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private void writeObject(java.io.ObjectOutputStream out) 
    throws IOException;
private void readObject(java.io.ObjectInputStream in)
    throws IOException, ClassNotFoundException;
private void readObjectNoData() throws ObjectStreamException;

Wiki MarkupNote that these methods must be declared private for any serializable class. Serializable classes may also implement the {{readResolve()}} and {{writeReplace()}} methods.
According to the Serialization Specification \[ [Sun 2006|AA. References#Sun 06]\], {{readResolve()}} and {{writeReplace()}} method documentation:

For Serializable and Externalizable classes, the readResolve method allows a class to replace/resolve the object read from the stream before it is returned to the caller. By implementing the readResolve method, a class can directly control the types and instances of its own instances being deserialized.

For Serializable and Externalizable classes, the writeReplace method allows a class of an object to nominate its own replacement in the stream before the object is written. By implementing the writeReplace method, a class can directly control the types and instances of its own instances being serialized.

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Bibliography

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      13. Serialization (SER)      SER02-J. Sign then seal sensitive objects before sending them outside a trust boundary