What is the purpose of using serialVersionUID here? [duplicate]

Question

Possible Duplicate:
Why should I bother about serialVersionUID?

I was examining the Struts2 validation documentation. Even here it is defined:

private static final long serialVersionUID = -7505437345373234225L;

What is the purpose of using serialVersionUID, how to use it(with random numbers?) and what is the purpose of using it at that documentation?

Answer 1

The serialVersionUID is an identifier for serialized objects. If the serialVersionUID of a serialized object doesn't match to the current serialVersionUID of that class, then the deserialization throws an InvalidClassException. The UID is intended to be changed on every structural change of a class.