public void cargar_Usuarios()
    {
        try
        {

            Class.forName("oracle.jdbc.OracleDriver");
            String query="show database;";
            JCB_USER.removeAllItems();
            JCB_USER.addItem("");
            //String base="jdbc:oracle:thin:@localhost:1521:XE";
            conexion=DriverManager.getConnection(base,user,pass);
            Statement st= conexion.createStatement();
            ResultSet rs=st.executeQuery(query);
            while(rs.next())
            {
                JCB_USER.addItem(rs.getString(0));
            }

        }
        catch(Exception ex)
        {
            ex.getMessage();
        }

    }