我在 Eclipse 中遇到了一个令人困惑的错误，但在命令行 linux 帐户中的主服务器上却没有。所有代码都在主 src 目录中，在 eclipse 中。代码在命令行编译，但在我的 Mac OS X 笔记本电脑上的 Eclipse 中产生此错误：
Exception in thread "main" java.lang.NoSuchMethodError: Graph: method <init>()V not found
at Lab17.main(Lab17.java:11)
编码
Lab17.java
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.util.Scanner;
public class Lab17 {
// Lab17 first attempt at creating a graph
public static void main(String[] args) throws Exception {
Graph myGraph = new Graph();
URLConnection conn = null;
try {
URL url = new URL("http://csc.mendocino.edu/~jbergamini/222data/flights/flights");
conn = url.openConnection();
} catch (IOException e) {
System.out.println("Unable to open Flights file");
System.exit(1);
}
Scanner s = null;
try {
s = new Scanner(conn.getInputStream());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
while (s.hasNext()) {
String src = s.next();
String dst = s.next();
s.next();
double cost = s.nextDouble();
//System.out.println(src+" "+dst+" "+cost);
myGraph.addEdge(src, dst, cost);
}
System.out.println(myGraph.breadthFirst("Austin", "Washington"));
System.out.println(myGraph.depthFirst("LosAngeles", "Washington"));
System.out.println(myGraph.breadthFirst("LosAngeles", "Washington"));
System.out.println(myGraph.depthFirst("Washington", "LosAngeles"));
System.out.println(myGraph.breadthFirst("Washington", "LosAngeles"));
}
}
图.java
import java.util.LinkedList;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.TreeMap;
public class Graph {
private TreeMap<String, Vertex> vertexMap;
/** Creates a new, empty graph */
public Graph() {
// create vertexMap for Graph
vertexMap = new TreeMap<String, Vertex>();
}
/**
* Adds an edge
* @param src the source vertex
* @param dst the destination vertex
* @param cost the weight of the edge
*/
public void addEdge(String src, String dst, double cost) {
//System.out.println(src+" "+dst+" "+cost+" in Graph()");
// check to see if there is a src vertex
if(vertexMap.get(src) == null) {
// if src Vertex does not exist create Vertex for src
vertexMap.put(src, (new Vertex(src)));
//System.out.println(vertexMap.get(src).toString());
}
// check to see if there is a dst Vertex
if(vertexMap.get(dst) == null) {
// if dst Vertex does not exist create Vertex for dst
vertexMap.put(dst, (new Vertex(dst)));
//System.out.println(vertexMap.get(dst).toString());
}
// populate the dst and cost for Edge on the src Vertex vertexMap element
Vertex srdVertex = vertexMap.get(src);
Vertex dstVertex = vertexMap.get(dst);
Edge sEdge = new Edge(dstVertex, cost);
srdVertex.addEdge(sEdge);
}
/** Clears/empties the graph */
public void clear() {
vertexMap = new TreeMap<String,Vertex>();
}
/**
* Traverses, depth-first, from src to dst, and prints the vertex names in the order visited.
* @param src the source vertex
* @param dst the destination vertex
* @return whether a path exists from src to dst
*/
public boolean depthFirst(String src, String dst) {
System.out.println("Depth-first from "+src+" to "+dst);
for(Map.Entry<String,Vertex> entry: vertexMap.entrySet()) {
String key = entry.getKey();
Vertex thisVertex = entry.getValue();
System.out.println(key + " => " + thisVertex.toString());
}
return false;
}
/**
* Traverses, breadth-first, from src to dst, and prints the vertex names in the order visited
* @param src the source vertex
* @param dst the destination vertex
* @return whether a path exists from src to dst
*/
public boolean breadthFirst(String src, String dst) {
System.out.println("Breadth-first from "+src+" to "+dst);
// find starting vertex in vertexMap
Vertex start = vertexMap.get(src);
LinkedList<Vertex> vertexQue = new LinkedList<Vertex>();
LinkedList<Vertex> visitedV = new LinkedList<Vertex>();
// check it for null
if( start == null) {
throw new NoSuchElementException(" Start vertex not found");
}
// create a Queue for searching through vertex edges
//Queue<Vertex> q = new Queue<Vertex>();
vertexQue.add( start );
start.dest = 0;
boolean found = false;
while( !vertexQue.isEmpty() && !found) {
Vertex v = vertexQue.removeLast();
if( v.toString() == dst) {
// print queue
found = true;
}
else if(!visitedV.contains(v)){
// put all the adj vertex's into the queue
for( Edge e: v.getEdges() ) {
Vertex w = e.getDst();
vertexQue.add( w );
}
}
// add v to visitedV linked list
if(!visitedV.contains(v)){
visitedV.add(v);
}
}
System.out.print("[");
for(int i=0; i < visitedV.size(); i++) {
System.out.print(visitedV.get(i)+", ");
}
System.out.println("]");
/*forVertex> entry: vertexMap.entrySet()) {
String key = entry.getKey();
Vertex thisVertex = entry.getValue();
System.out.println(key + " => " + thisVertex.toString());
for(Edge e : thisVertex.getEdges() ){
System.out.print(e.toString());
}
System.out.println();
System.out.println("All Edges Evaluated");
}*/
return false;
}
}
顶点.java
import java.util.Set;
import java.util.TreeSet;
public class Vertex {
private String name;
private TreeSet<Edge> adj;
public double dest;
/**
* Creates a new vertex
* @param name the name of the vertex
*/
public Vertex(String name) {
this.name = name;
adj = new TreeSet<Edge>();
}
public TreeSet<Edge> getEdges() {
return this.adj;
}
/**
* Returns the set of all edges starting from this vertex.
* Set shall be ordered with respect to the names of the destination vertices.
*/
public Set<Edge> allAdjacent() {
Set<Edge> vertexSet = adj;
return null;
}
public String toString() {
return name;
}
public void addEdge(Edge e) {
this.adj.add(e);
}
}
public class Edge implements Comparable<Edge> {
private Vertex dst;
private double cost;
/** Creates a new edge with an associated cost
* @param dst the destination vertex
* @param cost the weight of the edge
*/
public Edge(Vertex dst, double cost) {
this.dst = dst;
this.cost = cost;
}
public Vertex getDst() {
return dst;
}
@Override
public int compareTo(Edge o)
{
if(o == null)
return -1;
if(this == null)
return -1;
if( this.dst.toString().compareTo( ((Edge)o).dst.toString() ) == 0 )
return 0;
else if ( this.dst.toString().compareTo( ((Edge)o).dst.toString() ) < 0 )
return 1;
else
return -1;
}
public String toString() {
String theEdgeS = this.dst.toString()+" "+Double.toString(cost);
return theEdgeS;
}
}
不确定为什么 Eclipse 环境对代码的处理方式与命令行环境不同。班级是班级正在进行的工作。我只是想解决看起来像 Eclipse 的错误。