Thread: java.lang.String cannot be cast to java.util.Hashtable

hi guys, im using the enumeration and hashtable. i have two separate classes wherein in the first one is the retrieving of data from database (the return type is enumeration) and other one is the printing of data..

PHP Code:

try
        {
            InsertSelect is = new InsertSelect();
            Hashtable ht = is.selectData("unitcode", "tblunit");
         
            Enumeration enu = ht.keys();
            while(enu.hasMoreElements())
            {
                ht = (Hashtable)enu.nextElement();
               String hehe =ht.get("field").toString();
                //cmbUnit.addItem(ht.get("field"));
               System.out.println(hehe);
            }
         } 


PHP Code:

public class InsertSelect {
    public InsertSelect() {}
    public Hashtable selectData(String field, String table){
        Hashtable hashSelect = new Hashtable();
        String query = "SELECT "+ field +" " + " FROM " +table;
        connection con = new connection(); 
        
        try{
        Statement st = con.getCon().createStatement();
        ResultSet rs = st.executeQuery(query);
             while(rs.next()){
                 hashSelect.put("field",field);
             }
        }
        catch(Exception e){System.out.println(e.getMessage());}
        return hashSelect;
    }
            
    
} 


when i run the program i got the error: java.lang.String cannot be cast to java.util.Hashtable

so what will i do? im new here?

so what will i do? sorry, i am really new in hashtable and enumeration ..

It must returned the unitcode(rl, m, RL) from a specific table of database.

i got it now, but my problem is, it only return the last data from database (ie unicode = rl, m , RL) only RL returned.. this is my revise codes:

public Hashtable selectData(String field, String table){
Hashtable hashSelect = new Hashtable();

String query = "SELECT "+ field + " FROM " +table;
System.out.println(query);
connection con = new connection();

try{
Statement st = con.getCon().createStatement();
ResultSet rs = st.executeQuery(query);
while(rs.next()){
hashSelect.put("field",rs.getString(field));

}
}
catch(Exception e){System.out.println(e.getMessage());}

System.out.println( hashSelect.keys());
return hashSelect;
}


and


try
{
InsertSelect is = new InsertSelect();
Hashtable ht = is.selectData("unitcode", "tblunit");
String str;
Enumeration enu = ht.keys();
while(enu.hasMoreElements())
{
str = (String)enu.nextElement();

cmbUnit.addItem(enu.get(str));

}
}