This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Think about it this way, since the Parent is not Serializable, then the inherited variables from the parent are not saved when the child object is serialized. So in that case, when the child is de-serialized, those inherited variables need to be reset to their default values and their no-args constructor is called.