Javafx - preenchendo um ArrayList com combox

Aqui está um exemplo de como usar o combox do
javafx para preencher um ArrayList.
O primeiro número escolhido será o tamanho
do ArrayList, e do segundo elemento em diante 
até o tamanho serão inseridos na lista.

Veja abaixo uma imagem do programa em execução: 

Veja abaixo o código do programa:

import java.util.ArrayList;

import javafx.application.Application;

import javafx.scene.Scene;

import javafx.scene.canvas.Canvas;

import javafx.scene.canvas.GraphicsContext;

import javafx.scene.control.Button;

import javafx.stage.Stage;

import javafx.scene.paint.Color;

import javafx.scene.layout.Pane;

import javafx.scene.text.Font;

import javafx.scene.text.FontWeight;

import javafx.geometry.Insets;

import javafx.scene.control.*;

import javafx.scene.layout.GridPane;

import javafx.beans.value.ChangeListener;

import javafx.beans.value.ObservableValue;

public class PROJETO extends Application {

     static int k = 0, l = 0;

     public static int TAM = 100, fim, tam = 0;

     static Canvas canvas = new Canvas ( 620, 350 );

     static GraphicsContext ctx = canvas.getGraphicsContext2D ( );

     static Pane ro_ot = new Pane ( );

     static Scene sce_ne = new Scene ( ro_ot, 620, 350 );

     static Button btn_1 = new Button ( "TECLE ENTER" );

     @SuppressWarnings ( "rawtypes" )

     static final ComboBox cb = new ComboBox ( );

     static GridPane grid = new GridPane ( );

     static Boolean y = false;

///////////////////////////////////////////////////////////////////////////

     public static void Informe ( ) {

         ctx.setFont ( Font.font ( "Arial", FontWeight.NORMAL, 13 ) );

         ctx.setFill ( Color.RED );

         ctx.fillText ( "Por: ", 200, 242 );

         ctx.setFill ( Color.BLUE );

         ctx.fillText ( "Samuel Lima", 240, 242 );

         ctx.setFill ( Color.BLACK );

         ctx.fillText ( "sa_sp10@hotmail.com", 200, 260 );

         ctx.setFill ( Color.RED );

         ctx.fillText ( " MUITO OBRIGADO", 250, 320 );

     }

     // ////////////////////////////////////////////////////////////////////////

     public static int Inf_quant ( ArrayList < Integer > arr ) {

         ctx.setFont ( Font.font ( "Arial", FontWeight.NORMAL, 15 ) );

         int i;

         StringBuilder st = new StringBuilder ( );

         k++;

         ctx.clearRect ( 180, 70, 200, 20 );

         ctx.clearRect ( 240, 70, 20, 20 );

         ctx.clearRect ( 260, 70, 200, 20 );

         ctx.clearRect ( 180, 70, 400, 20 );

         ctx.clearRect ( 180, 90, 400, 20 );

         ctx.setFill ( Color.BLUE );

         ctx.fillText ( "Insira o ", 190, 80 );

         ctx.setFill ( Color.RED );

         ctx.fillText ( " " + ( k ) + " º", 240, 80 );

         ctx.setFill ( Color.BLUE );

         ctx.fillText ( "número", 275, 80 );

         arr.add ( fim  );

         st.append ( arr );

         if ( k == tam + 2 ) {

              st = new StringBuilder ( );

              ctx.clearRect ( 180, 70, 400, 20 );

              for ( i = 1; i < tam + 2; i++ ) {

                   if ( arr.get ( i )  != ' ' )

                        if ( arr.get ( i ) % 10 == 0 )

                            st.append ("\n");

                   if ( arr.get ( i ) >= 0 && arr.get ( i ) <= 9 )

                        st.append ( "0" );

                   System.out.printf ( "%3d", arr.get ( i ) );

                   st.append ( arr.get ( i ) + "\t");

              }

              ctx.setFill ( Color.BLUE );

              ctx.fillText ( "Veja abaixo o ArrayList preenchido", 200, 80 );

              ctx.setFill ( Color.RED );

              ctx.fillText ( " " + st, 160, 110 );

              Informe ( );

         }

         return 0;

     }

     // ////////////////////////////////////////////////////////////////////////

     @SuppressWarnings ( "unchecked" )

     public static int Array_1 ( ArrayList < Integer > arr ) {

         cb.setStyle ( "-fx-padding: 5;" + "-fx-border-style: solid inside;"

                   + "-fx-border-width: 2;" + "-fx-border-insets: 5;"

                   + "-fx-border-radius: 5;" + "-fx-border-color: black;" );

         int i = 0;

         do {

              i++;

              //total de linhas visíveis

              cb.setVisibleRowCount ( 10 );

              cb.getItems ( ).addAll ( i );

         } while ( i <= TAM );

         cb.getSelectionModel ( ).selectedIndexProperty ( )

         .addListener ( new ChangeListener < Number > ( ) {

              @SuppressWarnings ( "rawtypes" )

              public void changed ( ObservableValue ov, Number value,

                        Number new_value ) {

                   if ( y == false ) {

                        tam = new_value.intValue ( );

                        y = true;

                   }

                   if ( y == true ) {

                        fim = new_value.intValue ( );

                        fim = fim + 1;

                   }              

                   Inf_quant ( arr );

              }

         } );

         grid.add ( cb, 1, 1 );

         return 0;

     }

     // ////////////////////////////////////////////////////////////////////////

     public void start ( Stage stage ) {

         ArrayList < Integer > arr = new ArrayList < > ( );

         ctx.setFont ( Font.font ( "Arial", FontWeight.NORMAL, 15 ) );

         stage.setTitle ( "JAVAFX - PREENCHENDO UM ARRAYLIST COM COMBOX" );

         //Criando moldura e dando efeitos

         ro_ot.setStyle ( "-fx-padding: 5;" + "-fx-border-style: solid inside;"

                   + "-fx-border-width: 12;" + "-fx-border-insets: 5;"

                   + "-fx-border-radius: 5;" + "-fx-border-color: black;"

                   + "-fx-background: lightblue;");

         ctx.setFill ( Color.RED );

         ctx.fillText ( "PREENCHENDO UM ARRAYLIST COM COMBOX", 150, 50 );

         ctx.setFont ( Font.font ( "Arial", FontWeight.NORMAL, 15 ) );

         ctx.setFill ( Color.BLACK );

         ctx.fillText ( "Escolha no combox o total de números", 190, 80 );

         ctx.setFill ( Color.BLACK );

         ctx.fillText ( "que deseja inserir no ArrayList", 190, 100 );

         Array_1 ( arr );

         grid.setPadding ( new Insets ( 15, 15, 60, 15 ) );

         ro_ot.getChildren ( ).addAll ( canvas );

         ro_ot.getChildren ( ).addAll ( grid );

         stage.setScene ( sce_ne );

         stage.show ( );

     }

     // ////////////////////////////////////////////////////////////////////////

     public static void main ( String [ ] args ) {

         Application.launch ( args );

     }

}