java.io.InvalidClassException: local class incompatible:

Question

I created client and server and then added a class in client side for serializing purposes, then simply just went to the folder of the client in my hard drive and copy paste

Answer 1

The exception message clearly speaks that the class versions, which would include the class meta data as well, has changed over time. In other words, the class structure during serialization is not the same during de-serialization. This is what is most probably "going on".