应用程序中的每个Java类都需要具有不同的唯一串行版本ID吗？

Question

From I read online, it seems a good practice to create a serial version ID for a class.

My question is that in an application, do I have to create an unique ID for each class?

Or can I simply assign the following ID to each class in my application?

private static final long serialVersionUID = 1;

Answer 1

• You only need a serial version ID for classes that will be serialized, ie mostly those that implement Serializable
• The ID is per class, it's not a problem if two classes have the same
• It's only necessary if there is a chance that serialized instances will be deserialized by a different version of the program. This is often not the case.

Answer 2

No, it doesn't matter what the ID is for the specific class - it's the serialization format version for that class . The class name itself is still serialized, so it's not like it has to be unique across all classes. (Of course, you may find other ways in which having a different version number for each class would be useful. I can't think of any off hand, but that's a different matter.)

Using a constant value is fine - but you do need to make sure you change it when you've genuinely changed the serialization format (eg by adding a field).

Mind you, I'd prefer to use something like Protocol Buffers which is rather more graceful with backward/forward compatibility :)