How to draw shapes gradually in canvas in javafx

Question

I want to add a sequence of points into a canvas. But the outcome is showing all points at the same time. Here is my code:

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

import java.util.Random;

public class BasicOpsTest extends Application {

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

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Drawing Operations Test");
        Group root = new Group();
        Canvas canvas = new Canvas(300, 250);
        GraphicsContext gc = canvas.getGraphicsContext2D();
        root.getChildren().add(canvas);
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
        drawShapes(gc);
    }

    private void drawShapes(GraphicsContext gc) {
        gc.setFill(Color.GREEN);
        gc.setStroke(Color.BLUE);
        Random rand = new Random();
        for (int i = 0; i < 200; i++) {
            gc.fillOval(rand.nextDouble() * 300, rand.nextDouble() * 250, 2, 2);
            try {
                Thread.sleep(10);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

I want to see the outcome adding each point successively. How can I do?

/////////// My solution using AnimationTimer is:

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.animation.AnimationTimer;

import java.util.Random;

public class BasicOpsTest extends Application {

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

    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Drawing Operations Test");
        Group root = new Group();
        Canvas canvas = new Canvas(300, 250);
        GraphicsContext gc = canvas.getGraphicsContext2D();
        root.getChildren().add(canvas);
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
        drawShapes(gc);
    }

    private void drawShapes(GraphicsContext gc) {
        Random rand = new Random();
        gc.setFill(Color.GREEN);
        AnimationTimer at = new AnimationTimer() {
            public void handle(long now) {
                gc.fillOval(rand.nextDouble() * 300, rand.nextDouble() * 250, 2, 2);
            }
        };
        at.start();
    }
}

That resolve my problem!