@UiHandler("btnSuccessTxtBox")
 void onSuccessTxtBox(ClickEvent e) {
   txtBox.setSuccess("This is a success message for text box.");
 }
 @UiHandler("btnClearTxtBox")
 void onClearTxtBox(ClickEvent e) {
   txtBox.clearErrorOrSuccess();
 }
 @UiHandler("btnErrorTxtBox")
 void onErrorTxtBox(ClickEvent e) {
   txtBox.setError("This is an error message for text box.");
 }