Lambda equation sample with JavaFX

LambdaTest.java

import java.util.Map;
import java.util.LinkedHashMap;

import static java.lang.Math.*;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import javafx.util.Duration;

public class LambdaTest extends Application {

    public static final class MyMath {
        private MyMath() {}

        public static int combination(int n, int m) {
            int ans = 1;

            for (int i = n; i > n - m; i--) {
                ans *= i;
            }

            for (int i = m; i > 0; i--) {
                ans /= i;
            }

            return ans;
        }
    }

    public static class Bezier {
        private int n;
        private double y1, y2;

        public Bezier(int n, double y1, double y2) {
            this.n = n;
            this.y1 = y1;
            this.y2 = y2;
        }

        public double calc(double t) {
            t = this.trim(t);
            double a = t;
            double b = 1 - t;
            double result = 0;

            for (int i = 0; i <= n; i++) {
                double y = getY(i);
                result += MyMath.combination(n, i) * pow(a, i) * pow(b, n - i) * y;
            }

            return result;
        }

        public double calc(double t, double max) {
            return calc(t) * max;
        }

        private double trim(double t) {
            return t > 1
                   ? 1
                   : t < 0
                     ? 0
                     : t;
        }

        protected double getY(int i) {
            return i == 0
                   ? 0
                   : i < n / 2
                     ? y1
                     : i == n
                       ? 1
                       : y2;
        }
    }
    private Map<Bezier, Rectangle> lines = new LinkedHashMap<Bezier, Rectangle>() {
        {
            Rectangle rect = new Rectangle(0, 0, 0, 0);
            rect.setFill(Color.rgb(65, 63, 158));
            this.put(new Bezier(3, 0.8, 0.75), rect);
            
            rect = new Rectangle(0, 0, 0, 0);
            rect.setFill(Color.rgb(65, 156, 152));
            this.put(new Bezier(3, 0.5, 0.5), rect);
            
            rect = new Rectangle(0, 0, 0, 0);
            rect.setFill(Color.WHITE);
            this.put(new Bezier(3, 0.2, 0.25), rect);
        }
    };
    private double t;
    
    private Scene scene;
    private Timeline timeline;

    @Override
    public void start(Stage stage) {
        stage.setTitle("Lambda Test");
        Group root = new Group();
        scene = new Scene(root, 1000, 640);
        scene.setFill(Color.BLACK);

        lines.forEach(
            (k, v) -> { 
                v.setHeight(scene.getHeight());
                root.getChildren().add(v); 
            }
        );
        
        stage.setScene(scene);
        stage.show();

        timeline = new Timeline(
            new KeyFrame(new Duration(50), e -> { this.paintBezier(); })
        );
        timeline.setCycleCount(Timeline.INDEFINITE);
        timeline.play();
    }

    public void paintBezier() {
        lines.forEach(
            (k, v) -> {
                v.setWidth(k.calc(t) * scene.getWidth());
            }
        );
 
        t += 0.005;
        if (t > 1.2) {
            timeline.stop();
        }
    }

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