Java- java.lang.NoClassDefFoundError，类路径不是问题

Question

I'm writing a program for homework and running into an issue I can't seem to resolve. The problem involves simulating the probabilities of a randomwalk ending on any given node (just background, not really relevant to the problem). I've written my own class that uses a hash map to hold node objects (UndirectedGraph and NodeEntry respectively). I've also written a test harness.

Originally all these were in one file but I decided to move the UndirectedGraph and NodeEntry to a separate package...cause that seems like the right thing to do. I've gotten everything fixed up so that testHarness will compile but at runtime I get the following:

Exception in thread "main" java.lang.NoClassDefFoundError: GraphWalker/NodeEntry
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2531)
at java.lang.Class.getMethod0(Class.java:2774)
at java.lang.Class.getMethod(Class.java:1663)
at sun.launcher.LauncherHelper.getMainMethod(LauncherHelper.java:494)
at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:486)
Caused by: java.lang.ClassNotFoundException: GraphWalker.NodeEntry
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    ... 6 more

from looking around I find a few answers for this, primarily that the classes aren't on the classpath. Thing is I have all these files in the same folder, and my understanding is the current folder is always on the classpath.

here's abbreviated copies of the code:

testHarness:

import java.util.*;
import GraphWalker.*;

public class testHarness {

    public static void main (String args[]) {
        new testHarness();
    }


    public testHarness() {
        GraphWalker.UndirectedGraph graph = new GraphWalker.UndirectedGraph(3);
//      System.out.println(graph.containsNode(1));
        graph.addNode(1);
        graph.addNode(2);
        graph.addNode(3);

UndirectedGraph:

package GraphWalker;
import java.util.*;

public class UndirectedGraph {

    /* 
     * Based in part on UndirectedGraph.java by Keith Schwarz (htiek@cs.stanford.edu) 
     */

    public HashMap graphMap;

    public UndirectedGraph(int numNodes) {
        this.graphMap = new HashMap(numNodes);
    }

    public void addNode (Integer nodeNum) {
        graphMap.put(nodeNum, new NodeEntry(1.0f,0.0f));
    }

NodeEntry:

package GraphWalker;
import java.util.*;


public class NodeEntry {

    // four inherent values
    // credit is the current credit of the node
    // nextCredit holds the credit for the next step
    // adjList holds a list of adjacent node IDs 
    // degree holds the number of neighbors
    public Float credit;
    public Float nextCredit; 
    public ArrayList adjList;
    public Integer degree;


    public NodeEntry(Float credit, Float nextCredit) {
        this.credit = credit;
        this.nextCredit = nextCredit;
        this.adjList = new ArrayList();
        this.degree = 0;
    }


    public void addEdge(Integer neighbor) {
        this.adjList.add(neighbor);
        this.degree += 1;
    }

each class has quite a bit more code but I don't think it's relevant to the issue. I'm working on Ubuntu 12.04 and trying to compile and run from both command line and using Geany (simple IDE) same behavior either way.

Any help?

Answer 1

Alrighty, The issue was that the package files needed to be in a separate folder (named for the package, in my case GraphWalker). I'm not entirely clear on why it compiled fine but at runtime when it went to look for the package it seems to have expected/required them to be in their own folder.

I wouldn't consider that a class path issue, per se, since the files being looked for were in a folder that was on the classpath, just not the folder they needed to be in.