Question

Let’s say that I create an instance of class B, which has an static variable x, assigned with a value of 3 in the class B declaration. In the main() method, I do this:

B b = new B();
b.x = 7; //allowed to use an instance to set the static member value

After this, b is serialized and then de-serialized. Then, the following line occurs:

System.out.println ("static: " + b.x);

What’s the value? 7 or 3?

I know static variables are not serialized, however, since there is only one copy of the static member for the whole class, and the value is set to 7, should it be preserved after de-serializing an instance?

Answer 1

Here’s what happens:

1. Static initializer sets the value to 3.
2. Instance constructor sets the value to 7.
3. Serialization is unaware of the static variable and it is ignored.
4. De-serialization is unaware of static variable and it is ignored.
5. Value is still 7 (from the change that occurred in the constructor) if the program has been running all along, or if the program was shutdown and restarted, the static initializer will have set it to 3 and de-serialization did not change it.

If you want the logic you describe, you need to add another static variable which counts the number of instances created and override the writeObject and readObject methods with your custom logic.