从其他 java 类调用变量 [英] Call variable from other java class

问题描述

我有这个登录屏幕类；

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package program;
import java.sql.*;
import javax.swing.JOptionPane;

/**
 *
 * @author Lacrymae_Ev
 */
public class loginscreen extends javax.swing.JFrame {
    public String username;
    public String getUsername() {
       return username;
    }

    private String pwd;
    public String getPassword() {
       return pwd;
    }

    /**
     * Creates new form loginscreen
     */

    public loginscreen() {
        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() {

        Uname_Textfield = new javax.swing.JTextField();
        Password_PasswordField = new javax.swing.JPasswordField();
        Buton = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setResizable(false);

        Buton.setText("Bağlan");
        Buton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                ButonActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addGap(10, 10, 10)
                        .addComponent(Uname_Textfield, javax.swing.GroupLayout.PREFERRED_SIZE, 150, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(10, 10, 10)
                        .addComponent(Password_PasswordField, javax.swing.GroupLayout.PREFERRED_SIZE, 150, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(54, 54, 54)
                        .addComponent(Buton)))
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(11, 11, 11)
                .addComponent(Uname_Textfield, javax.swing.GroupLayout.PREFERRED_SIZE, 31, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addComponent(Password_PasswordField, javax.swing.GroupLayout.PREFERRED_SIZE, 30, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(Buton, javax.swing.GroupLayout.PREFERRED_SIZE, 31, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );

        pack();
        setLocationRelativeTo(null);
    }// </editor-fold>                        


    private void ButonActionPerformed(java.awt.event.ActionEvent evt) {                                      
        // TODO add your handling code here:
       String username=Uname_Textfield.getText();
       String pwd= new String (Password_PasswordField.getPassword());
    try {  
        Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
        String connectionUrl = "jdbc:sqlserver://192.168.100.100;" + "databaseName=ExampleDB;" + "user=" + username + ";" + "password=" + pwd + ";"; 
        Connection con = DriverManager.getConnection(connectionUrl);
        new ProgramPenceresi().setVisible(true);
        dispose();
        }
    catch (SQLException e) {
            JOptionPane.showMessageDialog(this, "Wrong username or passwordş!");   
        } 
    catch (ClassNotFoundException cE) {
            System.out.println("Class Not Found Exception: "+ cE.toString());
        }
    }                                     


    /**
     * @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(loginscreen.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(loginscreen.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(loginscreen.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(loginscreen.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 loginscreen().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton Buton;
    private javax.swing.JPasswordField Password_PasswordField;
    private javax.swing.JTextField Uname_Textfield;
    // End of variables declaration                   
}

我还有别的课；

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package program;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.swing.JOptionPane;
import net.proteanit.sql.DbUtils;

/**
 *
 * @author Lacrymae_Ev
 */
public class cagbas extends javax.swing.JFrame {
    loginscreen logindetails = new loginscreen ();
    String uname = logindetails.getUsername();
    String pass = logindetails.getPassword();
    private static ResultSet rs;
    private static Statement stmt;
    private static Connection con;
    private static final String query = "select 'AICB',sum(dur) as dur,sum(tot)as tot from exampletable with(nolock)
" +
"where date between '2013-07-01 00:00:00.000' and '2013-07-01 23:59:59.999'
" +
"and id='013'";
    /**
     * Creates new form cagbas
     */
    public cagbas() {
        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() {

        jScrollPane1 = new javax.swing.JScrollPane();
        jTable1 = new javax.swing.JTable();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jTable1.setModel(DbUtils.resultSetToTableModel(rs));
        jScrollPane1.setViewportView(jTable1);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 375, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(15, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 275, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(14, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                        

    /**
     * @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(cagbas.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(cagbas.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(cagbas.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(cagbas.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>
 try
 {     
        Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
        String connectionUrl = "jdbc:sqlserver://192.168.100.100;" + "databaseName=ExampleDB;" + "user=" + uname + ";" + "password=" + pass + ";"; 
        Connection con = DriverManager.getConnection(connectionUrl);
        stmt = con.createStatement();
        rs = stmt.executeQuery(query);
 }
 catch(Exception ex)
 {    
    JOptionPane.showMessageDialog(null, ex.toString());
 } 
        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new cagbas().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTable jTable1;
    // End of variables declaration                   
}

但是我在 cagbas.java 中有问题，因为当我开始这个类时，java 返回以下错误；

But i have problem in cagbas.java because when i start this class java return below error;

我知道我不能在 main 方法中使用非静态 obj.但是如何使用第一个用户在我的程序中输入的真实用户名和密码?

I understand i cant use non-static obj in main method. But how i can use first user entered true username and password in my program ?

推荐答案

我看到的一个问题是你的 LoginScreen 类是一个 JFrame，而 JFrame 的行为是在显示时不停止调用代码的程序流，所以即使您可以在以后的代码中从该对象中提取登录名和密码，您也会过早提取，因为用户还没有时间输入任何内容.

One problem I see is that your LoginScreen class is a JFrame, and a JFrame's behavior is to not stop program flow from the calling code when it is displayed, so even if you could extract the login name and password from this object in your later code, you'll be extracting it too early, before the user has had a time to enter anything.

建议:

• 最重要的是，您正在尝试运行无法编译的代码.永远不要这样做，因为这肯定会失败.相反，在尝试运行您的程序之前修复编译问题.
• 您的 LoginScreen 应该是一个模态 JDialog 而不是一个 JFrame.
• 首先显示此窗口是为了获取用户的输入.
• 这里的关键是，因为它是一个模态 JDialog，所以当显示对话框时调用代码流停止.
• 一旦对话被处理并且不再可见，即一旦用户输入数据或取消对话，调用代码就会恢复.
• 那时，您然后通过调用 getter 方法从 LoginScreen 实例获取登录用户的名称和密码(最好是后者作为 char[] 获取)，并检查以确保它们不为空.即，LoginScreen 应该有一个 public String getUserName() 方法和一个 public char[] getPassword() 方法.
• 调用代码现在可以使用数据库中的此信息.
• 是的，请学习 Java 命名约定，并遵守它们，让您的类名以大写字母开头，方法和变量名以小写字母开头.这将使那些试图理解您的代码并帮助您(即这里的志愿者)做得更好的人更容易.

• Most important is that you're trying to run code that won't compile. Never do this as this is guaranteed to always fail. Instead, fix compilation issues before trying to run your program.
• Your LoginScreen should be a modal JDialog and not a JFrame.
• You first display this window in order to get the user's input.
• Key point here is, that because it is a modal JDialog, the calling code flow stops when the dialog is displayed.
• The calling code then resumes once the dialog has been dealt with and is no longer visible, meaning once the user has either entered data or canceled the dialog.
• At that time, you then get the login user's name and password (best if the latter is obtained as a char[]) from the LoginScreen instance by calling getter methods, and checking to be sure that they are not null. i.e., LoginScreen should have a public String getUserName() method and a public char[] getPassword() method.
• The calling code can now use this information in the database.
• And yeah, please learn Java naming conventions, and please comply with them by having your class names start with upper-case letters and method and variable names with lower-case letters. This will make it easier for folks trying to understand your code and help you, namely the volunteers here, do it better.

编辑

还要注意，JOptionPane 实际上只不过是一个模态 JDialog，这也可以用于您的目的，而且也很容易.例如，在下面的示例代码中，我创建了一个 InputForm JPanel，然后将该 JPanel 放入 JOptionPane:

Note also that a JOptionPane is really nothing more than a modal JDialog, and this can be used for your purposes as well, and easily too. For example, in the example code below I create an InputForm JPanel and then place that JPanel into the JOptionPane:

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;

import javax.swing.*;

@SuppressWarnings("serial")
public class MainFoo extends JPanel {
   private static final int COLUMNS = 10;
   private JTextField userNameField = new JTextField(COLUMNS);
   private JTextField passwordField = new JTextField(COLUMNS);
   private InputForm inputForm = new InputForm();

   public MainFoo() {
      add(new JLabel("User Name:"));
      add(userNameField);
      add(Box.createHorizontalStrut(15));
      add(new JLabel("Password:"));
      add(passwordField);
      add(new JButton(new LogInAction("Log in", KeyEvent.VK_L)));
   }

   private class LogInAction extends AbstractAction {
      public LogInAction(String name, int mnemonic) {
         super(name);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         int result = JOptionPane.showConfirmDialog(null, inputForm, "Input Form",
               JOptionPane.OK_CANCEL_OPTION, JOptionPane.PLAIN_MESSAGE);
         if (result == JOptionPane.OK_OPTION) {
            userNameField.setText(inputForm.getUserName());


            // ***** never do this! ***** 
            // Never change a password into a String.
            // This is for demo purposes only.
            passwordField.setText(new String(inputForm.getPassword())); 
         }
      }
   }

   private static void createAndShowGui() {
      JFrame frame = new JFrame("MainFoo");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new MainFoo());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}


@SuppressWarnings("serial")
class InputForm extends JPanel {
   private static final int COLUMNS = 10;
   private static final int GAP = 3;
   private static final Insets LABEL_INSETS = new Insets(GAP, GAP, GAP, 15);
   private static final Insets TEXTFIELD_INSETS = new Insets(GAP, GAP, GAP, GAP);
   private JTextField userNameField = new JTextField(COLUMNS);
   private JPasswordField passwordField = new JPasswordField(COLUMNS);

   public InputForm() {
      setLayout(new GridBagLayout());
      addLabel("User Name:", 0);
      addTextField(userNameField, 0);

      addLabel("Password:", 1);
      addTextField(passwordField, 1);

   }

   public String getUserName() {
      return userNameField.getText();
   }

   public char[] getPassword() {
      return passwordField.getPassword();
   }


   private void addTextField(JTextField field, int row) {
      GridBagConstraints gbc = new GridBagConstraints();
      gbc.gridwidth = 1;
      gbc.gridheight = 1;
      gbc.gridx = 1;
      gbc.gridy = row;
      gbc.anchor = GridBagConstraints.EAST;
      gbc.fill = GridBagConstraints.HORIZONTAL;
      gbc.insets = TEXTFIELD_INSETS;
      gbc.weightx = 1.0;
      gbc.weighty = 1.0;
      add(field, gbc);
   }

   private void addLabel(String text, int row) {
      GridBagConstraints gbc = new GridBagConstraints();
      gbc.gridwidth = 1;
      gbc.gridheight = 1;
      gbc.gridx = 0;
      gbc.gridy = row;
      gbc.anchor = GridBagConstraints.WEST;
      gbc.fill = GridBagConstraints.BOTH;
      gbc.insets = LABEL_INSETS;
      gbc.weightx = 1.0;
      gbc.weighty = 1.0;
      add(new JLabel(text), gbc);
   }
}

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