QueryTableModel

Programação Java
#1

galera estou com probs com a minha classe que contrui pra entrar no db, acessar as infos da tabela e montar em uma JTable:


Connection con;
  String url;
  String driver;
  Statement stmt;
  Vector cache;  // will hold String[] objects . . .
  int colCount;
  String[] headers;
  String currentURL;

  public QueryTableModel() {
    cache = new Vector();
  }

    @Override
  public String getColumnName(int i) { return headers[i]; }
  public int getColumnCount() { return colCount; }
  public int getRowCount() { return cache.size();}

  public Object getValueAt(int row, int col) {
    return ((String[])cache.elementAt(row))[col];
  }

  public void setHostURL(String url) {
    if (url.equals(currentURL)) {
      // same database, we can leave the current connection open
      return;
    }
   
    closeDB();
    initDB(url);
    currentURL = url;
  }

  // All the real work happens here; in a real application,
  // we'd probably perform the query in a separate thread.
  public void setQuery(String q) {
    cache = new Vector();
    try {
      // Execute the query and store the result set and its metadata
      ResultSet rs = stmt.executeQuery(q);
      ResultSetMetaData meta = rs.getMetaData();
      colCount = meta.getColumnCount();

      // Now we must rebuild the headers array with the new column names
      headers = new String[colCount];
      for (int h=1; h <= colCount; h++) {
        headers[h-1] = meta.getColumnName(h);
      }

      // and file the cache with the records from our query.  This would not be
      // practical if we were expecting a few million records in response to our
      // query, but we aren't, so we can do this.
      while (rs.next()) {
        String[] record = new String[colCount];
        for (int i=0; i < colCount; i++) {
          record[i] = rs.getString(i + 1);
        }
        cache.addElement(record);
      }
      fireTableChanged(null); // notify everyone that we have a new table.
    }
    catch(Exception e) {
      cache = new Vector(); // blank it out and keep going.
      e.printStackTrace();
    }
  }

  public void initDB(String url) {

    url = "jdbc:odbc:controlePortas";
        driver = "sun.jdbc.odbc.JdbcOdbcDriver";

        try {
            Class.forName(driver);
            con = DriverManager.getConnection(url);
            JOptionPane.showMessageDialog(null, "Conectado ao banco");

            stmt = con.createStatement();

        } catch (ClassNotFoundException e) {
            System.err.println("");
            e.printStackTrace();
        } catch (SQLException sqlex) {
            System.err.println("");
            sqlex.printStackTrace();
        }
  }

  public void closeDB() {
    try {
      if (stmt != null) { stmt.close(); }
      if (con != null) {        con.close(); }
    }
    catch(Exception e) {
      System.out.println("Could not close the current connection.");
      e.printStackTrace();
    }
  }
}

mas ele tah dando o erro de nullpointer excepiton quando eu a executo na classe prncipal, será que al poderia me ajudar!?!

#2