java - throw Exception in lambda(or equivalent) - javafx -

i trying popup come asking user if wish exit program everytime click exit button (x in the top left corner). using fxml , have throw exception when try load popup primarystage.setoncloserequest(new eventhandler<windowevent>{} keep getting unhandled exception error when throw error in method calling from. have tried try , catch , while there isn't error code doesn't run. trying see if can wrap method in can maybe around exception nothing has seemed work. there way use setoncloserequest thrown exception?

public class main extends application  {      @override     public void start(stage primarystage)throws exception  {         file f = new file("goal.txt");         boolean bool = false;          if (f.exists() )         {             fxmlloader loader = new fxmlloader(getclass().getresource("mainpage.fxml"));             parent root = loader.load();             primarystage.settitle("money saver program");             primarystage.setscene(new scene(root, 600, 400));             primarystage.show();         }         else         {             bool = f.createnewfile();             parent root = fxmlloader.load(getclass().getresource("openingpage.fxml"));             primarystage.settitle("money saver program");             primarystage.setscene(new scene(root, 638, 400));             primarystage.show();         }         primarystage.setoncloserequest(new eventhandler<windowevent>() {              public void handle(windowevent event) {                 event.consume();                 closeprogram();             }         });      }      public static void main(string[] args) throws exception {         launch(args);     }      public void closeprogram(){         try{internalcloseprogram();}catch (exception e){}     }      public void internalcloseprogram()throws exception{         fxmlloader fxmlloader = new fxmlloader(getclass().getresource("finalexitmessage.fxml"));         parent root = fxmlloader.load();         stage stage = new stage();         stage.setscene(new scene(root));         stage.settitle("money saver program");         stage.show();     }  } 

you cannot throw checked exception lambda expression/anonymus class, if exception not assignable exception in throws clause of abstract method of functional interface.

what done throwing new unchecked exception has exception it's cause:

try{     internalcloseprogram(); } catch (exception e){      throw new illegalstateexception("something went wrong", e); } 

however nothing happening seems indication loading finalexitmessage.fxml failed. note: "swallowing" exception not idea, unless know sure can safely ignored , don't need information debugging.

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furthermore consuming event in oncloserequest call, tell javafx ignore attempt close window. need close stage yourself, in case want close it, using

primarystage.close(); 

you use

platform.exit(); 

from stage shown in internalcloseprogram method.

also wait user interact new stage calling showandwait instead of show on new stage wait until new stage closed.

additional recommendation: use modality block events primary stage while new stage shown.

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the following example asks, if window should closed using alert. showandwait method of alert different stage.showandwait: returns optional<buttontype> returning user pick. stage you'd need access controller result.

@override public void start(stage primarystage) {     scene scene = new scene(new group(), 100, 100);      primarystage.setoncloserequest(evt -> {         alert alert = new alert(alert.alerttype.confirmation, "do want close applicetion?", buttontype.yes, buttontype.no);         buttontype result = alert.showandwait().orelse(buttontype.no);          if (buttontype.no.equals(result)) {             // no choice or no clicked -> don't close             evt.consume();         }     });     primarystage.setscene(scene);     primarystage.show(); }