两个ArrayList复杂了，一个ArrayList就可以了，队首的话用index = 0就可以指定队首。 public static void main(String[] args) { Scanner in = new Scanner(System.in); int n = Integer.parseInt(in.nextLine().trim()); ArrayList<string> arr = new ArrayList<>(); int index = 0; for (int i = 0; i < n; i++) { String[] s = in.nextLine().split(" "); if ("push".equals(s[0])){ arr.add(s[1]); } else if ("pop".equals(s[0])) { if (arr.isEmpty()){ System.out.println("error"); continue; } System.out.println(arr.remove(index)); } else if ("front".equals(s[0])) { if (arr.isEmpty()){ System.out.println("error"); continue; } System.out.println(arr.get(index)); } } }</string>