参考答案
结论：用Collections.synchronizedList、Vector或CopyOnWriteArrayList，或手动同步。原理：synchronizedList包装后方法级加锁，适合低并发；Vector方法加synchronized但锁粗效率低已过时；CopyOnWriteArrayList写时复制新数组，读无锁适合读多写少；对比写频繁用外部synchronized(list){list.add()}避免ConcurrentModificationException。示例：List l = Collections.synchronizedList(new ArrayList<>());