Stuff

		field = new Field[length][length];
		for(Field[] fRow : field)
			for(Field f : fRow)
				f = new Field(4);

vs

		field = new Field[length][length];
		for(int y = 0; y < length; y++)
			for(int x = 0; x < length; x++)
				field[y][x] = new Field((y*boxWidth+x%boxWidth)%length);