Java: When to add readObjectNoData() during serialization?

Question

I am reading the serialization chapter in Effective Java. I am trying to understand the paragraph below, which is found in the book.

If you implemen

Answer 1

An invariant in your Person class could be something like:

age must be greater than 0

So, when the Person class is instantiated with the default value, 0 (see here: http://download.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html) you will have violated that invariant.

However, given the default constructor you will be fine :)