placeAlien

    /**
     * At level 2 an alien ship appears a few seconds into the level. It follows
     * a zig-zag path, periodically firing bullets in random directions. When it
     * is destroyed, you earn 200 points. A few seconds later, it appears again.
     */
    private void placeAlien() {
        Participant.expire(this.alien);
        if (this.level > 1) {
            int alienShipSize = this.level == 2 ? 1 : 0;
            this.alien = new Alien(alienShipSize, this);
            this.alien
                    .setPosition(0.0D, 750.0D * Constants.RANDOM.nextDouble());
            this.alien.setVelocity(5 - alienShipSize,
                    Constants.RANDOM.nextInt(2) * 3.141592653589793D);
            addParticipant(this.alien);
        }
    }