Question

我在eclipse中遇到了一个令人困惑的错误，但是在命令行linux帐户的主服务器上却没有。所有代码都在eclipse的主src目录中。代码在命令行编译，但在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)

代码

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"));

    }

}

Graph.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;
    }
}

Vertex.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环境以不同于命令行环境的方式处理代码。该课程是一门课程正在进行中。我只想解决看起来像Eclipse的错误。

Answer 1

看起来eclipse有Graph.class的旧版本。您应该尝试清理项目：请参阅问题Function of Project > Clean in Eclipse

Answer 2

代码在命令行编译但在Eclipse中产生此错误

可能的解决方案： 1）确保eclipse使用与通过命令行使用的代码相同的代码。 2）在eclipse中进行干净的构建，因为案例可能就像它仍然引用旧的类文件一样，无论源已被更改。

Answer 3

当你运行时，在类路径中找不到Graph.class。

java.lang.NoSuchMethodError：Graph：method <init>（）V not found </init>

3 个答案: