Java GUI 使用从文本字段获取的参数创建对象

Question

所以我有这个 Jframe，您可以在其中填写文本字段，当单击“添加”时，它应该创建一个 Car 对象并将其发送到数据库。但在监听器中，即使我在字段中输入某种文本，我仍然在 textfieldname.getText() 上收到 java.lang.NullPointerException 。

这是 Jframe。

public void newCar()
   {

      JLabel make = new JLabel("Brand:");
      JTextField maket = new JTextField(10);

      JLabel model = new JLabel("Model:");
      JTextField modelt = new JTextField(10);

      JLabel license = new JLabel("License Plate Numbers:");
      JTextField licenset = new JTextField(10);

      JLabel color = new JLabel("Color:");
      JTextField colort = new JTextField(10);

      JLabel year = new JLabel("Year:");
      final JTextField yeart = new JTextField(10);
      yeart.addKeyListener(new KeyAdapter()
      {
         @Override
         public void keyTyped(KeyEvent e)
         {
            super.keyTyped(e);

            e.getKeyCode();

            if (!((int) e.getKeyChar() >= 48 && (int) e.getKeyChar() <= 57))
            {
               e.consume();
            }
         }

      });
      JLabel horse = new JLabel("Horse Power: ");
      JTextField horset = new JTextField(10);
      JLabel isAvailable = new JLabel("Car Status:");
      JLabel isAvailablet = new JLabel("Available");
      JLabel time = new JLabel("Time Until Service: ");
      JTextField timet = new JTextField(10);
      JLabel consumption = new JLabel("Consumption per 100km: ");
      JTextField consumptiont = new JTextField(10);
      JLabel seats = new JLabel("Number of Seats: ");
      JTextField seatst = new JTextField(10);
      seatst.addKeyListener(new KeyAdapter()
      {
         @Override
         public void keyTyped(KeyEvent e)
         {
            super.keyTyped(e);

            e.getKeyCode();

            if (!((int) e.getKeyChar() >= 48 && (int) e.getKeyChar() <= 57))
            {
               e.consume();
            }
         }

      });

      JLabel transmission = new JLabel("Transmission ");
      JComboBox transmissiont = new JComboBox<String>();
      JLabel climate = new JLabel("Climate Control: ");
      JComboBox climatet = new JComboBox<String>();

      JFrame window = new JFrame("New Car");

      JPanel newCarButtons = new JPanel();

      newCarButtons.setLayout(new FlowLayout());

      saveCar = new JButton("Save");
      saveCar.addActionListener(buttonListener);
      newCarButtons.add(saveCar);

      cancelCar = new JButton("Cancel");
      cancelCar.addActionListener(buttonListener);
      newCarButtons.add(cancelCar);

      JPanel newCarText = new JPanel();

      GroupLayout group = new GroupLayout(newCarText);
      newCarText.setLayout(group);

      group.setAutoCreateGaps(true);
      group.setAutoCreateContainerGaps(true);

      newCarText.add(make);
      newCarText.add(maket);

      newCarText.add(model);
      newCarText.add(modelt);

      newCarText.add(license);
      newCarText.add(licenset);

      newCarText.add(color);
      newCarText.add(colort);

      newCarText.add(year);
      newCarText.add(yeart);

      newCarText.add(horse);
      newCarText.add(horset);

      newCarText.add(isAvailable);
      newCarText.add(isAvailablet);

      newCarText.add(time);
      newCarText.add(timet);

      newCarText.add(consumption);
      newCarText.add(consumptiont);

      newCarText.add(seats);
      newCarText.add(seatst);

      JLabel doors = new JLabel("Number of Doors: ");
      JTextField doorst = new JTextField(10);

      doorst.addKeyListener(new KeyAdapter()
      {
         @Override
         public void keyTyped(KeyEvent e)
         {
            super.keyTyped(e);

            e.getKeyCode();

            if (!((int) e.getKeyChar() >= 48 && (int) e.getKeyChar() <= 57))
            {
               e.consume();
            }
         }

      });

      newCarText.add(doors);
      newCarText.add(doorst);

      transmissiont.addItem("Auto");
      transmissiont.addItem("Manual");

      transmissiont.addActionListener(buttonListener);

      newCarText.add(transmission);
      newCarText.add(transmissiont);

      climatet.addItem("Yes");
      climatet.addItem("No");

      newCarText.add(climate);
      newCarText.add(climatet);

      GroupLayout.SequentialGroup hGroup = group.createSequentialGroup();

      hGroup.addGroup(group.createParallelGroup().addComponent(make)
            .addComponent(model).addComponent(license).addComponent(color)
            .addComponent(time).addComponent(consumption).addComponent(year)
            .addComponent(horse).addComponent(isAvailable).addComponent(seats)
            .addComponent(doors).addComponent(transmission)
            .addComponent(climate));

      hGroup.addGroup(group.createParallelGroup().addComponent(maket)
            .addComponent(modelt).addComponent(licenset).addComponent(colort)
            .addComponent(timet).addComponent(consumptiont).addComponent(yeart)
            .addComponent(isAvailablet).addComponent(horset)
            .addComponent(seatst).addComponent(doorst)
            .addComponent(transmissiont).addComponent(climatet));

      group.setHorizontalGroup(hGroup);

      GroupLayout.SequentialGroup vGroup = group.createSequentialGroup();

      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(make).addComponent(maket));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(model).addComponent(modelt));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(license).addComponent(licenset));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(color).addComponent(colort));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(year).addComponent(yeart));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(horse).addComponent(horset));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(time).addComponent(timet));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(consumption).addComponent(consumptiont));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(isAvailable).addComponent(isAvailablet));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(seats).addComponent(seatst));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(doors).addComponent(doorst));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(transmission).addComponent(transmissiont));
      vGroup.addGroup(group.createParallelGroup(Alignment.BASELINE)
            .addComponent(climate).addComponent(climatet));

      group.setVerticalGroup(vGroup);

      JPanel newCar = new JPanel();
      newCar.setLayout(new BorderLayout());

      newCar.add(newCarText, BorderLayout.NORTH);
      newCar.add(newCarButtons, BorderLayout.SOUTH);

      newCar.setBorder(new TitledBorder(BorderFactory
            .createLineBorder(Color.black), "[New Car]", 2, 0));


      window.add(newCar);
      window.setLocationRelativeTo(null);
      window.setSize(400, 450);
      window.setVisible(true);

   }

按钮监听器:(忽略输入的值，我只是测试对象是否已发送，所以我必须输入一些值，因为我遇到了 .getText() 的问题)

 private class MyButtonListener implements ActionListener
   {
      public void actionPerformed(ActionEvent e)
      {
         if (e.getSource() == addCars)
         {
            newCar();

         }

         if (e.getSource() == saveCar)
         {
            adapter = new DatabaseAdapter2();

            // Car car1 = new Car("ss", "ss",
            // "sd", "ss",
            // 15, "ss","ss",
            // "ss", "ss", 2, 2, "ss",
            // "ss", 2);

            Car car1 = new Car(maket.getText(), "test", "test", "test", 2011,
                  "test", "test", "test", "test", 2011, 2011, "test", "test", 2);
            System.out.println(car1);

            adapter.addCar(car1);
         }
         if (e.getSource() == cancelCar)
         {

         }

         if (e.getSource() == getCars)
         {

         }
         if (e.getSource() == removeCars)
         {

         }
         if (e.getSource() == editCars)
         {

         }
         if (e.getSource() == infoCars)
         {

         }
         if (e.getSource() == addClients)
         {
            newClient();
         }
         if (e.getSource() == removeClients)
         {

         }
         if (e.getSource() == editClients)
         {

         }
         if (e.getSource() == infoClients)
         {

         }
         if (e.getSource() == addAutoCampers)
         {

         }
         if (e.getSource() == removeAutoCampers)
         {

         }
         if (e.getSource() == editAutoCampers)
         {

         }
         if (e.getSource() == infoAutoCampers)
         {

         }
         if (e.getSource() == addBookings)
         {
            newBooking();
         }
         if (e.getSource() == removeBookings)
         {

         }
         if (e.getSource() == editBookings)
         {

         }
         if (e.getSource() == infoBookings)
         {

         }

         // if (e.getSource() == transmissiont)
         // {
         // if (transmissiont.getSelectedItem())
         // {
         // Student temp = (Student)studentBox.getSelectedItem();
         // firstNameField.setText(temp.getFirstName());
         // lastNameField.setText(temp.getLastName());
         // }
         // }

      }
   }
}

Answer 1

您似乎遇到了上下文问题。

您已在 newCar 方法中声明了所有字段，这意味着您在屏幕上使用的字段与您在 newCar 中访问的字段不同>actionPerformed 方法。

尝试删除变量名称之前的 JTextField(在 newCar 方法中)，并在需要时将缺少的字段声明为实例变量

您还应该避免在文本字段上使用 KeyListener，当您收到按键事件通知时，它已经应用于字段 Document。

相反，您应该考虑使用DocumentFilter

查看

• Text Component Features
• DocumentFilter examples