我有一个简单的登录表单，该表单可以编译并且不显示任何编译或生成错误，但是在我尝试运行它时不显示界面。我已经检查并设置了“ setVisible（true）”，但还是没有运气。 我不确定问题出在哪里，但是任何帮助将不胜感激。我正在使用Netbeans IDE。 这是源代码。
package client.system;
import java.awt.HeadlessException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.swing.JOptionPane;
public class LoginForm extends javax.swing.JPanel {
Connection con = null;
PreparedStatement pst = null;
ResultSet rs = null;
/**
* Creates new form LoginForm
*/
public LoginForm() {
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();
jLabel1 = new javax.swing.JLabel();
jLabel2 = new javax.swing.JLabel();
username = new javax.swing.JTextField();
jLabel3 = new javax.swing.JLabel();
password = new javax.swing.JPasswordField();
login = new javax.swing.JButton();
jLabel1.setFont(new java.awt.Font("Tahoma", 1, 20)); // NOI18N
jLabel1.setText("Log In");
jLabel2.setLabelFor(username);
jLabel2.setText("Username:");
username.setText("Username");
jLabel3.setLabelFor(password);
jLabel3.setText("Password:");
password.setText("Password");
login.setFont(new java.awt.Font("Tahoma", 0, 20)); // NOI18N
login.setText("Login");
login.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
loginActionPerformed(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(50, 50, 50)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jLabel1, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGroup(jPanel1Layout.createSequentialGroup()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
.addComponent(password, javax.swing.GroupLayout.DEFAULT_SIZE, 283, Short.MAX_VALUE)
.addComponent(jLabel2, javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(username))
.addContainerGap())
.addGroup(jPanel1Layout.createSequentialGroup()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(login, javax.swing.GroupLayout.PREFERRED_SIZE, 283, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel3))
.addGap(0, 43, Short.MAX_VALUE))))
);
jPanel1Layout.setVerticalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addContainerGap()
.addComponent(jLabel1)
.addGap(18, 18, 18)
.addComponent(jLabel2)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(username, javax.swing.GroupLayout.PREFERRED_SIZE, 34, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jLabel3)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(password, javax.swing.GroupLayout.PREFERRED_SIZE, 34, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(login, javax.swing.GroupLayout.PREFERRED_SIZE, 40, javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap(70, Short.MAX_VALUE))
);
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
this.setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addContainerGap())
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
);
}// </editor-fold>
private void loginActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
String sql="select * from login where username=? and password=?";
try{
con = DriverManager.getConnection("jdbc:mysql://localhost/testsql","root","mysql");
pst = con.prepareStatement(sql);
pst.setString(1, username.getText());
pst.setString(2,password.getText());
rs = pst.executeQuery();
if(rs.next()){
JOptionPane.showMessageDialog(null,"username and password matched");
}else{
JOptionPane.showMessageDialog(null, "Incorrect Username or Password");
}
}catch(SQLException | HeadlessException ex){
JOptionPane.showMessageDialog(null,ex);
}
}
public static void main(String args[]){
java.awt.EventQueue.invokeLater(new Runnable(){
public void run(){
new LoginForm().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JPanel jPanel1;
private javax.swing.JButton login;
private javax.swing.JPasswordField password;
private javax.swing.JTextField username;
// End of variables declaration
}
答案 0 :(得分：1)
创建一个新的JFrame表单。将JPanel表单从项目窗口拖到新创建的JFrame表单上。您必须这样做，因为JPanel要求JFrame根父级在屏幕上可见。它没有任何窗口逻辑。
创建一个新的JFrame并将表单/ JPanel作为子项添加到其中。这是一个非常简单的示例，说明了如何实现此目标：
public class ExampleFrame extends JFrame {
public ExampleFrame() {
MyPanel panel = new MyPanel();
getContentPane().add(panel);
setTitle("My Cool Custom Panel");
setSize(300, 200);
setLocationRelativeTo(null);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
public static void main(String[] args) {
new ExampleFrame().setVisible(true);
}
}