java - select items in ListView<items> and return null in JavaFX -

shapefx class contains arraylist shapes

    public class shapefx {          private arraylist<shapes> shapes;          public shapefx () {             this.shapes= new arraylist<>();         }          public shapefx (arraylist<shapes> shapes) {             this.shapes= shapes;         }          public arraylist<shapes> getshapes() {             return this.shapes;         }          public void setshapes(arraylist<shapes> shapes) {             this.shapes= shapes;         }          @override         public int size() {             return this.shapes.size();         }          @override         public void add(shapes element) {             this.shapes.add(element);         }          @override         public void remove(shapes element) {             if (element != null) {                 this.shapes.remove(element);             }          }   @override     public string tostring() {         stringbuilder str = new stringbuilder();          iterator itr = this.formageometricas.iterator();         while (itr.hasnext()) {             str.append(itr.tostring());         }         return str.tostring();     }      } 

here have small example of 2 events in javafx buttons create shapes , remove shapes, method add(shapes element) works, method remove(shapes element) not work because after shapes created, when try remove shapes, receive message doesn´t exist shapes

      //in javafx       shapesfx shapesfx = new shapesfx();        observablearraylist<string> options = fxcollections.observablearraylist(                 "circle", "triangle");       combobox<string>combobox = new combobox<>(options);        button btncreate = new button("create shapes");            btncreate.setonaction(new eventhandler<actionevent>() {         @override          public void handle(actionevent t) {             //here function            object items = combobox.getselectionmodel().getselecteditem();             if (items.equals("circle")) {                 point2d p1 = new point2d(0, 0);                               //public class circle extends shapes                  shapesfx.add(new circle(p1, color.black, float.valueof(radiustextfield.gettext())));            } else if (items.equals("triangle")) {                  point2d p2 = new point2d(0, 0);                                //public class triangle extends shapes                   shapesfx.add(new triangle(p2, color.black, float.valueof(sizetextfield.gettext())));                                      }                 }); 

the error begin in part, when try select item in listview (shapes shape = list.getselectionmodel().getselecteditem();) or error in observablelist listshapes = fxcollections.observablearraylist(shapesfx.getshapes());

//or error here when made (shapesfx.getshapes()) final observablelist<shapes> listshapes = fxcollections.observablearraylist(shapesfx.getshapes());         final listview<shapes> list = new listview<>(listshapes);          button btnremove = new button("remove shapes");           btnremove.setonaction(new eventhandler<actionevent>() {             @override             public void handle(actionevent t) {                  // or error here                 shapes shape = list.getselectionmodel().getselecteditem();                 if (shape != null) {                         shapesfx.remove(shape);                 } else {                     system.out.println("doesn´t exist shapes");                 }             }         }) 

after inserting data , click on btncreate create shape, in part shape created successfully.

but when click on btnremove delete created shape, , when shapes shape = list.getselectionmodel().getselecteditem(); browse , select shape clean, , instead of shape return different null (forms != null), shape return null (and displays message doesn´t exist shapes) if no shape not created