不建议用GetHashCode做Object唯一标识（官方）
- You should not assume that equal hash codes imply object equality.
- You should never persist or use a hash code outside the application domain in which it was created, because the same object may hash across application domains, processes, and platforms.
不建议使用ArrayList类，建议使用泛型 List 类
ArrayList类旨在保存对象的异类集合。 但是，它并不总是提供最佳性能。