我有一个登录表程序。我试图获取actionListener方法中的本地用户变量,以便在用户回答问题时在mysql数据库中使用它。所以基本上我有一个类,用户登录,然后它转到另一个表单,点击开始测试,然后它转到我想使用用户变量的表单。我已经做了getter和setter方法来获得用户名,然后在JFrame中使用它,用户回答一个问题。当我在这个类中打印消息时,它返回用户变量。但是当我想在另一个JFrame中使用它时,它返回null!有什么主意,我怎么办?
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JOptionPane;
import javax.swing.JTextField;
import javax.swing.JLabel;
import javax.swing.JButton;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import javax.swing.JPasswordField;
public class Build1 extends JFrame {
private JPanel contentPane;
private JTextField textField;
private JPasswordField passwordField;
private String user;
JFrame frame;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Build1 frame = new Build1();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public Build1() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 500, 500);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
textField = new JTextField();
textField.setBounds(96, 58, 86, 20);
contentPane.add(textField);
textField.setColumns(10);
JLabel lblUsername = new JLabel("Username");
lblUsername.setBounds(10, 61, 59, 14);
contentPane.add(lblUsername);
JLabel lblPassword = new JLabel("Password");
lblPassword.setBounds(10, 113, 59, 14);
contentPane.add(lblPassword);
JButton btnLogin = new JButton("Login");
btnLogin.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
try{
String user = textField.getText().trim();
String pass = String.valueOf(passwordField.getPassword());
setUsername(user);
getUsername();
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/users","root","1234");
PreparedStatement st = con.prepareStatement("select * from user where username='"+user+"'");
ResultSet rs = st.executeQuery();
if(rs.next())
{
String dbpass = rs.getString(4);
if(dbpass.equals(pass)){
if(user.equals("Admin")){
Build5 Admin = new Build5();
Admin.setVisible(true);
Build1.this.dispose();
Build1.this.setVisible(false);
}
else{
JOptionPane.showMessageDialog(frame," "+user);
Build2 User = new Build2();
User.setVisible(true);
Build1.this.dispose();
Build1.this.setVisible(false);
}
}
else
{
JOptionPane.showMessageDialog(null,"Login Unsuccessful!","Error",1);
}
}
else
{
JOptionPane.showMessageDialog(null,"Username not found","Error",1);
}
} catch (SQLException ex) {
System.out.println(ex);
}
}
});
btnLogin.setBounds(186, 202, 89, 23);
contentPane.add(btnLogin);
JButton btnRegister = new JButton("Register");
btnRegister.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
try {
Build3 frame = new Build3();
frame.setVisible(true);
Build1.this.dispose();
Build1.this.setVisible(false);
} catch (Exception e1) {
e1.printStackTrace();
}
}
});
btnRegister.setBounds(186, 236, 89, 23);
contentPane.add(btnRegister);
JButton btnRecoverPassword = new JButton("Recover Password");
btnRecoverPassword.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
try {
Build4 frame = new Build4();
frame.setVisible(true);
Build1.this.dispose();
Build1.this.setVisible(false);
} catch (Exception e1) {
e1.printStackTrace();
}
}
});
btnRecoverPassword.setBounds(153, 270, 147, 23);
contentPane.add(btnRecoverPassword);
passwordField = new JPasswordField();
passwordField.setBounds(96, 110, 86, 20);
contentPane.add(passwordField);
}
public void setUsername(String user){
this.user = this.textField.getText();
}
public String getUsername() {
JOptionPane.showMessageDialog(frame,"1 "+user);
return user;
}
}
另一类:
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Timestamp;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JOptionPane;
import javax.swing.JRadioButton;
import javax.swing.JLabel;
public class Build6 extends JFrame {
private JPanel contentPane;
JFrame frame;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Build6 frame1 = new Build6();
frame1.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public Build6() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 500, 500);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
final JRadioButton rdbtnTrue = new JRadioButton("True");
rdbtnTrue.setBounds(162, 132, 109, 23);
contentPane.add(rdbtnTrue);
final JRadioButton rdbtnFalse = new JRadioButton("False");
rdbtnFalse.setBounds(162, 158, 109, 23);
contentPane.add(rdbtnFalse);
final JRadioButton rdbtnDontKnow = new JRadioButton("Don't know");
rdbtnDontKnow.setBounds(162, 184, 109, 23);
contentPane.add(rdbtnDontKnow);
final JRadioButton rdbtnWhatever = new JRadioButton("Whatever");
rdbtnWhatever.setBounds(162, 210, 109, 23);
contentPane.add(rdbtnWhatever);
JLabel lblDoesAMan = new JLabel("Does a man fly?");
lblDoesAMan.setBounds(162, 97, 109, 14);
contentPane.add(lblDoesAMan);
JButton btnAnswer = new JButton("Answer");
btnAnswer.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
try {
Build1 a = new Build1();
String user = a.getUsername();
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/answers","root","1234");
Connection con1 = DriverManager.getConnection("jdbc:mysql://localhost:3306/users","root","1234");
PreparedStatement st = con1.prepareStatement("select * from user where username='"+user+"'");
ResultSet rs = st.executeQuery();
while(rs.next()){
String username = rs.getString("username");
if(user.equals(username)){
JOptionPane.showMessageDialog(frame,"DAN DAN!"+user+" "+username);
}
}
if(rdbtnDontKnow.isSelected()){
java.util.Date dt = new java.util.Date();
java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
java.text.SimpleDateFormat sdf1 = new java.text.SimpleDateFormat("yyyy-MM-dd");
String currentday = sdf1.format(dt);
String currentdayTime = sdf.format(dt);
String answer = "Wrong";
String test ="test1";
PreparedStatement st11 = (PreparedStatement) con.prepareStatement("INSERT INTO answer (username,daytime,answer,test,day) VALUES (?,?,?,?,?)");
st11.setString(1, user);
st11.setString(2, currentdayTime);
st11.setString(3, answer);
st11.setString(4, test);
st11.setString(5, currentday);
st11.executeUpdate();
st11.close();
}
else if(rdbtnWhatever.isSelected()){
java.util.Date dt = new java.util.Date();
java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
java.text.SimpleDateFormat sdf1 = new java.text.SimpleDateFormat("yyyy-MM-dd");
String currentdayTime = sdf.format(dt);
String currentday = sdf1.format(dt);
String answer = "Wrong";
String test ="test1";
PreparedStatement st11 = (PreparedStatement) con.prepareStatement("INSERT INTO answer (username,daytime,answer,test,day) VALUES (?,?,?,?,?)");
st11.setString(1, user);
st11.setString(2, currentdayTime);
st11.setString(3, answer);
st11.setString(4, test);
st11.setString(5, currentday);
st11.executeUpdate();
st11.close();
}
else if(rdbtnTrue.isSelected()){
java.util.Date dt = new java.util.Date();
java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
java.text.SimpleDateFormat sdf1 = new java.text.SimpleDateFormat("yyyy-MM-dd");
String currentday = sdf1.format(dt);
String currentdayTime = sdf.format(dt);
String answer = "Wrong";
String test ="test1";
PreparedStatement st11 = (PreparedStatement) con.prepareStatement("INSERT INTO answer (username,daytime,answer,test,day) VALUES (?,?,?,?,?)");
st11.setString(1, user);
st11.setString(2, currentdayTime);
st11.setString(3, answer);
st11.setString(4, test);
st11.setString(5, currentday);
st11.executeUpdate();
st11.close();
}
else if(rdbtnFalse.isSelected()){
java.util.Date dt = new java.util.Date();
java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
java.text.SimpleDateFormat sdf1 = new java.text.SimpleDateFormat("yyyy-MM-dd");
String currentday = sdf1.format(dt);
String currentdayTime = sdf.format(dt);
String answer = "Wrong";
String test ="test1";
PreparedStatement st11 = (PreparedStatement) con.prepareStatement("INSERT INTO answer (username,daytime,answer,test,day) VALUES (?,?,?,?,?)");
st11.setString(1, user);
st11.setString(2, currentdayTime);
st11.setString(3, answer);
st11.setString(4, test);
st11.setString(5, currentday);
st11.executeUpdate();
st11.close();
}else{
JOptionPane.showMessageDialog(frame,"Select an answer!");
}
} catch (Exception e1) {
e1.printStackTrace();
}
}
});
btnAnswer.setBounds(192, 261, 89, 23);
contentPane.add(btnAnswer);
ButtonGroup group = new ButtonGroup(); //Σε περίπτωση που θέλουμε να διαλέγει μόνο ένα!
group.add(rdbtnTrue);
group.add(rdbtnFalse);
group.add(rdbtnDontKnow);
group.add(rdbtnWhatever);
}
}
编辑(20/1):新的登录表单(用户变量所在的sql部分)
JButton lgnBtn = new JButton("Login");
lgnBtn.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
try{
String user = t.getText().trim();
String pass = String.valueOf(t1.getPassword());
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/users","root","1234");
PreparedStatement st = con.prepareStatement("select * from user where username='"+user+"'");
ResultSet rs = st.executeQuery();
if(rs.next())
{
String dbpass = rs.getString(4);
if(dbpass.equals(pass)){
if(user.equals("Admin")){
Build5 Admin = new Build5();
Admin.setVisible(true);
}
else{
JOptionPane.showMessageDialog(frame," "+user);
Build2 User = new Build2();
User.setVisible(true);
}
}
else
{
JOptionPane.showMessageDialog(null,"Login Unsuccessful!","Error",1);
}
}
else
{
JOptionPane.showMessageDialog(null,"Username not found","Error",1);
}
} catch (SQLException ex) {
System.out.println(ex);
}
}
});
最佳答案
建议:
您的登录窗口不应该是JFrame,而应该是一个模式对话框,如JOptionPane或模式JDialog。这样,当调用代码显示对话框时,调用代码中的所有代码流都将停止,并保持停止状态,直到对话框不再可见为止。
一旦对话框不再可见并且调用代码恢复,就可以查询对话框类的状态并获取登录信息。
你没有告诉我们(或者我没有看到)你如何从其他地方调用这个代码。这是关键,因为这是你的问题所在,这是我们必须看到的。
正如克利奥帕特拉所说,不要使用空布局和组件的直接定位和大小调整,因为它会回来咬你的牙,相信我。
编辑
是的,我相信你的问题正如我所预测的那样,是因为你正在使用JFrame作为一个对话框窗口。看这里:
Build1 a = new Build1();
String user = a.getUsername();
由于Build1是一个非模态JFrame,所以当它被设置为可见时,它不会阻塞调用代码。因此,在用户有机会将数据输入Build1窗口之前,会立即调用
a.getUsername()
。一种解决方案是使用一个WindowListener来查看Build1窗口何时不再可见,但为什么要经历这种混乱。相反,为什么不简单地使用模式JDialog而不是JFrame作为对话框窗口。
同样,你会想停止使用空布局和绝对定位,相信我。它会咬你的。
编辑2
你说:
首先,你能给我举个JDialog的例子吗?
创建和使用JDialog类似于创建JFrame,只是您应该在构造函数中传入对父窗口的引用,并告诉它是否是模态的。请查看JDialog API以了解其构造函数的详细信息。另外,我已经在这个网站上写了很多使用这个的例子,我邀请你在我的名字和JDialog这个词上搜索一下这个网站,你会发现我写的很多例子。另外,我建议您将大部分的GUI创建都放在JPanel的创建上,然后您可以在需要的地方轻松地放置这些JPanel:JFrame、modal JDialog、JOptionPane、另一个JPanel,。。。它给你的GUI提供了很大的灵活性。
第二个空布局您的意思是:contentPane.setLayout(null)?
对。
为什么我要停止使用它们?我的代码会有问题吗?
你的图形用户界面将非常“僵化”,虽然它在你的系统上看起来不错,但在其他平台上,甚至在类似的平台上,可能看起来不太好,但屏幕分辨率不同。不仅如此,你的GUI很难改变、更新或改进。例如,请查看StackOverflow答案here中的代码。代码创建一个JPanel,该JPanel使用GridBagLayout显示jlabel和JTextFields的网格,显示如下:
在该代码中,我使用一个简单的字符串数组指定jlabel:
String[] labelTexts = new String[] { "Width of Frame:",
"Height of Frame:", "# OF Balls:", "Color:" };
正如我在回答中所说,这段代码的美妙之处在于,如果您希望添加另一个字段,比如说一个线条粗细字段,并希望将其添加到倒数第二个字段,那么代码所需的唯一更改就是更改此字段:
String[] labelTexts = new String[] { "Width of Frame:",
"Height of Frame:", "# OF Balls:", "Color:" };
对此:
String[] labelTexts = new String[] { "Width of Frame:",
"Height of Frame:", "# OF Balls:", "Line Thickness:", "Color:" };
结果是:
这是唯一可能的,因为我使用布局管理器来帮助我生成GUI。如果是手工操作,则必须定位新组件,但还必须手动重新定位添加的任何新组件的右侧和下方的所有组件。如果对GUI进行重大更改,这可能会很麻烦,而且很容易出错。相反,这里的布局经理将为您做所有的繁重工作。
还要注意,这段代码是一个使用GUI创建JPanel的示例,我将它显示在JOptionPane(一种模式对话框的形式)中,并且这实际上可以很好地为您工作。
关于java - 将JFrame与变量连接,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/21218525/