將列名和行數據添加到表模型

Question

當我試圖將列名和行數據添加到表模型時，我得到空指針異常。列名來自列表，我將它們作爲數組添加到表模型中。但在那裏我得到異常：tableModel.addColumn(columnNames.toArray()); tableModel.addRow(rowData);

我全碼：

public class DBC extends JFrame{ 

static String tablo; 
static JTextField tf = new JTextField(20); 
static int columnCount; 
static JPanel tfPanel = new JPanel(); 
static String[] sutunlar; 
static JLabel sutunLabel; 
static JPanel sutunPanel = new JPanel(new BorderLayout()); 
static JTable table; 
static JScrollPane scrollPane; 
static DefaultTableModel tableModel; 
static Object[] columnNames; 

public static void main(String[] args) throws Exception { 

    Class.forName("com.mysql.jdbc.Driver"); 
    Connection connect = DriverManager.getConnection("jdbc:mysql://localhost:3306/project" 
       ,"root","123456789"); 

    final Statement statement = connect.createStatement(); 

    JLabel tabloSec = new JLabel("Tablo Seçin:"); 
    final JComboBox<String> tablolar = new JComboBox<String>(); 
    final DatabaseMetaData md = connect.getMetaData(); 
    final ResultSet rs = md.getTables(null, null, "%", null); 

    while (rs.next()) { 
     tablolar.addItem(rs.getString(3)); 
    } 

    tablolar.addActionListener(new ActionListener(){ 

     @Override 
     public void actionPerformed(ActionEvent arg0) { 

      tablo = tablolar.getSelectedItem().toString(); 

      try { 

       ResultSet rs2 = statement.executeQuery("SELECT * FROM "+tablo); 
       ResultSetMetaData rsmd = rs2.getMetaData(); 
       columnCount = rsmd.getColumnCount(); 
       List<String> columnNames = new ArrayList<String>(); 
       sutunlar = new String[columnCount]; 

       Object rowData[][] = {{""}}; 


        for(int i=0;i<columnCount;i++){ 

         sutunlar[i] = rsmd.getColumnLabel(i+1); 
         columnNames.add(sutunlar[i]); 
         tableModel.addColumn(columnNames.toArray()); 
         tableModel.addRow(rowData); 

         } 

        tableModel = new DefaultTableModel(rowData, columnNames.toArray()); 
        table = new JTable(); 
        table.setModel(tableModel); 
        table.repaint(); 
        scrollPane = new JScrollPane(table); 
        sutunPanel.add(scrollPane); 
        sutunPanel.revalidate(); 
        sutunPanel.repaint(); 


      } catch (SQLException e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
     } 
    }); 

    JButton ekle = new JButton("Ekle"); 
    ekle.addActionListener(new ActionListener(){ 

     @Override 
     public void actionPerformed(ActionEvent e) { 

      try { 
       switch(tablo){ 
       case "department": 

        statement.executeUpdate("INSERT INTO department(Name,Location) VALUES('"+tf.getText()+"')"); 
       case "employee": 

        statement.executeUpdate("INSERT INTO employee(Id,FirstName,LastName,Sex,Address,Email,Salary,BirthDate,JoinDate) VALUES('"+tf.getText()+"')"); 
       case "engineer": 

        statement.executeUpdate("INSERT INTO engineer(EngineerType) VALUES('"+tf.getText()+"')"); 
       case "manager": 

        statement.executeUpdate("INSERT INTO manager(Department) VALUES('"+tf.getText()+"')"); 
       case "project": 

        statement.executeUpdate("INSERT INTO project(Name,Number,Value) VALUES('"+tf.getText()+"')"); 
       case "secretary": 

        statement.executeUpdate("INSERT INTO secretary(TypingSpeed) VALUES('"+tf.getText()+"')"); 
       } 

      } catch (SQLException e1) { 
       // TODO Auto-generated catch block 
       e1.printStackTrace(); 
      } 
     } 
    }); 

    JButton cik = new JButton("Çık"); 
    cik.addActionListener(new ActionListener() { 

     @Override 
     public void actionPerformed(ActionEvent e) { 

      System.exit(0); 
     } 
    }); 

    JPanel panel = new JPanel(new FlowLayout()); 

    panel.add(tabloSec); 
    panel.add(tablolar); 
    panel.add(sutunPanel); 
    panel.revalidate(); 
    panel.add(ekle); 
    panel.add(cik); 

    JFrame frame = new JFrame("Deneme"); 
    frame.setSize(600,600); 
    frame.setLocationRelativeTo(null); 
    frame.add(panel); 
    frame.setVisible(true); 
    } 
} 

Answer 1

你需要訪問它之前實例tableModel。

Answer 2

您還沒有實例化您的tableModel 移動此代碼tableModel = new DefaultTableModel(rowData, columnNames.toArray());在for循環之前。