java将值从jframe传递给另一个jframe并使用它

Question

##这是登录框架的代码##

    public class Login_frame extends javax.swing.JFrame {

  Connection conn = null;
  ResultSet rs = null;
  PreparedStatement pst = null;



public Login_frame() {
    initComponents();
    conn = javaconnect.ConnecrDB();
}


private void cmd_loginActionPerformed(java.awt.event.ActionEvent evt) {                                          
    String sql ="select * from userinfo where username =? and password =? ";
    try{
        pst = conn.prepareStatement(sql);
        pst.setString(1,txt_username.getText());
        pst.setString(2,txt_password.getText());

        rs = pst.executeQuery();

        if(rs.next()){
        JOptionPane.showMessageDialog(null, "Username and Password is correct");
        rs.close();
        pst.close();
       close();
        Welcome_Screen w = new Welcome_Screen();
        w.userName = this.txt_username.getText();
        w.setVisible(true);

        }

}catch(Exception e){

         JOptionPane.showMessageDialog(null, "Invalid username or password");
}finally{
        try{
            rs.close();
            pst.close();


        }catch(Exception e){

        }

    }
}                                         

private void txt_usernameActionPerformed(java.awt.event.ActionEvent evt) {                                             
    // TODO add your handling code here:
}                                            

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
            // TODO add your handling code here:
            this.setVisible(false);
            Register_frame r = new Register_frame();
           r.setVisible(true);

}                                        

public void close(){
    WindowEvent winClosingEvent= new WindowEvent(this,WindowEvent.WINDOW_CLOSING);
    Toolkit.getDefaultToolkit().getSystemEventQueue().postEvent(winClosingEvent);
}    

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

}

这是第二个Jframe的代码

public class Welcome_Screen extends javax.swing.JFrame {
static Object txt_username;
     Connection conn = null;
     ResultSet rs = null;
     PreparedStatement pst = null;
      String username="";
/**     
 * Creates new form Welcome_Screen
 */
public Welcome_Screen() {
    initComponents();
     conn = javaconnect.ConnecrDB();
     Update_table();
      Update_table2();
      update_elements();

}




private void update_elements(){

    try{
      String sql ="select league from Teams where team_owner= '"+username+"' ";
      pst = conn.prepareStatement(sql);
      rs = pst.executeQuery();
            while(rs.next())
            {
             String result =rs.getString("league");
             league_txt.setText(result);

             }


    }catch(Exception e){
    JOptionPane.showMessageDialog(null, e);

    }finally{
        try{
            rs.close();
            pst.close();


        }catch(Exception e){

        }

    }

}

 private void Update_table2(){
    try{

          String sql ="select Player,Pos,Age from user_team ";
          pst = conn.prepareStatement(sql);
          rs = pst.executeQuery();
          myTeam.setModel(DbUtils.resultSetToTableModel(rs));


    }catch(Exception e){
    JOptionPane.showMessageDialog(null, e);

    }finally{
        try{
            rs.close();
            pst.close();


        }catch(Exception e){

        }

    }

}

  private void Update_table(){
    try{

           String sql ="select * from Teams ";
            pst = conn.prepareStatement(sql);
            rs = pst.executeQuery();
            league_table.setModel(DbUtils.resultSetToTableModel(rs));


    }catch(Exception e){
    JOptionPane.showMessageDialog(null, e);

    }finally{
        try{
            rs.close();
            pst.close();


        }catch(Exception e){

        }

    }



}
`I have a problem regarding on how to pass value from one `JFrame` to another and use it to an `sql` query.

让我们更清楚一点。我想制作一个必须JFrame的程序。第一个是登录框架。我想获取用户在用户名文本字段中输入的值，并使用它加载一个表，该表对于每个用户都是唯一的

更简单地说，我想替换这个查询中的userName

String sql ="select league from Teams where team_owner= '"+userName+"' "; 

Answer 1

你不能通过，因为你没有把它存放在任何地方。你也应该 完成此方法正文：

String username;
private void txt_usernameActionPerformed(java.awt.event.ActionEvent evt)     {                                             
    // TODO add your handling code here:
    username = ((JTextField)evt.getSource()).getText();
}  

然后你可以在任何你想要的地方传递用户名

更好的是，您根本不需要使用listener，也不需要在类级别声明txt_用户名。然后，只要调用txt_用户名，就可以随时获得用户输入。getText（）

您的代码看起来是由某个GUI工具生成的。我建议你从手写开始，直到你完全知道生成了什么

第二个答复

看来你改变了密码。我看不到任何组件（）；不再是方法了。我想你需要把它放回去。您声明（或netbeans为您做的）JtextField txt_username=new。。。用那种方法。如果将其移动到LoginFrame类的顶部，即连接和结果集所在的位置，则可以在Login_frame中的任何位置使用它，而不仅仅是在initComponents（）中。顺便说一句，在java中，应该像LoginFrame那样命名类（不要使用underbar，但这只是惯例）

Answer 2

如果有任何困惑，请告诉我。基本上，当你创建一个新的Welcome_Screen实例时，你的构造器如下所示update_elements();被称为。。。然后你的userName在你创建新框架的地方被赋予了它的值。这只是一个订单问题。不过你做的一切都对

String username="";
/**     
 * Creates new form Welcome_Screen
 */
public Welcome_Screen(String userName) {
    initComponents();
     conn = javaconnect.ConnecrDB();
     //this. keyword is very important otherwise the 
     //local variable won't set the frame variable.
     this.userName = userName;
     Update_table();
     Update_table2();
     update_elements();
}

现在，每当使用Welcome_Screen进行new调用时，构造函数上都有一个参数，您需要向它传递一个您选择的字符串。然而，在这一点上，这不是你在这个项目中的选择。你必须这样打电话才能让它工作

//I lied either should be fine.
Welcome_Screen w = new Welcome_Screen(userName);
Welcome_Screen w = new Welcome_Screen(yourTextField.getText());