Serialisation - readObject and writeObject

 what is the significance of readObject and writeObject method in Serialization ?

These methods are not declared in any class or interface. A class, that implements the Serializableinterface and requires special special handling during the serialization and deserialization process must implement those methods and the serializer/deserializer will try to reflect those methods.

 These methods are (and must be) declared private (when implementing your own), proving/indicating that neither method is inherited and overridden or overloaded by the implementation. The trick here is that the JVM automatically checks to see if either method is declared during the corresponding method call. Note that the JVM can call private methods of your class whenever it wants but no other objects can. Thus, the integrity of the class is maintained and the serialization protocol can continue to work as normal.