java - What is the purpose of using serialVersionUID here? -

possible duplicate:
why should bother serialversionuid?

i examining struts2 validation documentation. here defined:

private static final long serialversionuid = -7505437345373234225l; 

what purpose of using serialversionuid, how use it(with random numbers?) , purpose of using @ documentation?

the serialversionuid identifier serialized objects. if serialversionuid of serialized object doesn't match current serialversionuid of class, deserialization throws invalidclassexception. uid intended changed on every structural change of class.