Mistakes with table clicked fetching from DB

Question

can you help me. I got stock in my project.. when I retrieve Resultset, it doesn't appear in field when I click on the table.. the code is below..

private void table_lectureKeyPressed(java.awt.event.KeyEvent evt) {                                         
  if(evt.getKeyCode()==KeyEvent.VK_DOWN || evt.getKeyCode()==KeyEvent.VK_UP ){

    try {
      int row=table_lecture.getSelectedRow();
      String Table_Clicked=table_lecture.getModel().getValueAt(row, 0).toString();
      String sql="Select * from Lectures where Lecture_ID='"+Table_Clicked+"' ";
      ps=con.prepareStatement(sql);
      rs=ps.executeQuery();    

      if (rs.next()) {
       try {
         String add1=rs.getString("Lecture_ID").toString();
         txt_LectureNO.setText(add1);
         String add2=rs.getString("Lecture_Name");
         txt_lecture.setText(add2);
         String add3=rs.getString("Lecture_Date");
         dtc_Date.setDateFormatString(add3);
         String add4=rs.getString("Lecture_Time");
         txt_Time.setText(add4);
         String add5=rs.getString("Lecturer");
         txt_Lecturer.setText(add5);
         String add6=rs.getString("Lecture_Place");
         txt_Place.setText(add6);
         String add7=rs.getString("Audiance");
         txt_Audiance.setText(add7);
         String add8=rs.getString("Remark");
         txp_Remarks.setText(add8);
       } catch(Exception e) {
          JOptionPane.showMessageDialog(null, e.getMessage());
        }
      }
    } catch(Exception e ){
      JOptionPane.showMessageDialog(null, e.getMessage());
    }          
  }   
}  

Any help appreciated.

Answer 1

Note your SQL statement:

"Select * from Lectures where Lecture_ID='"+Table_Clicked+"' "

This statement will be parsed in something like this:

Select * from Lectures where Lecture_ID = '1'

Tipically an ID is a numerical data type, so I suspect the problem is in your SQL statement giving you an empty result set (or causing an SQLException). In addition your query is vulnerable to SQL injection attacks.

To avoid these issues you need to use PreparedStatement properly:

int row = table_lecture.getSelectedRow();
Object tableClicked = table_lecture.getValueAt(row, 0);
String sql = "SELECT * FROM Lectures WHERE Lecture_ID = ?";
ps = con.prepareStatement(sql);
ps.setObject(1, tableClicked);
rs = ps.executeQuery();    

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Some hints on your code:

int row = table_lecture.getSelectedRow();
String Table_Clicked = table_lecture.getModel().getValueAt(row, 0).toString();

Here row is the selected row number in the view not the model, so you should request the proper value. You have two options:

Request value to the table

int row = table_lecture.getSelectedRow();
String Table_Clicked = table_lecture.getValueAt(row, 0).toString();

Convert view index in its respective model index

int row = table_lecture.getSelectedRow();
int modelIndex = table_lecture.convertRowIndexToModel(row);
String Table_Clicked = table_lecture.getModel().getValueAt(modelIndex , 0).toString();

---

It's preferable use Keybinding over KeyListeners when you're working with Swing for the reasons discussed in this topic: Key bindings vs. key listeners in Java.

In this particular case I wouldn't use keybinding either but use ListSelectionListener instead:

table_lecture.getSelectionModel().addListSelectionListener(new ListSelectionListener() {
     @Override
     public void valueChanged(ListSelectionEvent e) {
         // your code here
     }
 });

---

Database calls are time consuming tasks and may block the Event Dispatch Thread (a.k.a. EDT) causing the GUI become unresponsive. The EDT is a single and special thread where Swing components creation and update take place. To avoid block this thread consider use a SwingWorker to perform database calls in a background thread and update Swing components in the EDT. See more in Concurrency in Swing trail.

I'd suggest you take a look to the hints exposed in this answer. Summarized:

• Wrap data in a domain class.
• Use a SwingWorker to do the database calls in a background thread and update Swing components in the EDT.

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Finally but not less important, alway follow Java Code Conventions