Effective Java

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ITEM 88: WRITE READOBJECT METHODS DEFENSIVELY
355
The 
byte
array literal used to initialize 
serializedForm
was generated by
serializing a normal 
Period
instance and hand-editing the resulting byte stream.
The details of the stream are unimportant to the example, but if you’re curious, the
serialization byte-stream format is described in the 
Java Object Serialization
Specification
[Serialization, 6]. If you run this program, it prints 
Fri
Jan
01
12:00:00
PST
1999
-
Sun
Jan
01
12:00:00
PST
1984
. Simply declaring 
Period
serializable enabled us to create an object that violates its class invariants.
To fix this problem, provide a 
readObject
method for 
Period
that calls
defaultReadObject
and then checks the validity of the deserialized object. If the
validity check fails, the 
readObject
method throws 
InvalidObjectException
,
preventing the deserialization from completing: