我想将读取一个.txt 中的记录，例如
6274  John         Johnson         315.56
2843  Mark            Wilson          7217.23
4892  Dana           Albright     31462.56

将每一行记录，生成一个 Employee 类的 object .
然后将它存入 Binary Search Tree 中...一条一条加入树中。
但是在存入树中时，抛出了一个 NullPointer 异常。
实在不解，为什么？

public class Lab5
{
   public static void main (String[] args) throws IOException
   {
      Company company = new Company();
      company.menu("1 - Employees.txt");
    }
}

public class Company
{
    public void menu(String line)throws IOException
    {
        String delim = "- \r\t";
        String file = "";
        int id = 0;
        String lastName="" , firstName= "";
        double salary = 0.0;
        TreeBag bsTree = null;
        
        StringTokenizer tokenizer  = new StringTokenizer(line,delim);
        int command = Integer.parseInt(tokenizer.nextToken());
        
        switch(command)
        {            
            case 1:  //创建一个树，然后将.txt中的记录存入。
                while(tokenizer.hasMoreTokens())
                {
                    file     = tokenizer.nextToken();
                }
                BufferedReader fileIn = new BufferedReader(new FileReader(file));
                String record = fileIn.readLine();
                while(record != null )
                {
                    StringTokenizer tokenizer2 = new StringTokenizer(record);                
                    while(tokenizer2.hasMoreTokens())
                    {
                        id        = Integer.parseInt(tokenizer2.nextToken());
                        lastName  = tokenizer2.nextToken();
                        firstName = tokenizer2.nextToken();
                        salary    = Double.parseDouble(tokenizer2.nextToken());    
                        Employee employee = new Employee(id,lastName,firstName,salary);    
                        //System.out.println( employee.tostring());
                        bsTree.add(employee);//这里抛出nullpointer 异常
                    }
                    record = fileIn.readLine();             
                }
                break;

                                ......
                            }//end switch
                        }//end main
}//end class 



public class TreeBag
{
        private BTNode root ;
        
        public TreeBag()
        {
            root = null;
        }

        public void add(Comparable element)
        {
            addNode(element,root);
        }
        
        public BTNode addNode(Comparable element , BTNode p)
        {
            if(p == null)
                p = new BTNode(element, null ,null);
            
            else if((p.getData())<0)
                p.setLeft(addNode(element,p.getLeft()));
            
            else if((p.getData())>0)
                p.setRight(addNode(element,p.getRight()));
            
            else 
                p.setData(element);
                
            return p;
        }
}

除此之外，当然有 个class  BTNode {...}  ， 就不列不来了。

找到错误了.....晕！

仔细！
我也经常犯错误！

是啊。有错误才会进步啊。