public void addBuilding(BuildingModel building, int x, int y)
			throws GameFieldException {
		if (!checkPosition(x, y)) {
			throw new GameFieldException(String.format(
					"Accesing square with invalid position (%d, %d).", x, y));
		}
		switch (map[y][x]) {
		case GRASS:
			buildings[y][x] = building;
			break;
		case MOUNTAIN:
		case WATER:
			throw new GameFieldException("Adding to not invalid square");
		}

	}