在两个jframe之间交换变量

Question

我有三个java文件。DBConn -这个类连接到数据库并执行查询。

UserLogin -这个jFrame将获取用户名和密码，并与"users"表进行比较如果匹配，它将在LibSysMain java文件

中显示"Login Successfull"

LibSysMain -这是显示菜单的主文件。这是应用程序运行时首先显示的jFrame。

问题是我无法在LibSysMain中设置"登录成功"消息。

我的数据库是MS Access。表名称为"users"。字段为"用户名"one_answers"密码"。它们都是字符串类型

如果你能帮助我，我将不胜感激。

我是Java新手。我使用的是NetBeans 6.9.1。以下是列表:

DBConn:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package LibSystem;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.ResultSet;
import javax.swing.JOptionPane;
/**
 *
 * @author Administrator
 */
public class DBConn {
    Connection con;
    Statement stmt;
    ResultSet rs;

    public void DoConnect(String querydb)
    {
        String SQL;
        SQL=querydb;
        try
        {
            // CONNECT TO THE DATABASE
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
            String url = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb, *.accdb)};DBQ=C:\Database\libsys\libsys.mdb";
            con = DriverManager.getConnection(url);
            System.out.println("nConnected to the database");
            //QUERY THE DATABASE
            stmt = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
            //String SQL ="Select * from Members";
            rs=stmt.executeQuery(SQL);
            //MOVE CURSOR AT FIRST RECORD AND FETCH DATA
            rs.next();
        }
        catch(ClassNotFoundException e)
        {
             System.out.println("nClass not found. Check Path");
             e.printStackTrace();
        }
        catch (SQLException err)
        {
            JOptionPane.showMessageDialog(null, err.getMessage());
        }
    }
}

UserLogin:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
/*
 * UserLogin.java
 *
 * Created on Apr 23, 2011, 8:46:59 PM
 */
package LibSystem;
import java.sql.*;
import javax.swing.JOptionPane;
import java.lang.*;

/**
 *
 * @author Administrator
 */
public class UserLogin extends javax.swing.JFrame {
    private String user;
    private String password;
    private String status;
    /** Creates new form UserLogin */
    public UserLogin() {
        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() {
        txtUserName = new javax.swing.JTextField();
        txtPassword = new javax.swing.JTextField();
        btnClose = new javax.swing.JButton();
        btnLogin = new javax.swing.JButton();
        lbUserName = new javax.swing.JLabel();
        lbPassword = new javax.swing.JLabel();
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        btnClose.setText("Close");
        btnClose.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnCloseActionPerformed(evt);
            }
        });
        btnLogin.setText("Login");
        btnLogin.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnLoginActionPerformed(evt);
            }
        });
        lbUserName.setText("User Name");
        lbPassword.setText("Password");
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(34, 34, 34)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(lbPassword)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 134, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                        .addGroup(layout.createSequentialGroup()
                            .addComponent(lbUserName)
                            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 128, javax.swing.GroupLayout.PREFERRED_SIZE))
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addGroup(layout.createSequentialGroup()
                                .addComponent(btnClose)
                                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 64, Short.MAX_VALUE)
                                .addComponent(btnLogin))
                            .addComponent(txtUserName, javax.swing.GroupLayout.PREFERRED_SIZE, 180, javax.swing.GroupLayout.PREFERRED_SIZE)
                            .addComponent(txtPassword, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, 180, Short.MAX_VALUE))))
                .addGap(35, 35, 35))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(26, 26, 26)
                .addComponent(lbUserName)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(txtUserName, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(lbPassword)
                .addGap(5, 5, 5)
                .addComponent(txtPassword, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(btnClose)
                    .addComponent(btnLogin))
                .addContainerGap(39, Short.MAX_VALUE))
        );
        pack();
    }// </editor-fold>                        
    private void btnLoginActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        //CREATE AN INSTANCE OF DBCONN CLASS TO CONNECT TO THE DATABASE
        //WE TAKE THE USERNAME FROM THE LOGIN WINDOW AND SEARCH THE USER
        //BASED ON THAT USER. IF FOUND, COMPARE IT WITH THE LOGIN WINDOW.
        //IF NOT FOUND DISPLAY ERROR MESSAGE.
        DBConn dbc = new DBConn();
        String qry = "Select * from users where username=" + "'" + txtUserName.getText() + "'";
        dbc.DoConnect(qry);
        try
        {
            setUsername(dbc.rs.getString("username"));
            setPassword(dbc.rs.getString("password"));
            //TEST PRINTOUT OF USERNAME AND PASSWORD FOR DEBUGGING
            System.out.println(getUsername());
            System.out.println(getPassword());
           if (user.equals(txtUserName.getText()) && password.equals(txtPassword.getText()))
            {
                JOptionPane.showMessageDialog(UserLogin.this, "Login Successfull");
                this.setStatus("pass");
                dispose();
            }
            else
            {
               JOptionPane.showMessageDialog(UserLogin.this, "Login unsuccessful");
               setStatus("fail");
            }

        }
        catch  (SQLException err)
        {
               JOptionPane.showMessageDialog(UserLogin.this, err.getMessage());
        }
    }                                        
    private void btnCloseActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
           this.dispose();
    }                                        
    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new UserLogin().setVisible(true);
            }
        });
    }
    public void setUsername(String u)
    {
        user = u;
    }
     public void setPassword(String p)
    {
        password = p;
    }

    public String getUsername()
    {
        return user;
    }
     public String getPassword()
    {
        return password;
    }
     public void setStatus(String stat)
    {
        status = stat;
    }
     public String getStatus()
    {
        return status;
    }
    // Variables declaration - do not modify                     
    private javax.swing.JButton btnClose;
    private javax.swing.JButton btnLogin;
    private javax.swing.JLabel lbPassword;
    private javax.swing.JLabel lbUserName;
    private javax.swing.JTextField txtPassword;
    private javax.swing.JTextField txtUserName;
    // End of variables declaration                   
}

LibSysMain:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
/*
 * LibsysMain.java
 *
 * Created on Apr 23, 2011, 6:48:18 PM
 */
package LibSystem;
import javax.swing.JOptionPane;
/**
 *
 * @author Administrator
 */
public class LibsysMain extends javax.swing.JFrame {
   String q;
    /** Creates new form LibsysMain */
    public LibsysMain()
    {
        initComponents();
        //DBConn dbc = new DBConn();
        //q="Select * from users";
        //dbc.DoConnect(q);
    }
//        LibsysMain frame1 = new LibsysMain();
//        UserLogin frame2 = new UserLogin(frame1);
    /** 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() {
        jPanel2 = new javax.swing.JPanel();
        jPanel1 = new javax.swing.JPanel();
        jPanel3 = new javax.swing.JPanel();
        jLabel1 = new javax.swing.JLabel();
        jSeparator1 = new javax.swing.JSeparator();
        jMenuBar1 = new javax.swing.JMenuBar();
        miLogin = new javax.swing.JMenu();
        jMenuItem1 = new javax.swing.JMenuItem();
        jMenuItem2 = new javax.swing.JMenuItem();
        javax.swing.GroupLayout jPanel2Layout = new javax.swing.GroupLayout(jPanel2);
        jPanel2.setLayout(jPanel2Layout);
        jPanel2Layout.setHorizontalGroup(
            jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 100, Short.MAX_VALUE)
        );
        jPanel2Layout.setVerticalGroup(
            jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 100, Short.MAX_VALUE)
        );
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowActivated(java.awt.event.WindowEvent evt) {
                formWindowActivated(evt);
            }
        });
        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 539, Short.MAX_VALUE)
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 328, Short.MAX_VALUE)
        );
        jLabel1.setText("Status");
        javax.swing.GroupLayout jPanel3Layout = new javax.swing.GroupLayout(jPanel3);
        jPanel3.setLayout(jPanel3Layout);
        jPanel3Layout.setHorizontalGroup(
            jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel3Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jLabel1)
                .addContainerGap(518, Short.MAX_VALUE))
        );
        jPanel3Layout.setVerticalGroup(
            jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jLabel1, javax.swing.GroupLayout.DEFAULT_SIZE, 25, Short.MAX_VALUE)
        );
        jSeparator1.setAlignmentX(0.0F);
        jSeparator1.setMinimumSize(new java.awt.Dimension(10, 10));
        miLogin.setText("Connect");
        miLogin.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                miLoginActionPerformed(evt);
            }
        });
        jMenuItem1.setText("Login");
        jMenuItem1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jMenuItem1ActionPerformed(evt);
            }
        });
        miLogin.add(jMenuItem1);
        jMenuItem2.setText("Exit");
        jMenuItem2.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jMenuItem2ActionPerformed(evt);
            }
        });
        miLogin.add(jMenuItem2);
        jMenuBar1.add(miLogin);
        setJMenuBar(jMenuBar1);
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel3, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addComponent(jSeparator1, javax.swing.GroupLayout.DEFAULT_SIZE, 559, Short.MAX_VALUE)
            .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)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(jSeparator1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(4, 4, 4)
                .addComponent(jPanel3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
        );
        pack();
    }// </editor-fold>                        
    private void miLoginActionPerformed(java.awt.event.ActionEvent evt) {                                        
        // TODO add your handling code here:
    }                                       
    private void jMenuItem1ActionPerformed(java.awt.event.ActionEvent evt) {                                           
        // TODO add your handling code here:
        UserLogin ul = new UserLogin();
        ul.setVisible(true);
        //SET THE STATUS IF LOGIN IS SUCCESSFULL
        if (ul.getStatus() == "pass")
        {
            jLabel1.setText("Logged In");
        }
        else
        {
            jLabel1.setText("Cannot Log in");
        }
    }                                          
    private void jMenuItem2ActionPerformed(java.awt.event.ActionEvent evt) {                                           
        // TODO add your handling code here:
        System.exit(0);
    }                                          
    private void formWindowActivated(java.awt.event.WindowEvent evt) {                                     
        // TODO add your handling code here:
    }                                    
    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new LibsysMain().setVisible(true);
            }
        });
    }
    // Variables declaration - do not modify                     
    private javax.swing.JLabel jLabel1;
    private javax.swing.JMenuBar jMenuBar1;
    private javax.swing.JMenuItem jMenuItem1;
    private javax.swing.JMenuItem jMenuItem2;
    private javax.swing.JPanel jPanel1;
    private javax.swing.JPanel jPanel2;
    private javax.swing.JPanel jPanel3;
    private javax.swing.JSeparator jSeparator1;
    private javax.swing.JMenu miLogin;
    // End of variables declaration                   
}

Answer 1

我有几个建议:

• 首先，不要像这里if (ul.getStatus() == "pass")那样比较String与==，因为这会检查两个变量是否引用相同的String对象(您不关心)，而是使用equals或equalsIgnoreCase方法来检查两个String是否包含相同的String数据(您确实关心)。例如,如果(ul.getStatus () .equalsIgnoreCase("通过"))
• 确保在GUI线程的线程背景中执行所有数据库查询和其他操作，EDT可以通过使用SwingWorker对象来实现。本文将告诉您我所说的内容，并提供详细信息:Swing中的并发性。
• 考虑使用单个JFrame和模态对话框作为主应用程序的对话窗口。这可以通过使用JOptionPanes或模态jdialog来实现，特别是对于你的UserLogin窗口。
• 出于这个原因，我喜欢把我的GUI转向创建jpanel，而不是像JFrames这样的顶层窗口。通过这种方式，我可以将GUI/JPanel放置到任何类型的窗口中，这取决于情况是JFrame, JApplet, JDialog, JOptionPane，甚至嵌套到另一个JPanel中。这给了你惊人的灵活性。