Javafx - calculando fatorial

Do código de uma calculadora em javafx criada
por mim mesmo, apresento esta funcionalidade
extraída, já que o código completo não foi publicado.
"Veja o vídeo no blog com o programa em execução".
Nesta versão estamos calculando o fatorial de um
 número e imprimindo os resultados num
TextField do javafx.
Alguns comentários foram colocados onde achei
necessário, aproveite este código que é uma oferta
gratuita do meu blog de java, e é indicado apenas
para estudos, para qualquer outro uso, os créditos
do autor que sou eu mesmo devem ser respeitados.    
 Veja abaixo uma imagem do programa em execução:

 Veja abaixo um vídeo com o programa em execução:

Veja abaixo o código do programa: 

import java.io.FileNotFoundException;

import javafx.application.Application;

import javafx.event.ActionEvent;

import javafx.event.EventHandler;

import javafx.geometry.Insets;

import javafx.geometry.Pos;

import javafx.scene.Group;

import javafx.scene.Node;

import javafx.scene.Scene;

import javafx.scene.canvas.Canvas;

import javafx.scene.canvas.GraphicsContext;

import javafx.scene.control.*;

import javafx.scene.input.MouseEvent;

import javafx.scene.layout.GridPane;

import javafx.scene.paint.Color;

import javafx.scene.text.Font;

import javafx.scene.text.FontWeight;

import javafx.scene.text.Text;

import javafx.stage.Stage;

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

public class PROJETO extends Application {

     static StringBuilder str1 = new StringBuilder ( );

     static Boolean x = false;

     static String key = "";

     static String str_2 = "";

     static String str_3 = "";

     static int a = 0, b = 0;

     static double i, m = 0, fact;

     static char vet; 

     private static Button btn_1           = new Button ( "1" );

     private static Button btn_2           = new Button ( "2" );

     private static Button btn_3           = new Button ( "3" );

     private static Button btn_4           = new Button ( "4" );

     private static Button btn_5           = new Button ( "5" );

     private static Button btn_6           = new Button ( "6" );

     private static Button btn_7           = new Button ( "7" );

     private static Button btn_8           = new Button ( "8" );

     private static Button btn_9           = new Button ( "9" );

     private static Button btn_0           = new Button ( "0" );

     private static Button btn_ponto       = new Button ( "." );

     private static Button btn_del         = new Button   (  );

     private static Button btn_Rquadr      = new Button ( "Fatorial" );

     static Canvas canvas = new Canvas ( 340, 280 );

     static GraphicsContext ctx = canvas.getGraphicsContext2D ( );

     static Group root = new Group ( );

     static Scene scene = new Scene ( root, 340, 280, Color.BLACK );

     static TextField name = new TextField ( );

     static GridPane grid = new GridPane ( );

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

     static Text t_0 = new Text ( );

     static Text t_1 = new Text ( );

     static Text t_2 = new Text ( );

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

     public static void Numeros ( ) {

         t_0.setFont ( Font.font ( "Arial", FontWeight.NORMAL, 20 ) );

         t_1.setFont ( Font.font ( "Arial", FontWeight.NORMAL, 25 ) );

         t_2.setFont ( Font.font ( "Arial", FontWeight.NORMAL, 15 ) );

         /////////////////////////

         t_2.setX ( 285 );//coluna

         t_2.setY ( 205 );//linha

         t_2.setText ( "←" );

     }

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

     public static Node Zero ( ) {

         t_0.setVisible ( true );

         t_0.setFill ( Color.BLACK );

         t_0.setX ( 283 );

         t_0.setY ( 108 );

         t_0.setText ( "0" );

         Reset ( );

         return t_0;

     }

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

     public static void Reset ( ) {

         if ( vet == '+' ){

              str1 = new StringBuilder ( );

              vet = ' ';

              a = 0;

              i = 0;

              str_3 = ""; 

              str_2 = "";

              x = true;

              name.clear ( );

         }

     }

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

     public static Node But_ton_del ( ) {

         btn_del.setStyle ( "-fx-font: 15 arial;"

                   + "-fx-background-color: blue;" );

         btn_del.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_del.setStyle ( "-fx-font: 15 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_del.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_del.setStyle ( "-fx-font: 15 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_del.setPrefWidth ( 40 );// Largura do botão

         btn_del.setLayoutX ( 274 );// Posição do botão coluna

         btn_del.setPrefHeight ( 37 );// altura do botão

         btn_del.setLayoutY ( 181 );// //Posição do botão linha

         btn_del.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   str1 = new StringBuilder ( );

                   name.setEditable ( true );

                   key = btn_del.getText ( );

                   name.deletePreviousChar ( );

                   name.appendText ( key );

                   str_3 = name.getText ( ).toString ( );

                   str1.append ( str_3 );

                   b = name.getText ( ).length ( );

                   if ( b == 1 ) {  

                        name.deleteText ( 0, b );

                        Zero ( );

                   }

              }

         } );

         return btn_del;

     }

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

     public static Node But_ton_9 ( ) {

         btn_9.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_9.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_9.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_9.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_9.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_9.setPrefWidth ( 40 );// Largura do botão

         btn_9.setLayoutX ( 130 );// Posição do botão coluna

         btn_9.setPrefHeight ( 20 );// altura do botão

         btn_9.setLayoutY ( 181 );// //Posição do botão linha

         btn_9.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {  

                   Reset ( );

                   t_0.setVisible ( false );

                   name.appendText ( "9" );

                   str_3 = "9";

                   a = str_3.length ( );

                   str_3 = str_3.substring ( 0, a );

                   str1.append ( str_3 );    

              }

         } );

         return btn_9;

     }

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

     public static Node But_ton_8 ( ) {

         btn_8.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_8.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_8.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_8.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_8.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_8.setPrefWidth ( 40 );// Largura do botão

         btn_8.setLayoutX ( 82 );// Posição do botão coluna

         btn_8.setPrefHeight ( 20 );// altura do botão

         btn_8.setLayoutY ( 181 );// //Posição do botão linha

         btn_8.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   Reset ( );

                   t_0.setVisible ( false );

                   name.appendText ( "8" );

                   str_3 = "8";

                   a = str_3.length ( );

                   str_3 = str_3.substring ( 0, a );

                   str1.append ( str_3 );

              }

         } );

         return btn_8;

     }

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

     public static Node But_ton_7 ( ) {

         btn_7.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_7.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_7.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_7.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_7.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_7.setPrefWidth ( 40 );// Largura do botão

         btn_7.setLayoutX ( 32 );// Posição do botão coluna

         btn_7.setPrefHeight ( 20 );// altura do botão

         btn_7.setLayoutY ( 181 );// //Posição do botão linha

         btn_7.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   Reset ( );

                   t_0.setVisible ( false );

                   name.appendText ( "7" );

                   str_3 = "7";

                   a = str_3.length ( );

                   str_3 = str_3.substring ( 0, a );

                   str1.append ( str_3 );

              }

         } );

         return btn_7;

     }

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

     public static Node But_ton_6 ( ) {

         btn_6.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_6.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_6.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_6.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_6.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_6.setPrefWidth ( 40 );// Largura do botão

         btn_6.setLayoutX ( 274 );// Posição do botão coluna

         btn_6.setPrefHeight ( 20 );// altura do botão

         btn_6.setLayoutY ( 135 );// //Posição do botão linha

         btn_6.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   Reset ( );

                   t_0.setVisible ( false );

                   name.appendText ( "6" );

                   str_3 = "6";

                   a = str_3.length ( );

                   str_3 = str_3.substring ( 0, a );

                   str1.append ( str_3 );

              }

         } );

         return btn_6;

     }

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

     public static Node But_ton_5 ( ) {

         btn_5.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_5.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_5.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_5.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_5.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_5.setPrefWidth ( 40 );// Largura do botão

         btn_5.setLayoutX ( 226 );// Posição do botão coluna

         btn_5.setPrefHeight ( 20 );// altura do botão

         btn_5.setLayoutY ( 135 );// //Posição do botão linha

         btn_5.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   Reset ( );

                   t_0.setVisible ( false );

                   name.appendText ( "5" );

                   str_3 = "5";

                   a = str_3.length ( );

                   str_3 = str_3.substring ( 0, a );

                   str1.append ( str_3 );

              }

         } );

         return btn_5;

     }

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

     public static Node But_ton_4 ( ) {

         btn_4.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_4.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_4.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_4.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_4.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_4.setPrefWidth ( 40 );// Largura do botão

         btn_4.setLayoutX ( 178 );// Posição do botão coluna

         btn_4.setPrefHeight ( 20 );// altura do botão

         btn_4.setLayoutY ( 135 );// //Posição do botão linha

         btn_4.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   Reset ( );

                   t_0.setVisible ( false );

                   name.appendText ( "4" );

                   str_3 = "4";

                   a = str_3.length ( );

                   str_3 = str_3.substring ( 0, a );

                   str1.append ( str_3 );

              }

         } );

         return btn_4;

     }

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

     public static Node But_ton_3 ( ) {

         btn_3.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_3.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_3.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_3.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_3.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_3.setPrefWidth ( 40 );// Largura do botão

         btn_3.setLayoutX ( 130 );// Posição do botão coluna

         btn_3.setPrefHeight ( 20 );// altura do botão

         btn_3.setLayoutY ( 135 );// //Posição do botão linha

         btn_3.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   Reset ( );

                   t_0.setVisible ( false );

                   name.appendText ( "3" );

                   str_3 = "3";

                   a = str_3.length ( );

                   str_3 = str_3.substring ( 0, a );

                   str1.append ( str_3 );

              }

         } );

         return btn_3;

     }

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

     public static Node But_ton_2 ( ) {

         btn_2.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_2.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_2.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_2.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_2.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_2.setPrefWidth ( 40 );// Largura do botão

         btn_2.setLayoutX ( 82 );// Posição do botão coluna

         btn_2.setPrefHeight ( 20 );// altura do botão

         btn_2.setLayoutY ( 135 );// //Posição do botão linha

         btn_2.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   Reset ( );

                   t_0.setVisible ( false );

                   name.appendText ( "2" );

                   str_3 = "2";

                   a = str_3.length ( );

                   str_3 = str_3.substring ( 0, a );

                   str1.append ( str_3 );

              }

         } );

         return btn_2;

     }

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

     public static Node But_ton_1 ( ) {

         btn_1.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_1.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_1.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_1.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_1.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_1.setPrefWidth ( 40 );// Largura do botão

         btn_1.setLayoutX ( 32 );// Posição do botão coluna

         btn_1.setPrefHeight ( 20 );// altura do botão

         btn_1.setLayoutY ( 135 );// //Posição do botão linha

         btn_1.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   Reset ( );

                   t_0.setVisible ( false );

                   name.appendText ( "1" );

                   str_3 = "1";

                   a = str_3.length ( );

                   str_3 = str_3.substring ( 0, a );

                   str1.append ( str_3 );

              }

         } );

         return btn_1;

     }

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

     public static Node But_ton_0 ( ) {

         btn_0.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;" );

         btn_0.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_0.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;" );

              }

         } );

         btn_0.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_0.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;" );

              }

         } );

         btn_0.setPrefWidth ( 40 );// Largura do botão

         btn_0.setLayoutX ( 178 );// Posição do botão coluna

         btn_0.setPrefHeight ( 20 );// altura do botão

         btn_0.setLayoutY ( 181 );// //Posição do botão linha

         btn_0.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   //Reseta a StrinBuilder(), limpa o

                   //textfield, e reseta algumas variáveis

                   Reset ( );

                   //Apaga o zero inicial imprimido no display

                   t_0.setVisible ( false );

                   //Imprime "0" no display

                   name.appendText ( "0" );

                   str_3 = "0";

                   //Pega o tamanho da String

                   a = str_3.length ( );

                   //Apaga para não haver concatenação dos valores repetidos

                   str_3 = str_3.substring ( 0, a );

                   //A StrinBuilder() str1 Recebe a cópia da String

                   str1.append ( str_3 );

              }

         } );

         return btn_0;

     }

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

     public static Node But_ton_mais ( ) {

         btn_Rquadr.setStyle ( "-fx-font: 20 arial;"

                   + "-fx-background-color: blue;"

                   + "-fx-font-style: italic;");

         btn_Rquadr.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_Rquadr.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: red;"

                            + "-fx-font-style: italic;");

              }

         } );

         btn_Rquadr.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_Rquadr.setStyle ( "-fx-font: 20 arial;"

                            + "-fx-background-color: blue;"

                            + "-fx-font-style: italic;");

              }

         } );

         btn_Rquadr.setPrefWidth ( 282 );// Largura do botão

         btn_Rquadr.setLayoutX ( 32 );// Posição do botão coluna

         btn_Rquadr.setPrefHeight ( 20 );// altura do botão

         btn_Rquadr.setLayoutY ( 226 );// //Posição do botão linha

         btn_Rquadr.setOnAction ( new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   vet = '+';

                   //Converte StringBuilder em String

                   str_3 = str1.toString ( );

                   str1 = new StringBuilder ( );

                   //Converte a String para double

                   i = Double.parseDouble ( str_3 ); 

                   name.clear ( );

                   str1 = new StringBuilder ( );

                   fact = i;

                   for ( m = ( i - 1 ); m > 1; m-- ) {

                        fact = fact * m;

                   }            

                   str1.append ( fact );      

                   //Elimina os dois últimos caracteres da string

                   //que corresponde a: ( .0 )

                   str_2 = str1.substring ( 0, str1.length ( ) -2 );

                   // Imprime o resultado

                   // opcionalmente no console

                   System.out.println ( str_2 );

                   //Imprime o resultado no display

                   name.appendText ( " " + str_2  );   

                   t_1.setX ( 80 );//Coluna

                   t_1.setY ( 45 );//Linha

                   t_1.setText ( "Por: Samuel Lima" );

                   if ( x == true )                

                        vet = '+';                 

              }

         } );

         return btn_Rquadr;

     }

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

     public static Node But_ton_ponto ( ) {

         btn_ponto.setStyle ( "-fx-font: 20 arial;-fx-background-color: blue;");

         btn_ponto.addEventHandler ( MouseEvent.MOUSE_ENTERED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_ponto.setStyle ( "-fx-font: 20 arial;-fx-background-color: red;");

              }

         } );

         btn_ponto.addEventHandler ( MouseEvent.MOUSE_EXITED,

                   new EventHandler < MouseEvent > ( ) {

              @Override

              public void handle ( MouseEvent e ) {

                   btn_ponto.setStyle ( "-fx-font: 20 arial;-fx-background-color: blue;");

              }

         } );

         do{

              btn_ponto.setPrefWidth ( 40 );// Largura do botão

              btn_ponto.setLayoutX ( 226 );// Posição do botão coluna

              btn_ponto.setPrefHeight ( 20 );// altura do botão

              btn_ponto.setLayoutY ( 181 );// //Posição do botão linha

              //btn_ponto.setDisable ( true );

              btn_ponto.setOnAction ( new EventHandler < ActionEvent > ( ) {

                   public void handle ( ActionEvent event ) {

                        name.appendText ( "." );   

                        str_3 = ".";

                        //Pega o tamanho da String

                        a = str_3.length ( );

                        //Apaga para não haver concatenação dos valores repetidos

                        str_3 = str_3.substring ( 0, a );

                        //A StrinBuilder() str1 Recebe a cópia da String

                        str1.append ( str_3 );

                   }

              } );

              return btn_ponto;

         }while ( true );

     }

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

     public static int Text_Field ( ) {

         //Posicionamento vertical do textfield

         grid.setVgap ( 5 );

         //Posicionamento horizontal do textfield

         grid.setHgap ( 5 );

         //Tamanho máximo

         grid.setMaxSize ( 340, 440 );

         //Posicionamentos exatos do textfield

         name.setPadding ( new Insets ( 69, 20, 5, 35 ) );

         name.setTranslateX ( 31 );

         name.setTranslateY ( 19 );

         name.setAlignment ( Pos.BOTTOM_RIGHT );

         //Alguns efeitos opcionais nos textos do textfield

         name.setStyle ( "-fx-font-family: Consolas;"

                   + "-fx-font-style: italic;" + "-fx-font-size: 20px;"

                   + "-fx-base: #183308;" );

         name.setPrefColumnCount ( 21 );

         //Permite que o textfield fique todo tempo visível

         name.setVisible ( true );

         // Desliga as piscadas do cursor

         name.setEditable ( false );

         return 0;

     }

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

     @Override

     public void start ( Stage stage ) throws FileNotFoundException {

         stage.setTitle ( "JAVAFX - CALCULANDO FATORIAL" );

         Text_Field ( );

         Zero ( );

         Numeros ( );

         But_ton_0 ( );

         But_ton_1 ( );

         But_ton_2 ( );

         But_ton_3 ( );

         But_ton_4 ( );

         But_ton_5 ( );

         But_ton_6 ( );

         But_ton_7 ( );

         But_ton_8 ( );

         But_ton_9 ( );

         But_ton_del ( );

         But_ton_mais ( );

         But_ton_ponto ( );

         root.getChildren ( ).addAll ( canvas, grid, name, btn_del, btn_Rquadr,

                   btn_0, btn_1, btn_2, btn_3, btn_4, btn_5, btn_6, btn_ponto,

                   btn_7, btn_8, btn_9, t_0, t_1, t_2 );                 

         stage.setScene ( scene );

         stage.show ( );

     }

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

     public static void main ( String [ ] args ) {

         launch ( args );

     }

}