我基本上是为一个简单的烘焙程序构建一个简单的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"});
在操作侦听器中不起作用：
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"});
}
如果我尝试创建一个帐户，我会收到以下消息：
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，如果我对将新行添加到表中进行硬编码，(在构造函数中(它可以工作。但我无法动态添加数据。
代码如下：
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("");
}
}
你有"阴影变量"。
您尝试定义实例变量，但它们为空：
private DefaultTableModel model;
private DefaultTableModel model1;
然后你创建一个不为空的局部变量
DefaultTableModel model = new DefaultTableModel(0, 0);
...
DefaultTableModel model1 = new DefaultTableModel(0, 0);
操作侦听器只能访问实例变量，但它为空，因此您可以获得 NPE。
去掉局部变量：
model = new DefaultTableModel(0, 0);
...
model1 = new DefaultTableModel(0, 0);