求教 求教 ，txt读取 ，然后存入树中. 为什么呢？为什么呢？求解啊～高手们 ...

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(element.compareTo(p.getData())<0)
                p.setLeft(addNode(element,p.getLeft()));
            
            else if(element.compareTo(p.getData())>0)
                p.setRight(addNode(element,p.getRight()));
            
            else
                p.setData(element);
               
            return p;
        }
}