empCodeKeyAndLineValueMapcomputeIfAbsentempCode k - new ArrayListaddlineNum; 使用 putIfAbsent 并判断不为空

empCodeKeyAndLineValueMap.putIfAbsent(empCode, new ArrayList<>()); if (empCodeKeyAndLineValueMap.get(empCode) != null) { empCodeKeyAndLineValueMap.get(empCode).add(lineNum); }