这个JAVA代码老是在运行前有各种NULL POINTER EXCEPTION，求高手帮忙！！

[bahamter]

这个JAVA代码是我自己写的。新人。目的是做一个并发的哈密圈寻路系统。但是有好多好多的Null pointer exception和小问题。求高手帮忙！！给大家磕头了！！
这是NODE的代码。

import java.util.*;


/**
* Title: Node.java
* Description: Every Node can do the same job as Worklist down.because this node just process there own solution, so the solution set is not necessary
*
*
* Copyright: Copyright (c) 2001
* Company: Bond University
* @author Chi Zhang
* @version 1.0 25/10/01
*/

class Node implements Runnable
{
protected Graph graph;
protected Vector buffer=new Vector();
protected String name;
protected Set contents; // Information stored at this node
private volatile boolean stop;
private Node dest[];
private Vector sources;
private Vector collection;
private Path oldPath;
private Warning[] allWarn=new Warning[10];
private boolean askEnd = false;
private Message[] messageCollection = new Message[10];
private Iterator nodeIter = contents.iterator();
/**
* * Constructors
*/
public Node(String n, Set c)
{
name = n;
contents = c;
}
public Node(String n)
{
name = n;
}
/**
* some graphiv method;
*/
public void setGraph(Graph g)
{
graph = g;
dest = g.getDestinations(this);
for (int i = 0; i< dest.length;i++)
{
allWarn[i]= new Warning(dest[i]);
}
for (int i = 0; i< dest.length;i++)
{
messageCollection[i]= new Message(dest[i]);
}
}

public Node() { name = ""; }
public String getName() { return name; }
public Object getContents() { return contents; }
public void setContents(Set o) { contents = o; }
public boolean isEmpty() { return (contents == null); }
public boolean equals(Node input){return ((input.getName()).equals(name));}
public String toString() { return getName(); }
public void getOn(){stop =true;}
/**
* it's the input buffer;
*/
public Vector getBuffer(){return buffer;}
/**
* check the path is whether a HamiltonianCycle.
*/
private boolean isHamiltonianCycle(Path p, Graph g)
{
return ( p.hasCycle() && p.length() == g.size()+1 && p.first().equals(p.last()) );
}
/**
* main method in the program. all program about the buffer control.
*/
public void processBuffer() throws InterruptedException
{
Message a = (Message)buffer.get(0);
if (a.getMission().equals(askEnd))//check whether this an end message
{
synchronized(this)
{
buffer.remove(0);
for (int i = 0;i<messageCollection.length;i++)
{
if ((messageCollection[i].getSource()).equals(a.getSource()))//save the last receive message into every sender code.
{
messageCollection[i].setMission(a.getMission());
}
}
notify();
}// wake up the thread(s) waiting for the buffer to empty
}
else
{
synchronized(this)
{
buffer.remove(0);
notify(); // wake up the thread(s) waiting for the buffer to empty
}
Set ss = (Set)a.getMission();//get the input code.
Node n = a.getSource();
if (contents.contains(ss))//if this is already in the solution.
{
for (int i = 0;i<dest.length;i++)
{
if (allWarn[i].getPosition()== n)//set the warning if receive an old solution.
{
allWarn[i].setAnswer(false);
}
}
}
else
{
for (int i = 0;i<messageCollection.length;i++)//change the last receive message
{
if ((messageCollection[i].getSource()).equals(a.getSource()))
{
messageCollection[i].setMission(a.getMission());
}
}
for (int i = 0;i<dest.length;i++)
{
if (allWarn[i].getPosition()== n)
{
allWarn[i].setAnswer(true);
}
}
contents.addAll(ss);
if (!contents.isEmpty())
{
Set out = calcOutSet(this, ss);
contents = out;
for(int i= 0; i<dest.length;i++)
{
Message message = new Message(this, out);
dest[i].add(a);
}
}
}
}
}
/**
* check the solution and send this solution to every linked node.
*/
private Set calcOutSet(Node n, Set in)
{
Set out = new HashSet();
Iterator paths = in.iterator();
while (paths.hasNext())
{
Path p = (Path) paths.next();
if (!isHamiltonianCycle(p, graph))
{
// References to paths stored in sets. Therefore need to make a new path object to
// avoid unwanted changes through aliases
p = new Path(p);
p.add(n);
}
if (propagate(p))
{
out.add(p);
oldPath = p;
}
}
return (out);
}
/**
* check the path whether can be sperate.
*/
private boolean propagate(Path p)
{
return ((!oldPath.equals(p))&&(isHamiltonianCycle(p, graph) || !p.hasCycle()) );
}
public synchronized void add(Message p)
{
buffer.add(p);
notify();
}
/**
* define how to run the each node.
*/
public synchronized void run()
{
try
{
while(!stop)
{
if(buffer.isEmpty()!=true)
{processBuffer();}
else
for (int i = 0; i<dest.length;i++)
{
Message askStop = new Message(this,askEnd);
dest[i].add(askStop);
}
wait();
}
}catch(InterruptedException ie){return;}
}
/**
* define how to finish.
*/
public void finish()
{
synchronized(this)
{
while(checkEnd()!= true||(buffer.isEmpty()!= true)||(otherWarning()!=true))//only if receive no new information and input buffer
try{wait();}catch(InterruptedException ie){} //is empty and receive all and request
stop = true;
notify();
}
}
/**
* check whether recieve no new information
*/
public boolean checkEnd()
{
for(int i = 0; i< allWarn.length; i++)
{
if (allWarn[i].getAnswer()!=true){return false;}
}
return true;
}
/**
* send the end request
*/
public boolean otherWarning()
{
for (int i=0;i<messageCollection.length;i++)
{
if ((messageCollection[i].getMission()).equals(askEnd)!=true){return false;}
}
return true;
}
/**
* use to print
*/
public String toResult()
{
String s = "{";
Iterator solIt = nodeIter;
while (solIt.hasNext())
s += solIt.next() + ", ";
return ( ((s.length() > 1) ? s.substring(0,s.length()-2) : s) + "}");
}
}
/**
* build a class to tell others the warning;
*/
class Warning
{
protected Node position;
protected boolean judge;
/**
* basic stucture.
*/
public Warning(Node n)
{
position=n;
judge = false;
}
public Warning(Node n, boolean b)
{
position = n;
judge = b;
}
/**
* basic method;
*/
public Node getPosition() { return position; }
public boolean getAnswer() { return judge; }
public void setAnswer(boolean a){judge = a;}
}

[bahamter]

这个是我的主程序代码！！

import java.util.*;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.Vector;

/**
* Title: HamiltonSolver.java
* Description: use a Concurrency to make it work
*
* Copyright: Copyright (c) 2001
* Company: Bond University
* @author Chi Zhang
* @version 1.0 26/10/01
*/
/**
* check Graph to get Nodes and Connections
*/
public class HamiltonSolver
{
public Graph graph;
public Vector allNode;
/**
* main method
*/
public void solve()
{
Graph graph = new Graph();
String result = "";
Node [] list = new Node[graph.size()];//get all node and save them into the input buffer.
Iterator it = graph.nodesIterator();
while(it.hasNext())
{
int i = 0;
list[i] = (Node)it.next();
Node [] dests = graph.getDestinations(list[i]);
for (int a = 0; a < dests.length; a++)
{
Path startLine = new Path(dests[a]);
Message beginning = new Message(list[i],startLine);
list[i].add(beginning);
}
i++;
}
for (int count = 0; count<graph.size(); count++)//start the threads
{
new Thread(list[count]).start();
}
System.out.println(list[0].toResult());//print the result
}
}

[bahamter]

这个是Message部分
/**
* this message just used to transfer information between nodes
*
* @author (Chi Zhang)
* @version (2.0)
*/
import java.util.*;
public class Message
{
/**
* the message mast have the set of path and the source node.
*/
protected Node source;
protected Object mission;
public Message(Node o, Object n)
{
source = o;
mission = n;

}
public Message(Node o)
{
source = o;
mission = null;
}
/**
* basic methods.
*/
public Node getSource(){return source;}
public Object getMission(){return mission;}
public void setMission(Object ss){mission =ss;}
/**
* check two method whether is same.
*/
public boolean equals(Message a)
{
if (source.equals(a.getSource())
&&mission.equals(a.getMission()))
{return true;}
else return false;
}

}

[bahamter]

这个是Path

import java.util.Iterator;
import java.util.Vector;
import java.lang.Cloneable;

/**
* Title: Path.java
* Description: Represents a path in a graph as a sequence of nodes
* I only increase a equals method
* Copyright: Copyright (c) 2001
* Company: Bond University
* @author Chi Zhang
* @version 1.0 25/10/01
*/

public class Path {

/**
* The nodes in the path are stored in a vector
*/
protected Vector elements;

public Path() { elements = new Vector(); }
public Path(Node n) { this(); this.add(n); }

/**
* This constructor makes a new path have the same node sequence as another
*
* @param p the path to copy
*
*/
public Path(Path p) {
this();
Iterator it = p.elements.iterator();
while (it.hasNext())
elements.add(it.next());
}


/**
* Add a node to the end of the path
*
* @param n the node to add
*/
public void add(Node n) { elements.add(n); }
/**
* check two Path whether can be equals;
*/
public boolean equals(Path p)
{
Iterator it1 = p.elements.iterator();
Iterator it2= elements.iterator();
while (it1.hasNext()||it2.hasNext())
{
it1.next();
it2.next();
if(it1.equals(it2)!=true)
return false;
}
return true;
}

/**
* Determine if the node is already in the path
*
* @param n the node being checked
* @return whether the node is in the path or not
*/
public boolean contains(Node n) { return (elements.contains(n)); }

/**
* Determine if the path contains a cycle
* - a path contains a cycle if the same node is in the path more than once
*
* @return whether or not the path contains a cycle
*/
public boolean hasCycle() {
boolean cycle = false;
Iterator it = elements.iterator();
while (!cycle && it.hasNext()) {
Object next = it.next();
cycle = (elements.indexOf(next) != elements.lastIndexOf(next));
}

return (cycle);
}


/**
* Access the first and last nodes of the path
*
* @return first/last node in path
*/
public Node first() { return ((Node) elements.firstElement()); }
public Node last() { return ((Node) elements.lastElement()); }


/**
* Determine the length of the path
*
* @return the path length
*/
public int length() { return (elements.size()); }
public boolean isEmpty()
{
if (elements.size()==0)
return true;
return false;
}


/**
* String representation of a path is sequence of node names
*
* @return the string representation
*/
public String toString() {
Iterator it = elements.iterator();
String s = "<";
while (it.hasNext())
s += ((Node) it.next()).getName() + ",";

return ( ((s.length() > 1) ? s.substring(0,s.length()-1) : s) + ">");
}
}

[火龙果被占用了]

这 4 大层楼的代码估计没人会看的。

空指针异常基本上是由于在编写代码时很不好编码习惯造成的。比如说从方法中传进来的参数，不检查是否为 null 就直接拿来使用了。

[pf_renren]

把报错详细信息发上来

行数

[godismydaughter]

应该是没人会一句一句看的。

[crazylaa]

Graph这不知哪里的。Node.java有一堆东西没有import。。。

[frank3G]

加油加油，我支持LZ

[老张-AI]

public class NullPointerException
extends RuntimeException
当应用程序试图在需要对象的地方使用 null 时，抛出该异常。这种情况包括： 

调用 null 对象的实例方法。 
访问或修改 null 对象的字段。 
将 null 作为一个数组，获得其长度。 
将 null 作为一个数组，访问或修改其时间片。 
将 null 作为 Throwable 值抛出。 
应用程序应该抛出该类的实例，指示其他对 null 对象的非法使用。 

[mycity21]

一打开这个页面,我马上把它拖到最下边.发了这么多代码,却不把错误信息贴出来.很少有人会从头到尾看代码,帮你找出错误的.

[godismydaughter]

[Quote=引用 9 楼 zl3450341 的回复:]
Java codepublicclass NullPointerExceptionextends RuntimeException
当应用程序试图在需要对象的地方使用null 时，抛出该异常。这种情况包括：

调用null 对象的实例方法。
访问或修改null 对象的字段。
将null 作为一个数组，获得其长度。
将null 作为一个数组，访问或修改其时间片。
将null 作为 Throwable 值抛出。
应用程序应该抛出该类的实例，指示其他对null 对象的非法使用。

[/Quote]很好，好详细

[fengboxjtu556]

[Quote=引用 9 楼 zl3450341 的回复:]
Java codepublicclass NullPointerExceptionextends RuntimeException
当应用程序试图在需要对象的地方使用null 时，抛出该异常。这种情况包括：

调用null 对象的实例方法。
访问或修改null 对象的字段。
将null 作为一个数组，获得其长度。
将null 作为一个数组，访问或修改其时间片。
将null 作为 Throwable 值抛出。
应用程序应该抛出该类的实例，指示其他对null 对象的非法使用。

[/Quote]

已经很详细了，还有很多种情况，这要在实际工作总总结

[hllf6031]

恩，楼主还是将错误信息发出来就好了