equals("v")){
System.out.println("Added>" + parsed);
v[i] = new Vertex(t[1]);
names[i] = t[1];
i++;
MapLength = i;
}
if(t[0].equals("e")){
System.out.println("Initalized[3]");
int a;
int weight;
int ii = 0;
System.out.println("Initalized[4]." + t[1]);
String[] container = t[1].split("-");
System.out.println("Initalized[5]." + container);
Edge[] temp = new Edge[(container.length - 1) / 2];
for(a = 1; a < container.length; a +=2 ){
System.out.println("Initalized[6]." + names[search( names , container[ a ] )] + "...." + Integer.parseInt(container[ a + 1 ]));
temp[ii] = new Edge(v[ search( names , container[ a ] ) ], Integer.parseInt(container[ a + 1 ]));
ii++;
}
//System.out.println("Debug@LineCurrentNumberSearch: " + search( names , container[ a ] ) );
v[ search( names , container[ 0 ] ) ].adjacencies = temp;
}
}
in.close();
} catch (IOException e) {
System.out.println("File input error" + e);
}
/*
v[0] = new Vertex("Harrisburg");
v[1] = new Vertex("Baltimore");
v[2] = new Vertex("Washington");
v[3] = new Vertex("Philadelphia");
v[4] = new Vertex("Binghamton");
v[5] = new Vertex("Allentown");
v[6] = new Vertex("New York");
v[0].adjacencies = new Edge[]{ new Edge(v[1], 79.83), new Edge(v[5], 81.15) };
v[1].adjacencies = new Edge[]{ new Edge(v[0], 79.75),
new Edge(v[2], 39.42),
new Edge(v[3], 103.00) };
v[2].adjacencies = new Edge[]{ new Edge(v[1], 38.65) };
v[3].adjacencies = new Edge[]{ new Edge(v[1], 102.53),
new Edge(v[5], 61.44),
new Edge(v[6], 96.79) };
v[4].adjacencies = new Edge[]{ new Edge(v[5], 133.04) };
v[5].adjacencies = new Edge[]{ new Edge(v[0], 81.77),
new Edge(v[3], 62.05),
new Edge(v[4], 134.47),
new Edge(v[6], 91.63) };
v[6].adjacencies = new Edge[]{ new Edge(v[3], 97.24),
new Edge(v[5], 87.94) };
*/
Vertex[] vertices = new Vertex[MapLength];
int j;
for(j = 0; j < MapLength; j++){
vertices[j] = v[j];
}
computePaths(v[0]);
for (Vertex a : vertices)
{
System.out.println("Distance to " + a + ": " + a.minDistance);
List<Vertex> path = getShortestPathTo(a);
System.out.println("Path: " + path);
}
}
}
这是地图文件：
v>Mandurriao
v>Jaro
v>Iloilo
v>Leganes
v>Tagbak
v>Derp
v>Herp
v>Tugigarao
e>Mandurriao-Jaro-79-Tagbak-81
e>Jaro-Mandurriao-79-Iloilo-39-Leganes-103
e>Iloilo-Jaro-38
e>Leganes-Jaro-102-Tagbak-61-Derp-69
e>Tagbak-Derp-133
e>Derp-Mandurriao-81-Leganes-62-Tagbak-134-Herp-91
e>Herp-Leganes-97-Derp-87
e>Tugigarao-Herp-100
任何人都可以帮助我吗？提前谢谢。
答案 0 :(得分：1)
如果输入文件包含以下条目：
v>Mandurriao
v>Jaro
v>Iloilo
v>Leganes
v>Tagbak
v>Derp
e>Mandurriao-Jaro-79-Tagbak-81
e>Jaro-Mandurriao-79-Iloilo-39-Leganes-103
e>Iloilo-Jaro-38
e>Leganes-Jaro-102-Tagbak-61-Derp-69
e>Tagbak-Derp-133
顶点“Derp”没有任何相邻顶点，因此u.adjacency为null，导致小于7的条目的空指针异常。
答案 1 :(得分：0)
好的，只是为了向某人展示一些Google员工在这里偶然发现的事情。
它计入无穷大的原因是没有节点引用'Tugigarao'顶点因此没有显示它的路径。正如你可能会说的那样，你可以走出顶点，但由于没有参考或边缘，你无法进入。