Question

我基本上为简单的烘焙程序构建了一个简单的GUI。问题是在为JTable创建模型后，添加一行数据 model.addRow(new String[] {"data", "data","data", "data"});

在actionlistener中不起作用：

public void actionPerformed(ActionEvent event) {
   String buttonText = event.getActionCommand();

if (buttonText.equals("Create Savings Account")) {
     createSavingsAccount();

  public void createCreditAccount() {
    logic.createCreditAccount(pNrField.getText());
    model.addRow(new String[] {"data", "data","data", "data"});
  }

如果我尝试创建帐户，我会收到此消息：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at svimag6.GUImain.createSavingsAccount(GUImain.java:145)
    at svimag6.GUImain.actionPerformed(GUImain.java:124)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at svimag6.GUImain.createSavingsAccount(GUImain.java:145)
    at svimag6.GUImain.actionPerformed(GUImain.java:124)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at svimag6.GUImain.createCreditAccount(GUImain.java:140)
    at svimag6.GUImain.actionPerformed(GUImain.java:128)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at svimag6.GUImain.createCreditAccount(GUImain.java:140)
    at svimag6.GUImain.actionPerformed(GUImain.java:128)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

但是，如果我硬编码将新行添加到表中，（在构造函数中）它可以工作。但我无法动态添加数据。

以下是代码：

package gui;

import javax.swing.*;
import javax.swing.table.DefaultTableModel;

import java.awt.event.*;
import java.awt.*;

//YOU NEED TO ADD A FIELD in the GUI FOR NAME, LASTNAME AND PNR

public class GUImain extends JFrame implements ActionListener {

  private static final long serialVersionUID = 1L;
  private BankLogic         logic;
  private JList<Object>     customerList;
  private JTable            accountTable;
  private JTable            transactionTable;
  private JTextField        nameField;
  private JTextField        lastnameField;
  private JTextField        pNrField;


  private DefaultTableModel model;
  private DefaultTableModel model1;
  private JButton addButton                  = new JButton("Add Customer");
  private JButton showButton                 = new JButton("Show");
  private JButton clearButton                = new JButton("Rensa");
  private JButton createSavingsAccountButton = new JButton("Create Savings Account");
  private JButton createCreditAccountButton  = new JButton("Create Credit Account");
  private JButton deleteAccountButton        = new JButton("Delete Account");
  private JButton withdrawButton             = new JButton("Withdraw");
  private JButton depositButton              = new JButton("Deposit");

  String[] accountColumns = { "ID", "Account Type", "Balance", "Interest" };
  String[] transactionColumns = { "Date", "Time", "Amount", "Balance" };
  String testdata[][] = { { "101", "Amit", "670000" }, { "102", "Jai", "780000" }, { "101", "Sachin", "700000" } };

  public GUImain() {
    initiateInstanceVariables();
    buildFrame();
  }

  private void initiateInstanceVariables() {
    logic = new BankLogic();

    customerList = new JList<Object>();

    accountTable = new JTable();
    DefaultTableModel model = new DefaultTableModel(0, 0);
    model.setColumnIdentifiers(accountColumns);
    accountTable.setModel(model);

    transactionTable = new JTable();
    DefaultTableModel model1 = new DefaultTableModel(0, 0);
    model1.setColumnIdentifiers(transactionColumns);
    transactionTable.setModel(model1);
    model.addRow(new String[] {"data", "data","data", "data"});

    nameField = new JTextField();
    lastnameField = new JTextField();
    pNrField = new JTextField();


    nameField.setBorder(BorderFactory.createTitledBorder("Name"));
    lastnameField.setBorder(BorderFactory.createTitledBorder("Lastname"));
    pNrField.setBorder(BorderFactory.createTitledBorder("pNr"));

  }

  private void buildFrame() {
    setTitle("Bank");
    setSize(300, 250);
    setLayout(new GridLayout(1, 2));

    JPanel bankpanel = new JPanel(new GridLayout(5, 1));
    bankpanel.add(nameField);
    bankpanel.add(lastnameField);
    bankpanel.add(pNrField);
    bankpanel.add(addButton);
    bankpanel.add(showButton);
    bankpanel.add(clearButton);
    bankpanel.add(createSavingsAccountButton);
    bankpanel.add(createCreditAccountButton);

    createSavingsAccountButton.setVisible(false);
    createCreditAccountButton.setVisible(false);

    addButton.addActionListener(this);
    showButton.addActionListener(this);
    clearButton.addActionListener(this);
    createSavingsAccountButton.addActionListener(this);
    createCreditAccountButton.addActionListener(this);
    deleteAccountButton.addActionListener(this);

//    // ACCOUNT TABLE
    accountTable.setCellSelectionEnabled(true);
    ListSelectionModel select = accountTable.getSelectionModel();
    select.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
//    // ACCOUNT TABLE

    add(bankpanel);
    add(customerList);
    add(new JScrollPane(accountTable), BorderLayout.CENTER);
    add(new JScrollPane(transactionTable), BorderLayout.CENTER);

    setDefaultCloseOperation(EXIT_ON_CLOSE);

  }

  // UI LOGIC. This activated the functions below.
  public void actionPerformed(ActionEvent event) {
    String buttonText = event.getActionCommand();
    if (buttonText.equals("Add Customer")) {
      addCustomer();
      showAccountButtons();
    }
    if (buttonText.equals("Show")) {
      showSelected();
    }
    if (buttonText.equals("Clear")) {
      clear();
    }
    if (buttonText.equals("Create Savings Account")) {
      createSavingsAccount();

    }
    if (buttonText.equals("Create Credit Account")) {
      createCreditAccount();
    }
  }

  private void addCustomer() {
    logic.createCustomer(nameField.getText(), lastnameField.getText(), pNrField.getText());
    customerList.setListData(logic.getAllCustomers().toArray());
    clear();
  }

  public void createCreditAccount() {
    logic.createCreditAccount(pNrField.getText());
    model.addRow(new String[] {"data", "data","data", "data"});
  }

  public void createSavingsAccount() {
    logic.createSavingsAccount(pNrField.getText());
    model.addRow(new String[] {"data", "data","data", "data"});
  }

  private void showSelected() {
    int position = customerList.getSelectedIndex();
    if (position > -1) {
      nameField.setText(logic.getNameForPersonAt(position));
      lastnameField.setText(logic.getLastNameForPersonAt(position));
      pNrField.setText(logic.getpNrAt(position));
    } else {
      JOptionPane.showMessageDialog(null, "You need a person in the list!");
    }
  }

  private void showAccountButtons() {
    createSavingsAccountButton.setVisible(true);
    createCreditAccountButton.setVisible(true);
  }

  private void clear() {
    nameField.setText("");
    lastnameField.setText("");
    pNrField.setText("");
  }
}

Answer 1

你有＆＃34;阴影变量＆＃34;。

您尝试定义实例变量，但它们为null：

private DefaultTableModel model;
private DefaultTableModel model1;

然后创建一个非空的局部变量

DefaultTableModel model = new DefaultTableModel(0, 0);
...
DefaultTableModel model1 = new DefaultTableModel(0, 0);

ActionListener只能访问实例变量，但它为null，因此您获得了NPE。

摆脱局部变量：

model = new DefaultTableModel(0, 0);
...
model1 = new DefaultTableModel(0, 0);

JTable addRow不适用于actionListner

1 个答案: