JavaFX - abrindo janelas

Poder abrir novas janelas é fundamental
para programas mais complexo,
Aqui eu mostro um exemplo em JavaFX
de como isto pode ser feito.
Veja abaixo imagens do programa em execução: 

Veja abaixo um vídeo com o funcionamento do programa:

                                                   
Veja abaixo o código do programa:   

import javafx.application.Application;

import javafx.stage.Stage;

import javafx.scene.Scene;

import javafx.scene.canvas.Canvas;

import javafx.scene.canvas.GraphicsContext;

import javafx.scene.paint.Color;

import javafx.scene.text.Font;

import javafx.scene.text.FontWeight;

import javafx.event.ActionEvent;

import javafx.event.EventHandler;

import javafx.scene.control.Menu;

import javafx.scene.control.MenuBar;

import javafx.scene.control.MenuItem;

import javafx.scene.layout.BorderPane;

import javafx.scene.input.KeyCodeCombination;

import javafx.scene.input.KeyCombination;

import javafx.scene.input.KeyCode;

class Janela_3 {

     PROJETO pro = new PROJETO ( );

     BorderPane root = new BorderPane ( );

     Scene scene = new Scene ( root, 500, 300 );

     Canvas canvas = new Canvas ( 500, 300 );

     GraphicsContext ctx = canvas.getGraphicsContext2D ( );

     MenuBar menubar = new MenuBar ( );

     Menu menu = new Menu ( "Arq" );

     MenuItem exit = new MenuItem ( "Sair" );

     MenuItem jan_1 = new MenuItem ( "Janela_1" );

     MenuItem jan_2 = new MenuItem ( "Janela_2" );

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

     public void Menu ( Stage stage ) {

         menu.getItems ( ).addAll ( jan_1, jan_2, exit );

         menubar.getMenus ( ).add ( menu );

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

              @Override

              public void handle ( ActionEvent e ) {

                   stage.close ( );

              }

         } );

         jan_1.setOnAction ( new EventHandler < ActionEvent > ( ) {

              @Override

              public void handle ( ActionEvent e ) {

                   pro.start ( stage );

              }

         } );

         jan_2.setOnAction ( new EventHandler < ActionEvent > ( ) {

              @Override

              public void handle ( ActionEvent e ) {

                   new Janela_2 ( stage );

              }

         } );

         exit.setAccelerator ( new KeyCodeCombination ( KeyCode.E,

                   KeyCombination.CONTROL_DOWN ) );

         jan_1.setAccelerator ( new KeyCodeCombination ( KeyCode.C,

                   KeyCombination.CONTROL_DOWN ) );

         jan_2.setAccelerator ( new KeyCodeCombination ( KeyCode.D,

                   KeyCombination.CONTROL_DOWN ) );

     }

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

     Janela_3 ( Stage stage ) {

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

         ctx.setFill ( Color.RED );

         ctx.fillText ( "JAVAFX - TERCEIRA JANELA", 150, 80 );

         // Criando uma moldura na janela

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

                   + "-fx-border-width: 10;" + "-fx-border-insets: 5;"

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

         Menu ( stage );

         pro.Informe ( ctx );

         root.getChildren ( ).add ( canvas );

         root.setTop ( menubar );

         stage.setScene ( scene );

         stage.show ( );

     }

}

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

class Janela_2 {

     PROJETO pro = new PROJETO ( );

     BorderPane root = new BorderPane ( );

     Scene scene = new Scene ( root, 500, 300 );

     Canvas canvas = new Canvas ( 500, 300 );

     GraphicsContext ctx = canvas.getGraphicsContext2D ( );

     MenuBar menubar = new MenuBar ( );

     Menu menu = new Menu ( "Arq" );

     MenuItem exit = new MenuItem ( "Sair" );

     MenuItem jan_1 = new MenuItem ( "Janela_1" );

     MenuItem jan_3 = new MenuItem ( "Janela_3" );

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

     public void Menu ( Stage stage ) {

         menu.getItems ( ).addAll ( jan_1, jan_3, exit );

         menubar.getMenus ( ).add ( menu );

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

              @Override

              public void handle ( ActionEvent e ) {

                   stage.close ( );

              }

         } );

         jan_1.setOnAction ( new EventHandler < ActionEvent > ( ) {

              @Override

              public void handle ( ActionEvent e ) {

                   pro.start ( stage );

              }

         } );

         jan_3.setOnAction ( new EventHandler < ActionEvent > ( ) {

              @Override

              public void handle ( ActionEvent e ) {

                   new Janela_3 ( stage );

              }

         } );

         exit.setAccelerator ( new KeyCodeCombination ( KeyCode.E,

                   KeyCombination.CONTROL_DOWN ) );

         jan_1.setAccelerator ( new KeyCodeCombination ( KeyCode.C,

                   KeyCombination.CONTROL_DOWN ) );

         jan_3.setAccelerator ( new KeyCodeCombination ( KeyCode.D,

                   KeyCombination.CONTROL_DOWN ) );

     }

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

     Janela_2 ( Stage stage ) {

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

         ctx.setFill ( Color.RED );

         ctx.fillText ( "JAVAFX - SGUNDA JANELA", 150, 80 );

         // Criando uma moldura na janela

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

                   + "-fx-border-width: 10;" + "-fx-border-insets: 5;"

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

         Menu ( stage );

         pro.Informe ( ctx );

         root.getChildren ( ).add ( canvas );

         root.setTop ( menubar );

         stage.setScene ( scene );

         stage.show ( );

     }

}

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

public class PROJETO extends Application {

     public Canvas canvas = new Canvas ( 500, 300 );

     public GraphicsContext ctx = canvas.getGraphicsContext2D ( );

     BorderPane root = new BorderPane ( );

     Scene scene = new Scene ( root, 500, 300 );

     MenuBar menubar = new MenuBar ( );

     Menu menu = new Menu ( "Arq" );

     MenuItem exit = new MenuItem ( "Sair" );

     MenuItem jan_2 = new MenuItem ( "Janela_2" );

     MenuItem jan_3 = new MenuItem ( "Janela_3" );

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

     public void Informe ( GraphicsContext ctx ) {      

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

         ctx.setFill ( Color.RED );

         ctx.fillText ( "Por: ", 180, 235 );

         ctx.setFill ( Color.BLUE );

         ctx.fillText ( "Samuel Lima", 210, 235 );

         ctx.setFill ( Color.BLACK );

         ctx.fillText ( "sa_sp10@hotmail.com", 180, 250 );

         ctx.setFill ( Color.RED );

         ctx.fillText ( " MUITO OBRIGADO", 200, 275 );

     }

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

     public void Menu ( Stage stage ) {

         menu.getItems ( ).addAll ( jan_2, jan_3, exit );

         menubar.getMenus ( ).add ( menu );

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

              @Override

              public void handle ( ActionEvent e ) {

                   stage.close ( );

              }

         } );

         jan_2.setOnAction ( new EventHandler < ActionEvent > ( ) {

              @Override

              public void handle ( ActionEvent e ) {

                   new Janela_2 ( stage );

              }

         } );

         jan_3.setOnAction ( new EventHandler < ActionEvent > ( ) {

              @Override

              public void handle ( ActionEvent e ) {

                   new Janela_3 ( stage );

              }

         } );

         exit.setAccelerator ( new KeyCodeCombination ( KeyCode.E,

                   KeyCombination.CONTROL_DOWN ) );

         jan_2.setAccelerator ( new KeyCodeCombination ( KeyCode.C,

                   KeyCombination.CONTROL_DOWN ) );

         jan_3.setAccelerator ( new KeyCodeCombination ( KeyCode.D,

                   KeyCombination.CONTROL_DOWN ) );

     }

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

     public void start ( Stage stage ) {

         stage.setTitle ( "JAVAFX - ABRINDO JANELAS" );

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

         ctx.setFill ( Color.RED );

         ctx.fillText ( "JAVAFX - PRIMEIRA JANELA", 150, 80 );

         // Criando uma moldura no texarea

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

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

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

         Menu ( stage );

         Informe ( ctx );

         root.getChildren ( ).add ( canvas );

         root.setTop ( menubar );

         stage.setScene ( scene );

         stage.show ( );

     }

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

     public static void main ( String [ ] args ) {

         Application.launch ( args );

     }

}