Connection dbcon = null;
    try {
        Class.forName("oracle.jdbc.driver.OracleDriver");
        dbcon = DriverManager.getConnection("
             jdbc:oracle:thin:@localhost:1521:XE", "USERNAME", "PASSWORD");
        Statement st = dbcon.createStatement();
        String combo = "Select EMP_IDNUM from employees";
        ResultSet res = st.executeQuery(combo);
        while(res.next()){
            String ids = res.getString("EMP_IDNUM");
            String [] str = new String[]{ids};
            cboId = new JComboBox(str);
        }
    } catch (Exception d) {
        System.out.println(d);
    }

String [] str = new String[]{ids};

if(rs.getRow()>0){
 String [] str = new String[res.getRow()];
 int i=0;
 while(res.next()){
   str[i++] = res.getString("EMP_IDNUM");
 }
}
JComboBox jcb = new JComboBox(str);

Vector v = new Vector();
while(res.next()){
    String ids = res.getString("EMP_IDNUM");
    v.add(ids)
}
JComboBox jcb = new JComboBox(v);

try {

} catch (Exception d) {
    System.out.println(d);
} finally {
    try {
        st.close()
        res.close()
        dbcon.close()
    } catch (Exception d) {
        //not important
    }
}