JavaFx - Imprimindo valores em TextArea

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Veja abaixo o código do programa:

import javafx.scene.Scene;

import javafx.scene.control.TextArea;

import javafx.stage.Stage;

import javafx.application.Application;

import javafx.geometry.Insets;

import javafx.scene.layout.GridPane;

import javafx.scene.layout.VBox;

import javafx.scene.layout.BorderPane;

import javafx.scene.canvas.Canvas;

import javafx.scene.canvas.GraphicsContext;

import javafx.scene.layout.Pane;

import javafx.event.ActionEvent;

import javafx.scene.Group;

import javafx.scene.Node;

import javafx.scene.control.Button;

import javafx.event.EventHandler;

import javafx.scene.paint.Color;

import javafx.scene.control.Menu;

import javafx.scene.control.MenuBar;

import javafx.scene.control.MenuItem;

import javafx.scene.text.Font;

import javafx.scene.text.FontWeight;

import javafx.scene.text.Text;

import javafx.concurrent.Task;

public class PROJETO extends Application {

     static String str_2 = "MUITO OBRIGADO";

     static String str_1 = "Por: Samuel Lima";

     static String str = new String ( );

     static String str_3 = new String ( );

     static String str_4 = "";

     static String str_5 = "";

     static Button btn_1 = new Button ( "Inf" );

     static Button btn_2 = new Button ( "Cls" );

    static Text t_0 = new Text ( );

    static Text t_1 = new Text ( );

    static Text t_2 = new Text ( );

     static Text t_3 = new Text ( );

     static Text t_4 = new Text ( );

     static Group g = new Group ( );

     static Canvas canvas = new Canvas (  );

     static GraphicsContext ctx = canvas.getGraphicsContext2D ( );

     static TextArea    text          = new TextArea ( );   

     static VBox vbox = new VBox ( );

     static GridPane grid = new GridPane ( ); 

     static MenuBar menuBar = new MenuBar ( );

     static Pane ro_ot = new Pane ( );

     static BorderPane root = new BorderPane ( );

     static Scene scene = new Scene ( vbox, 500, 500 );

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

     public static void TextString ( ) {

         t_0.setFont ( Font.font ( "Arial", FontWeight.BOLD, 25 ) );

         t_1.setFont ( Font.font ( null, FontWeight.BOLD, 15 ) );

         t_2.setFont ( Font.font ( "Arial", FontWeight.NORMAL, 25 ) );

     }

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

     public static Node But_ton_1 ( ) {

         btn_1.setPrefWidth ( 50 );// Largura do botão

         btn_1.setLayoutX ( 29 );// Posição do botão coluna

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

         btn_1.setLayoutY ( 40 );// //Posição do botão linha

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

              @Override

              public void handle ( ActionEvent event ) {

                   int b = 0;

                   b = 1;

                   Sleep ( 1800, b );

                   b = 2;

                   Sleep ( 2800, b );

              }

         } );

         ro_ot.getChildren ( ).add ( btn_1 );

         return btn_1;

     }

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

     private static Node But_ton_2 ( ) {

         btn_2 .setPrefWidth ( 50 );// Largura do botão

         btn_2.setLayoutX ( 357 );// Posição do botão coluna

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

         btn_2 .setLayoutY ( 40 );// //Posição do botão linha

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

              @Override

              public void handle ( ActionEvent event ) {

                   // Coluna, linha, comprimento, altura

                   // Apagando uma linha ou partes

                   ctx.clearRect ( 80, 120, 180, 80 );

                   t_2.setVisible( false );

                   t_3.setVisible( false );

                   btn_1.setVisible ( false );

                   btn_2.setVisible ( false );

              }

         } );

         ro_ot.getChildren ( ).add ( btn_2 );

         return btn_2;

     }

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

     // Chamando uma função depois de um certo tempo

     public static void Tempo_2 ( ) {

         t_3.setFont ( Font.font ( null, FontWeight.BOLD, 15 ) );

         t_3.setX ( 110 );

         t_3.setY ( 130 );

         t_3.setFill ( Color.BLUE );

         t_3.setText ( str_2 );

         root.getChildren ( ).add ( t_3 );

     }

     public static void Tempo_1 ( ) {

         t_2.setFont ( Font.font ( null, FontWeight.BOLD, 15 ) );

         t_2.setX ( 110 );

         t_2.setY ( 110 );

         t_2.setFill ( Color.RED );

         t_2.setText ( str_1 );

         root.getChildren ( ).add ( t_2 );

     }

     public static int Sleep ( int x, int k ) {

         Task < Integer > close = new Task < Integer > ( ) {

              @Override

              protected Integer call ( ) throws Exception {

                   Thread.sleep ( x );

                   return null;

              }

         };

         close.setOnSucceeded ( c -> {

              if ( k == 1 )

                   Tempo_1 ( );

              if ( k == 2 )

                   Tempo_2 ( );

         } );

         new Thread ( close ).start ( );

         return 0;

     }

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

     public static int Menu_Bar ( ) {

         EventHandler < ActionEvent > action = changeTabPlacement ( );

         Menu menu = new Menu ( "Arq" );

         MenuItem top = new MenuItem ( "Exit" );

         top.setOnAction ( action );

         menu.getItems ( ).add ( top );

         MenuItem bottom = new MenuItem ( "Inf" );

         bottom.setOnAction ( action );

         menu.getItems ( ).add ( bottom );

         menuBar.getMenus ( ).add ( menu );

         root.setTop ( menuBar );

         return 0;

     }

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

     private static EventHandler < ActionEvent > changeTabPlacement ( ) {

         return new EventHandler < ActionEvent > ( ) {

              public void handle ( ActionEvent event ) {

                   MenuItem mItem = ( MenuItem ) event.getSource ( );

                   String side = mItem.getText ( );

                   if ( "Exit".equalsIgnoreCase ( side ) ) {

                        System.exit ( 0 );

                   } else if ( "Inf".equalsIgnoreCase ( side ) ) {

                        But_ton_1 ( );

                        But_ton_2 ( );

                   }

              }

         };

     }

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

     static float Inte_iro ( double x ) {

         int inteiro = 0;

         inteiro = ( int ) x;

         if ( x == inteiro ) {

              return 1;

         } else {

              return 0;

         }

     }

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

     public static int Text_Area ( ){

         TextString ( );

         t_1.setX ( 60 );

         t_1.setY ( 50 );

         t_1.setFill ( Color.RED );

         t_1.setText ( "IMPRIMINDO VALORES EM TEXTAREA JAVAFX" );

         double x = 12.5;

         double y = 12;

         // Para números decimais

         if ( Inte_iro ( x ) == 0 ) {

              //System.out.println ( Math.sqrt ( x ) );

              str += Math.sqrt ( x );

         }        

         // Para números inteiros

         if ( Inte_iro ( y ) == 1 ) {

              //System.out.println ( Math.sqrt ( y ) );

              str_3 += Math.sqrt ( y );

         }

         text.setFont ( Font.font("Amble Cn", FontWeight.BOLD, 25 ) );

         text.appendText ( "Abaixo a raiz quadrada de => " );

         text.appendText ( "" + x + "\n" );

         text.appendText ( str );

         text.appendText ( "\nAbaixo a raiz quadrada de => " );

         text.appendText ( "" + y + "\n" );

         text.appendText ( str_3 );

         grid.setVgap ( 4 );

         grid.setHgap ( 2 );   

         root.setPadding ( new Insets ( 1, 1, 1, 1 ) );

         //Posiciona a Margem do TextArea

         grid.add ( text, 1, 20, 2, 10 );

         root.setMinWidth ( 150 );

         text.setStyle ( "-fx-font-style: italic;"

                   + " -fx-font-weight: bolder;"

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

                   +  "-fx-alignment: center;"

                   + "-fx-text-fill: blue" );

         root.getChildren ( ).addAll ( grid, t_1, t_4 );

         return 0;

     }

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

     @Override

     public void start ( Stage stage ) throws Exception {

         stage.setTitle ( "IMPRIMINDO VALORES EM TEXTAREA JAVAFX" );

         Menu_Bar ( );

         // Dando uns efeitos na moldura

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

                   + "-fx-border-width: 18;" + "-fx-border-insets: 5;"

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

         Text_Area ( );

         vbox.getChildren ( ).addAll ( canvas, root, ro_ot, grid );

         stage.setScene ( scene );

         stage.show ( );

     }

     public static void main ( String [ ] args ) {

         launch ( args );

     }

}