final FormField<String> field9 = new StringTextBoxFormField();
field9.setValidator(new NotEmptyFieldValidator());
final FormField<String> field10 = new StringTextBoxFormField();
field10.setValidator(new TwinFieldValidator("Field doesn't match", field9));
form.addFormField(field1);
form.addFormField(field2);
form.addFormField(field3);
form.addFormField(field4);