Resumos

Per quanto riguarda il file Main.java:

package application;

public class Main {
    public static void main(String[] args) {
        MainApplication.main(args);
    }
}

Per quanto riguarda il file MainApplication.java (una sorta di main):

package application;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class MainApplication extends Application {
    @Override
    public void start(Stage primaryStage) throws Exception {
        Board board = new Board();
        Scene scene = new Scene(board);
        primaryStage.setTitle("Board");
        primaryStage.setScene(scene);
        primaryStage.setWidth(800);
        primaryStage.setHeight(800);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

Per quanto riguarda il file Board.java:

package application;

import javafx.event.EventHandler;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.input.KeyCode;
import javafx.scene.input.KeyEvent;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;

public class Board extends StackPane implements EventHandler<MouseEvent> {
    private Canvas canvas;

    public Board() {
        canvas = new Canvas();
        canvas.setOnMousePressed(this); canvas.setOnMouseDragged(this);
        canvas.setOnKeyPressed(new EventHandler<KeyEvent>() {
            @Override
            public void handle(KeyEvent event) {
                if(event.getCode().equals(KeyCode.C)) {
                    GraphicsContext graphicsContext = canvas.getGraphicsContext2D();
                    graphicsContext.clearRect(0, 0, canvas.getWidth(), canvas.getHeight());
                }
            }
        });
        canvas.setFocusTraversable(true);
        this.getChildren().add(canvas);
        canvas.widthProperty().bind(this.widthProperty());
        canvas.heightProperty().bind(this.heightProperty());
    }

    @Override
    public void handle(MouseEvent event) {
        GraphicsContext graphicsContext = canvas.getGraphicsContext2D();
        graphicsContext.setFill(Color.BLUE);
        graphicsContext.fillOval(event.getX(), event.getY(), 10, 10);
    }
}