Java in a Nutshell, 5th Edition [Electronic resources]

Thrown by the readObject( ) method of an ObjectInputStream when it encounters primitive type data where it expects object data. Despite the exception name, this data is not optional, and object deserialization is stopped.

public class 
OptionalDataException  extends ObjectStreamException {
// No Constructor
// Public Instance Fields
public boolean 
eof ;  
public int 
length ;  
}