FlappyTurtle/Welt.java

import java.util.ArrayList;
import java.util.Random;

class Welt implements Drawable
{
    private static final int DISTANCE = 250;
    private final ArrayList<Rectangle> _obstacles;
    private double _speed = 150;
    private double _acc = 0.5;
    private final Random _random;

    public Welt(Manager manager)
    {
        manager.addDrawable(this);
        _random = new Random();
        _obstacles = new ArrayList<Rectangle>();
        reset();
    }

    public void reset()
    {
        _obstacles.clear();
        createObstacle(TurtleWelt.WIDTH);
    }

    private void createObstacle(int x)
    {
        int gap = _random.nextInt(TurtleWelt.HEIGHT - 200) + 50;
        _obstacles.add(new Rectangle(x, 0, 30, gap, "black", false));
        _obstacles.add(new Rectangle(x, gap + 100, 30, TurtleWelt.HEIGHT, "black", false));
    }

    public void update(double elapsed)
    {
        ArrayList<Rectangle> remove = new ArrayList<Rectangle>();
        for (Rectangle r : _obstacles)
        {
            // Move all obstacles accoring to speed
            r.setPos(r.getX() - (elapsed * 1e-3 * _speed), r.getY());

            // Mark obstacles that are off screen for removal to avoid
            // concurrent modifications
            if (r.getX() < -r.getWidth())
            {
                remove.add(r);
            }
        }
        for (Rectangle r : remove)
        {
            _obstacles.remove(r);
        }

        // Add a new obstacle after DISTANCE
        Rectangle lastObstacle = _obstacles.get(_obstacles.size() - 1);
        if (lastObstacle.getX() + lastObstacle.getWidth() < TurtleWelt.WIDTH - DISTANCE)
        {
            createObstacle(TurtleWelt.WIDTH);
        }

        // Increase speed according to acceleration
        _speed += _acc * elapsed * 1e-3;
    }

    public boolean checkCollision(Rectangle r)
    {
        for (Rectangle o : _obstacles)
        {
            if (r.intersects(o))
            {
                return true;
            }
        }
        return false;
    }

    public void draw(Turtle t, double elapsed)
    {
        for (Rectangle r : _obstacles)
        {
            if (r.getX() < TurtleWelt.WIDTH)
            {
                r.draw(t, elapsed);
            }
        }
    }
}