我在Netbeans 7.2.1中创建了一个基本的Java程序。这是我的注册页面，用户在其中注册帐户。我使用＆＃34;卷轴＆＃34;从我的数据库访问信息的属性。但是，它一直给我这个错误（仅在运行时，而不是在编译时）：
run:
[EL Info]: 2013-11-07 15:05:22.977--ServerSession(751265673)--EclipseLink, version: Eclipse Persistence Services - 2.3.2.v20111125-r10461
[EL Info]: 2013-11-07 15:05:23.721--ServerSession(751265673)--file:/C:/Users/Christiaan/Documents/Skoolwerk/11A1/IT/PAT/PAT 3/build/classes/_TryNCatchDBPU login successful
Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: Cannot cast java.lang.String to java.util.List
at java.lang.Class.cast(Class.java:3005)
at org.jdesktop.beansbinding.Binding.convertForward(Binding.java:1312)
at org.jdesktop.beansbinding.Binding.getSourceValueForTarget(Binding.java:844)
at org.jdesktop.beansbinding.Binding.refreshUnmanaged(Binding.java:1222)
at org.jdesktop.beansbinding.Binding.refresh(Binding.java:1207)
at org.jdesktop.beansbinding.Binding.refreshAndNotify(Binding.java:1143)
at org.jdesktop.beansbinding.AutoBinding.sourceChangedImpl(AutoBinding.java:223)
at org.jdesktop.beansbinding.Binding.sourceChanged(Binding.java:1411)
at org.jdesktop.beansbinding.Binding.access$1200(Binding.java:38)
at org.jdesktop.beansbinding.Binding$PSL.propertyStateChanged(Binding.java:1618)
at org.jdesktop.beansbinding.PropertyHelper.firePropertyStateChange(PropertyHelper.java:212)
at org.jdesktop.beansbinding.ELProperty.notifyListeners(ELProperty.java:688)
at org.jdesktop.beansbinding.ELProperty.access$800(ELProperty.java:155)
at org.jdesktop.beansbinding.ELProperty$SourceEntry.processSourceChanged(ELProperty.java:312)
at org.jdesktop.beansbinding.ELProperty$SourceEntry.sourceChanged(ELProperty.java:326)
at org.jdesktop.beansbinding.ELProperty$SourceEntry.propertyChange(ELProperty.java:333)
at java.beans.PropertyChangeSupport.fire(PropertyChangeSupport.java:335)
at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:327)
at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:263)
at java.awt.Component.firePropertyChange(Component.java:8382)
at pat.pkg3.LoginNewUser.setScroller(LoginNewUser.java:35)
at pat.pkg3.LoginNewUser.<init>(LoginNewUser.java:23)
at pat.pkg3.LoginNewUser$2.run(LoginNewUser.java:229)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:701)
at java.awt.EventQueue.access$000(EventQueue.java:102)
at java.awt.EventQueue$3.run(EventQueue.java:662)
at java.awt.EventQueue$3.run(EventQueue.java:660)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:671)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
BUILD SUCCESSFUL (total time: 5 seconds)
解决错误的唯一方法是删除调用＆＃34; setScroller（）＆＃34;的代码。方法（接近下面代码中的顶部）：
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package pat.pkg3;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
public class LoginNewUser extends javax.swing.JFrame {
JFrame LoginNewUser = new JFrame();
public int size; public String username, password, group;
int index = 0;
public LoginNewUser()
{
initComponents();
setScroller(groupsList.get(index)); //BY REMOVING THIS, IT WORKS
}
private Groups scroller;
public static final String PROP_SCROLLER = "scroller";
public Groups getScroller() {
return scroller;
}
public void setScroller(Groups scroller) {
Groups oldScroller = this.scroller;
this.scroller = scroller;
firePropertyChange(PROP_SCROLLER, oldScroller, scroller);
}
/**
* This method is called from within the constructor to initialize the form.
* WARNING: Do NOT modify this code. The content of this method is always
* regenerated by the Form Editor.
*/
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
bindingGroup = new org.jdesktop.beansbinding.BindingGroup();
TryNCatchDBPUEntityManager = java.beans.Beans.isDesignTime() ? null : javax.persistence.Persistence.createEntityManagerFactory("TryNCatchDBPU").createEntityManager();
groupsQuery = java.beans.Beans.isDesignTime() ? null : TryNCatchDBPUEntityManager.createQuery("SELECT g FROM Groups g");
groupsList = java.beans.Beans.isDesignTime() ? java.util.Collections.emptyList() : groupsQuery.getResultList();
individualQuery = java.beans.Beans.isDesignTime() ? null : TryNCatchDBPUEntityManager.createQuery("SELECT i FROM Individual i");
individualList = java.beans.Beans.isDesignTime() ? java.util.Collections.emptyList() : individualQuery.getResultList();
jlLogo = new javax.swing.JLabel();
jlHeader = new javax.swing.JLabel();
jlEnterUsername = new javax.swing.JLabel();
jlEnterPassword = new javax.swing.JLabel();
jtfUsername = new javax.swing.JTextField();
jbRegister = new javax.swing.JButton();
jlReenterPassword = new javax.swing.JLabel();
jpfPassword = new javax.swing.JPasswordField();
jpfPasswordConfirm = new javax.swing.JPasswordField();
jlChooseGroup = new javax.swing.JLabel();
jcbGroup = new javax.swing.JComboBox();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
jlLogo.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
jlLogo.setIcon(new javax.swing.ImageIcon(getClass().getResource("/pat/pkg3/tryncatch logo.png"))); // NOI18N
jlHeader.setFont(new java.awt.Font("Tahoma", 0, 36)); // NOI18N
jlHeader.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
jlHeader.setText("Register");
jlEnterUsername.setFont(new java.awt.Font("Tahoma", 0, 18)); // NOI18N
jlEnterUsername.setText("Enter a username:");
jlEnterPassword.setFont(new java.awt.Font("Tahoma", 0, 18)); // NOI18N
jlEnterPassword.setText("Enter a password:");
jbRegister.setFont(new java.awt.Font("Tahoma", 0, 24)); // NOI18N
jbRegister.setText("Register");
jbRegister.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jbRegisterActionPerformed(evt);
}
});
jlReenterPassword.setFont(new java.awt.Font("Tahoma", 0, 18)); // NOI18N
jlReenterPassword.setText("Re-enter your password:");
jlChooseGroup.setFont(new java.awt.Font("Tahoma", 0, 18)); // NOI18N
jlChooseGroup.setText("Choose a group:");
org.jdesktop.beansbinding.ELProperty eLProperty = org.jdesktop.beansbinding.ELProperty.create("${scroller.groupname}");
org.jdesktop.swingbinding.JComboBoxBinding jComboBoxBinding = org.jdesktop.swingbinding.SwingBindings.createJComboBoxBinding(org.jdesktop.beansbinding.AutoBinding.UpdateStrategy.READ, this, eLProperty, jcbGroup, "");
bindingGroup.addBinding(jComboBoxBinding);
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addGap(0, 0, Short.MAX_VALUE)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(jbRegister, javax.swing.GroupLayout.PREFERRED_SIZE, 189, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(378, 378, 378))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(jlLogo, javax.swing.GroupLayout.PREFERRED_SIZE, 222, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(359, 359, 359))))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addContainerGap(296, Short.MAX_VALUE)
.addComponent(jlHeader, javax.swing.GroupLayout.PREFERRED_SIZE, 504, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(224, 224, 224))
.addGroup(layout.createSequentialGroup()
.addGap(345, 345, 345)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jlEnterUsername)
.addComponent(jlEnterPassword)
.addComponent(jlReenterPassword)
.addComponent(jlChooseGroup))
.addGap(21, 21, 21)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(jtfUsername, javax.swing.GroupLayout.DEFAULT_SIZE, 180, Short.MAX_VALUE)
.addComponent(jpfPassword)
.addComponent(jpfPasswordConfirm)
.addComponent(jcbGroup, 0, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
.addContainerGap(284, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(jlLogo)
.addGap(11, 11, 11)
.addComponent(jlHeader, javax.swing.GroupLayout.PREFERRED_SIZE, 53, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(18, 18, 18)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(6, 6, 6)
.addComponent(jlEnterUsername))
.addComponent(jtfUsername, javax.swing.GroupLayout.PREFERRED_SIZE, 32, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(28, 28, 28)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jlEnterPassword)
.addComponent(jpfPassword, javax.swing.GroupLayout.PREFERRED_SIZE, 32, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(27, 27, 27)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jlReenterPassword)
.addComponent(jpfPasswordConfirm, javax.swing.GroupLayout.PREFERRED_SIZE, 31, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(24, 24, 24)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jlChooseGroup)
.addComponent(jcbGroup, javax.swing.GroupLayout.PREFERRED_SIZE, 33, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(31, 31, 31)
.addComponent(jbRegister)
.addContainerGap(52, Short.MAX_VALUE))
);
bindingGroup.bind();
java.awt.Dimension screenSize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
setBounds((screenSize.width-1040)/2, (screenSize.height-575)/2, 1040, 575);
}// </editor-fold>
private void jbRegisterActionPerformed(java.awt.event.ActionEvent evt) {
size = individualList.size();
username = jtfUsername.getText();
password = jpfPassword.getText();
String passwordConfirm = jpfPasswordConfirm.getText();
if (!password.equals(passwordConfirm)) //Checks if passwords match
{
JOptionPane.showMessageDialog(null, "Your passwords don't match. Please try again");
}
else{
group = jcbGroup.getSelectedItem().toString();
String sql = "INSERT INTO JAVADB.INDIVIDUAL (NUM, USERNAME, PASSWORD, GROUPNAME, POINTS, COMMUNITYRANKING, GROUPRANKING, NUMPREDICTIONS, NUMCORRECTPREDICTIONS) VALUES (" + (size + 1) + ", " + username + ", " + password + ", " + group + ", 0, 0, 0, 0, 0)";
newUser(sql);
}
}
public void newUser(String sql)
{
try
{
Connection con = DriverManager.getConnection("jdbc:derby://localhost:1527/TryNCatchDB", "javadb", "javadb");
java.sql.Statement st = con.createStatement();
st.executeUpdate(sql);
JOptionPane.showMessageDialog(null, "You have successfully created a new account!");
this.setVisible(false); new Home().setVisible(true); //Opens Home page (Home class)
}
catch(SQLException s)
{
JOptionPane.showMessageDialog(null, "There is already a user with this name. Try again.");
jtfUsername.setText(""); jpfPassword.setText(""); jpfPasswordConfirm.setText(""); //Clears input to try again.
}
}
/**
* @param args the command line arguments
*/
public static void main(String args[]) {
/* Set the Nimbus look and feel */
//<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
/* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
* For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
*/
try {
for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
javax.swing.UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(LoginNewUser.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(LoginNewUser.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(LoginNewUser.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(LoginNewUser.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new LoginNewUser().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.persistence.EntityManager TryNCatchDBPUEntityManager;
private java.util.List<pat.pkg3.Groups> groupsList;
private javax.persistence.Query groupsQuery;
private java.util.List<pat.pkg3.Individual> individualList;
private javax.persistence.Query individualQuery;
private javax.swing.JButton jbRegister;
private javax.swing.JComboBox jcbGroup;
private javax.swing.JLabel jlChooseGroup;
private javax.swing.JLabel jlEnterPassword;
private javax.swing.JLabel jlEnterUsername;
private javax.swing.JLabel jlHeader;
private javax.swing.JLabel jlLogo;
private javax.swing.JLabel jlReenterPassword;
private javax.swing.JPasswordField jpfPassword;
private javax.swing.JPasswordField jpfPasswordConfirm;
private javax.swing.JTextField jtfUsername;
private org.jdesktop.beansbinding.BindingGroup bindingGroup;
// End of variables declaration
}
Here's what the design preview looks like
我面临什么问题？谢谢！