Question

Suppose I serialize the below class (by putting a value to field x, say 5), and before doing the deserialization, I remove field x and put a new field y (int or float), what will be the result?

I believe deserialization is done successfully and value of field y will be default, is this correct?

If this is correct, where will the value if x will go in the transition from persistent object to stateful object at serialization time?

public class Cat implements Serializable{    
  private static final long serialVersionUID = 4231235177539824282L;  
  int x;
}

before deserialization:

public class Cat implements Serializable{    
  private static final long serialVersionUID = 4231235177539824282L;  
  float/int y;
}

Answer 1

The serialization spec details the inner workings of field deserialization (you can find it here: http://docs.oracle.com/javase/7/docs/platform/serialization/spec/input.html)

If you browse through the “readObject method” section it states:

Any field of the object that does not appear in the stream is set to
its default value. Values that appear in the stream, but not in the
object, are discarded. This occurs primarily when a later version of a
class has written additional fields that do not occur in the earlier
version.

So in essence, the field ‘x’ will have some value in the stream, but will be discarded and the field ‘y’ will be set to 0 (default value) since it does not appear in the stream.