空指针错误 [英] null pointer error
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问题描述
我一个在我的应用程序，其中从数据库中翻出密码，然后一个方法将进入 arraylist1 有登录窗口。此外密码放在用户被放入 arraylist2 然后我检查 arraylist1 包含 arraylist2 ，如果是，那么他们可以如果不继续，那么系统会打印的密码是错误的。不幸的是我不断收到空指针错误
I a have login window in my application, where a method which pulls out password from database and then puts into arraylist1. Also passwords put in by user are put into an arraylist2 and then I check if arraylist1 contains arraylist2 and if yes,then they can proceed if not, then system prints a message that password is wrong. Unfortunately I keep getting null pointer error
请检查我的code：
Model.java
public class Model {
public ArrayList<LogPass> getPass() throws SQLException{
Connection con =null;
PreparedStatement stmt = null;
ResultSet rs = null;
ArrayList<LogPass> list = new ArrayList<LogPass>();
try{
con = DriverManager.getConnection("jdbc:mysql://localhost:3306/xxxxx?user=bbbbb&password=aaaaaa");
stmt = con.prepareStatement("SELECT Pass FROM Logpass");
rs = stmt.executeQuery();
while(rs.next()){
LogPass t = new LogPass();
t.setPass(rs.getString("Pass"));
list.add(t);
}
}
finally{
if(rs != null) try {rs.close();}catch (SQLException se){}
if (stmt != null) try{stmt.close();} catch (SQLException se){}
if (con != null) try {con.close();}catch (SQLException se){}
}
return list;
}
}
Login.java
public class Login extends javax.swing.JFrame {
Control c = new Control();
Model m;
/**
* Creates new form Login
*/
public Login() {
initComponents();
}
/**
* 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() {
jPanel1 = new javax.swing.JPanel();
jComboBox1 = new javax.swing.JComboBox();
jTextField1 = new javax.swing.JTextField();
jPasswordField1 = new javax.swing.JPasswordField();
jLabel1 = new javax.swing.JLabel();
jLabel2 = new javax.swing.JLabel();
jLabel3 = new javax.swing.JLabel();
jButton1 = new javax.swing.JButton();
jButton2 = new javax.swing.JButton();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
jComboBox1.setMaximumRowCount(2);
jComboBox1.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Staff", "Manager", " " }));
jLabel1.setText("Username");
jLabel2.setText("Password");
jLabel3.setText("Domain");
jButton1.setText("Login");
jButton1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton1ActionPerformed(evt);
}
});
jButton2.setText("Exit");
jButton2.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton2ActionPerformed(evt);
}
});
javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
jPanel1.setLayout(jPanel1Layout);
jPanel1Layout.setHorizontalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(62, 62, 62)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
.addComponent(jButton1)
.addGap(37, 37, 37)
.addComponent(jButton2))
.addGroup(jPanel1Layout.createSequentialGroup()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jLabel2)
.addComponent(jLabel3)
.addComponent(jLabel1))
.addGap(34, 34, 34)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
.addComponent(jPasswordField1)
.addComponent(jTextField1)
.addComponent(jComboBox1, 0, 120, Short.MAX_VALUE))))
.addContainerGap(103, Short.MAX_VALUE))
);
jPanel1Layout.linkSize(javax.swing.SwingConstants.HORIZONTAL, new java.awt.Component[] {jLabel1, jLabel2, jLabel3});
jPanel1Layout.linkSize(javax.swing.SwingConstants.HORIZONTAL, new java.awt.Component[] {jButton1, jButton2});
jPanel1Layout.setVerticalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
.addGap(42, 42, 42)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel1)
.addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addComponent(jLabel2)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(jLabel3)
.addGap(0, 0, Short.MAX_VALUE))
.addGroup(jPanel1Layout.createSequentialGroup()
.addComponent(jPasswordField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jComboBox1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 41, Short.MAX_VALUE)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jButton2)
.addComponent(jButton1))
.addGap(29, 29, 29))))
);
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
);
pack();
}// </editor-fold>
private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
System.exit(0);
}
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
//try {
// TODO add your handling code here:
//String a = new String(jPasswordField1.getPassword());
// ArrayList<LoginPass2> list2 = new ArrayList<LoginPass2>();
//LoginPass2 l = new LoginPass2();
//l.setPass2(a);
//list2.add(l);
//if(m.getPass().equals(l)){
// if(m.getPass().containsAll(list2)){
this.setVisible(false);
c.setVisible(true);
//}//else{System.out.println("Wrong username or password!");}
//} catch (SQLException ex) {
// Logger.getLogger(Login.class.getName()).log(Level.SEVERE, null, ex);
//}
}
/**
* @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(Login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(Login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(Login.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(Login.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 Login().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JButton jButton1;
private javax.swing.JButton jButton2;
private javax.swing.JComboBox jComboBox1;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JPanel jPanel1;
private javax.swing.JPasswordField jPasswordField1;
private javax.swing.JTextField jTextField1;
// End of variables declaration
}
LogPass.java
public class LogPass {
private String log;
private String pass;
public String getLog(){
return log;
}
public void setLog(String l){
log = l ;
}
public String getPass(){
return pass;
}
public void setPass(String p){
pass = p ;
}
}
LoginPass2.java
public class LoginPass2 {
private String log;
private String pass;
public String getLog2(){
return log;
}
public void setLog2(String l){
log = l ;
}
public String getPass2(){
return pass;
}
public void setPass2(String p){
pass = p ;
}
}
这是错误消息我得到
and this is the error message i get
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at fish.Login.jButton1ActionPerformed(Login.java:152)
at fish.Login.access$000(Login.java:14)
at fish.Login$1.actionPerformed(Login.java:59)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2713)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:680)
at java.awt.EventQueue$4.run(EventQueue.java:678)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:677)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
感谢您的帮助：）
thanks for your help:)
推荐答案
你在哪里得到空指针错误？
Where are you getting the NULL pointer error?
您应该错误检查变量 CON ，语句和 RS 他们的任务后。另外，你的，而循环似乎是错误的。首先，它似乎并没有通过一套移动。另外，你确定条件返回真正？
You should error check for the variables con , stmt and rs after their assignments. Also , your while loop seems to be wrong. First, it does not seem to be moving through the set. Also, are you sure the condition returns true?
这篇关于空指针错误的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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