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if you serialize a singleton object and subsequently deserialize that object more than once, you will have multiple singleton instances.It beats the purpose and hence.

Regarding cloneable, obvious - it allows the singleton to be cloned -again - not desirable.

I guess Serialization ignores static fields, because they are not part of any particular object state..And in singleton classes, we use a static variable to keep the only instance of the class..So it maybe a problem..

Thanks for the details Ji and Garry...Just to summarize..so that it can help others.

Singlton => One instance of a class.

If you make the class implements serializable then there could be more instance of class that gets created during deserialization if called twice or used reset() methods on the stream. Similarly while serializing it can cause problem if serialization chain in broken or reset() is called during serialization.

And as static fields are not part of serialization, and it plays very important role in singleton there could be a problem of loosing the value.

Cloneable => If we call cloneable on the object then it would generate the another object hence returning another instance of a class.