请教JComboBox和数据库的刷新问题，thanks！

我在进行jcombobox和数据库操作的时候，通过点击“操作”按纽进行籍贯的添加、删除和修改，在数据库里都可以很成功的实现，但是jcombobox里没有实现刷新，请问怎么改才能是对数据库刷新后jcombobox里能够自动的刷新，谢谢




import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.tree.*;
import java.sql.*;
import java.util.*;
import java.util.Vector.*;



public class combobox1 extends JFrame implements ActionListener
{
public static void main(String args[])
{
new combobox1();
}
private Connection con1;
private Statement state1;
private ResultSet rst1;
private String str5="";
private JComboBox cp6;
private Vector rec_vector;
private Container c;
private JButton b1;



public combobox1()
{
super("输入国防生基本资料");
Container c=getContentPane();
c.setLayout(null);
connect_db();
b1=new JButton("操作");
b1.addActionListener(this);
b1.setBounds(200,50,80,30);
c.add(b1);


rec_vector = new Vector();
try
{
String query="SELECT nativeplaceName FROM nativeplace";
rst1= state1.executeQuery(query);
while(rst1.next())
{
str5= rst1.getString(1);
rec_vector.addElement(str5);
}
}
catch(SQLException e)
{
e.printStackTrace();
}
cp6=new JComboBox(rec_vector);
cp6.setBounds(10,10,150,25);
c.add(cp6);


setBounds(150,100,300,300);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);


addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e)
{
System.exit(0);

close_db();
setVisible(false);
}
}
);
}

public void connect_db()
{

try
{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
}
catch(ClassNotFoundException e1)
{
e1.printStackTrace();
}

try
{
con1=DriverManager.getConnection("jdbc:odbc:空军国防生");
state1=con1.createStatement();
}

catch(SQLException e2)
{
e2.printStackTrace();
}
}


public void actionPerformed(ActionEvent e)
{
if(e.getSource()==b1)
{
new addNativeplace();
}
}

public void close_db()
{
try
{
con1.close();
state1.close();
}
catch(SQLException e5)
{
e5.printStackTrace();
}

}

}