public void addZombies(GameContainer gc, int delta) throws SlickException {
		timeZombie -= delta;
		if (zombies.size() == 0 && timeZombie <= 0) {
			for (int i = 0; i < this.Walker; i++) {
				ZombieAppearSound.play();
				randomZombieX();
				zombies.add(new Zombies(ZombiePositionX, -100));
			}
			this.Walker += 3;
			if (Walker > 3) {
				for (int j = 0; j < this.Walker-3; j++) {
					ZombieAppearSound.play();
					randomZombieX();
				zombies.add(new FastZombies(ZombiePositionX, -100));
				}
			}
			if (Walker > 10) {
				for (int j = 0; j < this.Walker-9; j++) {
					ZombieAppearSound.play();
					randomZombieX();
				zombies.add(new DieHardZombies(ZombiePositionX, -100));
				}
			}
			timeZombie = default_zombie_delay;
		}
	}