retrieving data in to the dropdown box from postgresql database in core java

hi., i just need to correct my codes.somebody help me to clear the error to bring a right of codes to execute.Thanks in advance.
//first page
    import java.awt.*;
    import java.sql.SQLException;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import javax.swing.*;
    class gwf extends Frame implements ActionListener
    { 
        public Label l1,l2,l3;
        public TextField tf1,tf2,tf3;
        public JComboBox c1,c2;
        public Button b1,b2;
        public Panel p1,p2;
        String s1,s2;
        gwf()
        {    setLayout(new GridLayout(5,1));
             setTitle("FIRST PAGE");
            l1 = new Label("Choose Department");
            c1 = new JComboBox();
            c1.addItem("--select--");
            c1.addItem("Welfare");
            c1.addItem("Revenue");
            c1.addItem("State office");
            c1.addItem("Public");
            c1.addItem("Corporation");
            p1 = new Panel();
            p2 = new Panel();
            b1 = new Button("SUBMIT");
            p1.add(l1);
            p1.add(c1);
            p2.add(b1);
            add(p1, "Center");
            add(p2, "South");
            b1.addActionListener(this);
            setSize(500, 500);
            setVisible(true);
        }
        public void actionPerformed(ActionEvent e) 
        {
            gwf1 gw = new gwf1(s1);
            dispose();
        }
        public static void main(String[] args) throws SQLException 
        {
            gwf g = new gwf(); }
//second page
    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.ResultSet;
    import java.sql.Statement;

    class gwf1 extends Frame implements ActionListener
    {
        private static final String String =null;
        Label l1;
        TextField t1;
        JComboBox c1,c2;
        Panel  p1,p2;
        Button b1;
        String s1, s2;
        Statement st;
        ResultSet rs;
        Connection con;
      public void apply()
       {
        try
           {
                Class.forName("org.postgresqlANSI.Driver");
            con = DriverManager.getConnection("jdbc:postgresqlANSI://localhost:5432/departments","postgres", "postgres");
            ResultSet rs=st.executeQuery("SELECT role_name from role WHERE dept_id=1234");
                if(rs!=null)
                {while(rs.next())
                {
                   c1.addItem(rs.getString("role_name"));
                }
                }
           }
           catch(Exception e)
           {
                 e.printStackTrace();
           }
       }
        public gwf1(String s1)
        {
            this.s1 = s1;
            setLayout(new GridLayout(5, 1));
            setTitle("Second Page");
            l1 = new Label("Enter Role");
            c1 = new JComboBox();
            c1.addItem("--select--");
            b1 = new Button("SUBMIT");
            p1 = new Panel();
            p2 = new Panel();
            p1.add(l1);
            p1.add(c1);
            p2.add(b1); 
            add(p1, "Center");
            add(p2, "South");
            b1.addActionListener(this);
            setSize(400, 500);
            setVisible(true);
          }
        public void actionPerformed(ActionEvent e1) 
        {
            JOptionPane.showMessageDialog(this, "The generated Id is:");
            dispose();
            gwf2 gp = new gwf2();
        }
    }

March 14, 2011 at 11:57 AM

We have used Mysql database:

import java.sql.*;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class  JComboBoxExample{
    public static void main(String[] args){
        JFrame f=new JFrame();
        f.setLayout(null);
        JLabel lab=new JLabel("Course Items:");
        final JComboBox combo=new JComboBox();
        combo.addItem("--Select--");
        try{
        Class.forName("com.mysql.jdbc.Driver");
           Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "root");
           Statement st=con.createStatement();
           ResultSet rs=st.executeQuery("select * from student");
           while(rs.next()){
           combo.addItem(rs.getInt("id"));
           }
        }
        catch(Exception e){}
        JButton b=new JButton("Get");
        lab.setBounds(20,20,100,20);
        combo.setBounds(120,20,150,20);
        b.setBounds(120,50,80,20);
        b.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
        String value = combo.getSelectedItem().toString();
        JOptionPane.showMessageDialog(null,"You have selected '"+value+"' from ComboBox");
         }
        });
        f.add(lab);
        f.add(combo);
        f.add(b);
        f.setVisible(true);
        f.setSize(300,120);
    }
}