Question

在我的java项目中，我希望通过输入卷号来查看每个学生的信息。在第一次，我输入卷号，结果来了。但如果我想在同一个窗口看到其他学生的掷骰数，结果就没有了。我的代码中有什么问题？屏幕截图如下：当我更改卷号时，图像和其他信息不会更新。

enter image description here

    public void actionPerformed(ActionEvent e)
    if(e.getSource()==button)
    {

    l1= new JLabel("Name: ");
    l1.setForeground(Color.white);
    l1.setFont(new Font("Serif", Font.BOLD, 15));
    l1.setBounds(100,100,150,20);
    //l1.setLabelFor(tf1);

    l2= new JLabel("Mobile Number: ");
    l2.setForeground(Color.white);
    l2.setFont(new Font("Serif", Font.BOLD, 15));
    l2.setBounds(100,150,150,20);
    //l1.setLabelFor(tf2);

    l3= new JLabel("Father's Name: ");
    l3.setForeground(Color.white);
    l3.setFont(new Font("Serif", Font.BOLD, 15));
    l3.setBounds(100,200,150,20);

    l4= new JLabel("Mobile Number: ");
    l4.setForeground(Color.white);
    l4.setFont(new Font("Serif", Font.BOLD, 15));
    l4.setBounds(100,250,150,20);

    l5= new JLabel("Mother's Name: ");
    l5.setForeground(Color.white);
    l5.setFont(new Font("Serif", Font.BOLD, 15));
    l5.setBounds(100,300,150,20);

    l6= new JLabel("Mobile Number: ");
    l6.setForeground(Color.white);
    l6.setFont(new Font("Serif", Font.BOLD, 15));
    l6.setBounds(100,350,150,20);

    l7= new JLabel("Village: ");
    l7.setForeground(Color.white);
    l7.setFont(new Font("Serif", Font.BOLD, 15));
    l7.setBounds(100,400,150,20);

    l8= new JLabel("Police Station: ");
    l8.setForeground(Color.white);
    l8.setFont(new Font("Serif", Font.BOLD, 15));
    l8.setBounds(100,450,150,20);

    l9= new JLabel("District: ");
    l9.setForeground(Color.white);
    l9.setFont(new Font("Serif", Font.BOLD, 15));
    l9.setBounds(100,500,150,20);

    l10= new JLabel("Blood Group: ");
    l10.setForeground(Color.white);
    l10.setFont(new Font("Serif", Font.BOLD, 15));
    l10.setBounds(100,550,150,20);

    l11= new JLabel("Department: ");
    l11.setForeground(Color.white);
    l11.setFont(new Font("Serif", Font.BOLD, 15));
    l11.setBounds(600,100,150,20);

    l12= new JLabel("Series: ");
    l12.setForeground(Color.white);
    l12.setFont(new Font("Serif", Font.BOLD, 15));
    l12.setBounds(600,150,150,20);

    l13= new JLabel("Roll Number: ");
    l13.setForeground(Color.white);
    l13.setFont(new Font("Serif", Font.BOLD, 15));
    l13.setBounds(600,200,150,20);

    l14= new JLabel("CGPA: ");
    l14.setForeground(Color.white);
    l14.setFont(new Font("Serif", Font.BOLD, 15));
    l14.setBounds(600,250,150,20);

    l15= new JLabel("Room Number: ");
    l15.setForeground(Color.white);
    l15.setFont(new Font("Serif", Font.BOLD, 15));
    l15.setBounds(600,300,150,20);





    tf1= new JTextField();
    tf1.setBounds(300,100,200,20);

    tf2= new JTextField();
    tf2.setBounds(300,150,200,20);

    tf3= new JTextField();
    tf3.setBounds(300,200,200,20);

    tf4= new JTextField();
    tf4.setBounds(300,250,200,20);

    tf5= new JTextField();
    tf5.setBounds(300,300,200,20);

    tf6= new JTextField();
    tf6.setBounds(300,350,200,20);

    tf7= new JTextField();
    tf7.setBounds(300,400,200,20);

    tf8= new JTextField();
    tf8.setBounds(300,450,200,20);

    tf9= new JTextField();
    tf9.setBounds(300,500,200,20);

    tf10= new JTextField();
    tf10.setBounds(300,550,200,20);

    tf11= new JTextField();
    tf11.setBounds(710,100,200,20);

    tf12= new JTextField();
    tf12.setBounds(710,150,200,20);

    tf13= new JTextField();
    tf13.setBounds(710,200,200,20);

    tf14= new JTextField();
    tf14.setBounds(710,250,200,20);

    tf15= new JTextField();
    tf15.setBounds(710,300,200,20);



    tf1.setEditable(false);
    tf2.setEditable(false);
    tf3.setEditable(false);

    tf4.setEditable(false);
    tf5.setEditable(false);
    tf6.setEditable(false);

    tf7.setEditable(false);
    tf8.setEditable(false);
    tf9.setEditable(false);

    tf10.setEditable(false);
    tf11.setEditable(false);
    tf12.setEditable(false);

    tf13.setEditable(false);
    tf14.setEditable(false);
    tf15.setEditable(false);






    try {  

        Class.forName("com.mysql.jdbc.Driver");  

        Connection con=DriverManager.getConnection(  
        "jdbc:mysql://localhost:3306/hostel_management","root","");  

        //here project is database name, root is username and password is empty 

        Statement stmt=con.createStatement();  

        ResultSet rs=stmt.executeQuery("select * from student_info where roll_no = '" + textfield.getText() + "'");  

        //if(rs.next()=null)
            //JOptionPane.showMessageDialog(null, "No Available Seat. Please Select Another Room.", "Warning", JOptionPane.ERROR_MESSAGE);
        int count= 0;










        while(rs.next())  
        {

             count++;


             tf1.setText(rs.getString(1));
             tf1.setHorizontalAlignment(JTextField.CENTER);

             tf2.setText(rs.getString(2));
             tf2.setHorizontalAlignment(JTextField.CENTER);

             tf3.setText(rs.getString(3));
             tf3.setHorizontalAlignment(JTextField.CENTER);

             tf4.setText(rs.getString(4));
             tf4.setHorizontalAlignment(JTextField.CENTER);

             tf5.setText(rs.getString(5));
             tf5.setHorizontalAlignment(JTextField.CENTER);

             tf6.setText(rs.getString(6));
             tf6.setHorizontalAlignment(JTextField.CENTER);

             tf7.setText(rs.getString(7));
             tf7.setHorizontalAlignment(JTextField.CENTER);

             tf8.setText(rs.getString(8));
             tf8.setHorizontalAlignment(JTextField.CENTER);

             tf9.setText(rs.getString(9));
             tf9.setHorizontalAlignment(JTextField.CENTER);

             tf10.setText(rs.getString(10));
             tf10.setHorizontalAlignment(JTextField.CENTER);

             tf11.setText(rs.getString(11));
             tf11.setHorizontalAlignment(JTextField.CENTER);

             tf12.setText(rs.getString(12));
             tf12.setHorizontalAlignment(JTextField.CENTER);

             tf13.setText(rs.getString(13));
             tf13.setHorizontalAlignment(JTextField.CENTER);

             tf14.setText(rs.getString(14));
             tf14.setHorizontalAlignment(JTextField.CENTER);

             tf15.setText(rs.getString(15));
             tf15.setHorizontalAlignment(JTextField.CENTER);



             Blob blob = rs.getBlob(16);
             int blobLength = (int) blob.length();  

             byte[] bytes = blob.getBytes(1, blobLength);
            //blob.free();
             BufferedImage image = ImageIO.read(new ByteArrayInputStream(bytes));


             ImageIcon icon = new ImageIcon(bytes); // you can read straight from byte array
             l16 = new JLabel(icon);
             l16.setBounds(620, 350, 250, 250);
             add(l16);



             //add(frame_imagelabel);
              add(l1);
              add(tf1);
              add(l2);
              add(tf2);
              add(l3);
              add(tf3);
              add(l4);
              add(tf4);
              add(l5);
              add(tf5);
              add(l6);
              add(tf6);
              add(l7);
              add(tf7);
              add(l8);
              add(tf8);
              add(l9);
              add(tf9);
              add(l10);
              add(tf10);
              add(l11);
              add(tf11);
              add(l12);
              add(tf12);
              add(l13);
              add(tf13);
              add(l14);
              add(tf14);
              add(l15);
              add(tf15);



              add(frame_imagelabel);
              pack();
              setSize(1000,700);


        }


        //if(im!=null)
        //JOptionPane.showMessageDialog(null, "No image", "Warning", JOptionPane.ERROR_MESSAGE);


        if(count==0)
            JOptionPane.showMessageDialog(null, "This Student is not a member of this hall.", "Warning", JOptionPane.ERROR_MESSAGE);


        con.close();  

        } catch(Exception ex){ JOptionPane.showMessageDialog(null, ex, "Error", JOptionPane.ERROR_MESSAGE); }  


    }

Answer 1

点击按钮后，您可以添加多个JLabel和JTextFields：

    f(e.getSource()==button)
        {

        l1= new JLabel("Name: ");
        l1.setForeground(Color.white);
        l1.setFont(new Font("Serif", Font.BOLD, 15));
        l1.setBounds(100,100,150,20);
        //l1.setLabelFor(tf1);

        .....
        .....
        .....

        l15= new JLabel("Room Number: ");
        l15.setForeground(Color.white);
        l15.setFont(new Font("Serif", Font.BOLD, 15));
        l15.setBounds(600,300,150,20);

        tf1= new JTextField();
        tf1.setBounds(300,100,200,20);
        .....
        .....
        .....
        tf15= new JTextField();
        tf15.setBounds(300,100,200,20);
   }

然后您将JLabel和JTextField添加到Frame。

每次按下按钮时，您都在执行这些步骤。

现在，您第一次输入滚动号码并按下按钮以查看该学生信息，该代码会向JLabel添加一些JTextField和Frame。

当您尝试查看第二次时，此代码会再次添加一些JLabel和JTextField，而不会删除第一次添加的其他JLabel和JTextField。然后在第二次，创建JLabel和JTextFields将添加到框架下方，因此您无法看到它，因为它超出了框架大小。

因此，您需要删除第一次创建的所有JLabel和JTextField。

因此您应该在添加之前删除所有组件（JLabel和JTextField）：

如果您在班级中延伸JFrame：请尝试此

if(l1!=null){
remove(l1);
}
...
...
...

if(l15!=null){
remove(l15);
}

if(tf1!=null){
remove(tf1);
}
...
...
...

if(tf15!=null){
remove(tf15);
}

但这不是更好的解决方案吗

如果您初始化JLabel中的所有JTextField和Constructor，那就更好了。

单击按钮时，只需将文本设置为它们。

l1.setText(your_value_from_db);//l1 is JLabel type variable

tf.setText(your_value_from_db);//tf is JTextField type variable

单击按钮不会更新JTextField

1 个答案: