Textfield data to another class

[subrat_p]

public class examination extends javax.swing.JFrame {
    public Connection con;
    public Statement stmt;
    public ResultSet rs;
    public String sname,sid,sub;

    /** Creates new form examination */
    public examination() {
        welcome wl=new welcome();
        String stname=wl.regdno.getSelectedText();
        
        try
                {
                    Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
                    con=DriverManager.getConnection("jdbc:odbc:exam");
                    Statement stmt=con.createStatement();
                    ResultSet rs=stmt.executeQuery("SELECT * FROM student where sno='"+stname+"'");
                    while(rs.next())
                    {
                    sid=rs.getString(1);
                    sname=rs.getString(2);
                    }

                }
                catch(ClassNotFoundException e)  {
 			System.err.println("Failed to load driver");
 			e.printStackTrace();
                }catch(SQLException e){
 			System.err.println("Unable to connect");
 			e.printStackTrace();}
                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">//GEN-BEGIN:initComponents
    private void initComponents() {

        jPanel1 = new javax.swing.JPanel();
        stname = new javax.swing.JLabel("Student Name:"+sname);

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jPanel1.setBackground(new java.awt.Color(255, 255, 255));

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(stname, javax.swing.GroupLayout.PREFERRED_SIZE, 216, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(174, Short.MAX_VALUE))
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(stname, javax.swing.GroupLayout.PREFERRED_SIZE, 18, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(271, Short.MAX_VALUE))
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

        pack();
    }// </editor-fold>//GEN-END:initComponents

    /**
    * @param args the command line arguments
    */
    public static void ex() {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new examination().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify//GEN-BEGIN:variables
    private javax.swing.JPanel jPanel1;
    private javax.swing.JLabel stname;
    // End of variables declaration//GEN-END:variables

}

Where welcome is another class where I have a text field named "regdno". Now I want to get the data what I put into the textfield to this class and get student name from database and show in a label. In this code there is no error but in the particular label its shows null value. If I write the SQL query without where clause its work perfectly but I want to use with where clause.

Thank You

[javaAddict]

Of course you get null because the query doesn't return anything! Try to print the argument of the query or better yet the query itself:

System.out.println("SELECT * FROM student where sno='"+stname+"'");

You will also need to close the connection, the statement and the resultset before proceeding.
I also don't agree with your logic not do I know what the welcome class has inside. Does the regdno.getSelectedText() has any value when you call the (new welcome()) ? Because I believe that when you do the regdno is empty. And even if you do enter value to that text, you need to "send" that value to your query by clicking a button or something.

For starters, fix your DB connection.
Create a separate class like this:

public class Student {
  private String sid = null;
  private String sname = null;

  public Student() {

  }

  // add get, set methods or make the above public (Better go with the get/set methods):
  // example:
  public String getSid() {
    return sid;
  }
}

Then

public Student getStudent(String stname) throws Exception {
Student S = null;
Statement stmt = null;
ResultSet rs = null;
Connection con = null;
  try {

Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
con=DriverManager.getConnection("jdbc:odbc:exam");
stmt=con.createStatement();
rs=stmt.executeQuery("SELECT * FROM student where sno='"+stname+"'");
                    
if(rs.next()) {
 S = new Student();

 S.setSid(rs.getString(1));
 S.setSname(rs.getString(2));
}

  } catch (Exception e) {
    throw e;
  } finally {
    if (rs!=null) rs.close();
    if (stmt!=null) stmt.close();
    if (con!=null) con.close();
  }
return S;
}

I would suggest that you call that method whenever you want to get data from the DB and use that methodology for other cases.
Also I would suggest to remove the (new welcome()) from that class.
I would suggest, in the welcome class to have a text and a button; when you click the button, take the value of the text and pass it as argument to the examination class:
IN THE welcome CLASS

public void buttonclicked(..) {
  // take the text value
  String stname = ...
  examination ex = new examination(stname);
  ex.setVisible(true);
}

And:
IN THE examination CLASS

Student student = null;

// constructor of the examination
public examination(String stname) {
  try {
    student = getStudent(stname);
    if (student==null) {
      // student not found
    }
  } catch (Exception e) {
   // display error message
  }
}