retrieve mysql data when i change combobox item in java

Question

I use the following code to retrieve data from msysql database to a JComboBox. It was working properly. My problem is when I execute this code, if I click jCombobox, only one item is shown and it displays the related data from database.. it is not getting all the ids from database to Combobox, so that i can select a particular id and display related data.

package Swings;

import java.awt.Color;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.sql.*;

import javax.swing.*;

class Frame3 extends JFrame implements ActionListener,ItemListener
{
private JFrame frame;
JPanel panel=new JPanel();
JButton btn1,btn2,btn3;
JLabel l1, l2, l3, l4, l5, l6, l7;
private JComboBox SummonIdbox;
private JTextField txtcarLicenceNo;
private JTextField txtamount;
private JTextField txtdateFined;
private JTextField txtlocation;
private JTextField txtofficerInCharge;
  String dbURL = "jdbc:mysql://localhost:3306/cpss";
  String username ="root";
  String password = "root";

  Connection c = null;
  Statement st = null;
  ResultSet rs = null;


Frame3()
{

        setVisible(true);
        setSize(700, 700);
        setLayout(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setTitle("CPSS Application");

        l1 = new JLabel("Update Summon Details");
        l1.setForeground(Color.blue);
        l1.setFont(new Font("Serif", Font.BOLD, 20));

        l2 = new JLabel("SummonId");
        l3 = new JLabel("Car LicenceNo:");
        l4 = new JLabel("Amount");
        l5 = new JLabel("DateFined");
        l6 = new JLabel("Location");
        l7 = new JLabel("Officer Incharge");

        SummonIdbox = new JComboBox();
        txtcarLicenceNo = new JTextField();
        txtamount = new JTextField();
        txtdateFined = new JTextField();
        txtlocation = new JTextField();
        txtofficerInCharge=new JTextField();

        btn1 = new JButton("Update");
        btn2 = new JButton("Clear");
        btn3=  new JButton("Home");

        btn1.addActionListener(this);
        btn2.addActionListener(this);
        btn3.addActionListener(this);
        SummonIdbox.addItemListener(this);


        l1.setBounds(500, 30, 400, 30);
        l2.setBounds(400, 70, 200, 30);
        l3.setBounds(400, 110, 200, 30);
        l4.setBounds(400, 150, 200, 30);
        l5.setBounds(400, 190, 200, 30);
        l6.setBounds(400, 230, 200, 30);
        l7.setBounds(400, 270, 200, 30);

        SummonIdbox.setBounds(500, 70, 200, 30);
        txtcarLicenceNo.setBounds(500, 110, 200, 30);
        txtamount.setBounds(500, 150, 200, 30);
        txtdateFined.setBounds(500, 190, 200, 30);
        txtlocation.setBounds(500, 230, 200, 30);
        txtofficerInCharge.setBounds(500, 270, 200, 30);
        btn1.setBounds(450, 350, 100, 30);
        btn2.setBounds(600, 350, 100, 30);
        btn3.setBounds(750, 350, 100, 30);

        add(l1);
        add(l2);
        add(SummonIdbox);
        add(l3);
        add(txtcarLicenceNo);
        add(l4);
        add(txtamount);
        add(l5);
        add(txtdateFined);
        add(l6);
        add(txtlocation);
        add(l7);
        add(txtofficerInCharge);
        add(btn1);
        add(btn2);
        add(btn3);
        add_summonid(SummonIdbox);

    }

@Override
public void actionPerformed(ActionEvent ae ) {
    if(ae.getSource() == btn2)
       {

         txtcarLicenceNo.setText("");
         txtamount.setText("");
         txtdateFined.setText("");
         txtlocation.setText("");
         txtofficerInCharge.setText("");
        }

else if (ae.getSource() == btn3)
     {
        SwingMenu s=new SwingMenu();
        s.setSize(800,800);
        s.setVisible(true);
     }

    }

void add_summonid(JComboBox SummonIdbox)
{
        try
        {
             //Class.forName("com.mysql.jdbc.Driver");
             //System.out.println("Driver is loaded");
              c = DriverManager.getConnection(dbURL, username, password);
             System.out.println("Connection created");
             st=c.createStatement();
             rs=st.executeQuery("select Summonid from summon");
             while(rs.next())
                SummonIdbox.addItem(rs.getInt(1));   
            // c.close();
          }
        catch (Exception ex) 
         {
             System.out.println(ex);
         }
     }

@Override
public void itemStateChanged(ItemEvent ie) {

    int item=  (Integer) SummonIdbox.getSelectedItem();
    System.out.println(item);
    String sql="select carLicenceNo,amount,dateFined,location,officerIncharge from summon where summonId='"+item+"'";

try {
        PreparedStatement pst = c.prepareStatement(sql);
        //pst.setInt(1,item);
        rs=pst.executeQuery();
        while(rs.next())
            {
            txtcarLicenceNo.setText(rs.getString(1));
            txtamount.setText(String.valueOf((rs.getDouble(2))));
            txtdateFined.setText(rs.getString(3));
            txtlocation.setText(rs.getString(4));
            txtofficerInCharge.setText(rs.getString(5));
            /*System.out.println(rs.getString(1));
            System.out.println(rs.getDouble(2));
            System.out.println(rs.getString(3));
            System.out.println(rs.getString(4));
            System.out.println(rs.getString(5));*/

            }


    } catch (SQLException e) {

        e.printStackTrace();
    }

    }
}