what happens when try to serialize static variable

[Wil Guo]

This is the question from K&B book

import java.io.*;
 
public class TestSer {
  public static void main(String[] args) {
    SpecialSerial s = new SpecialSerial();
    try {
      ObjectOutputStream os = new ObjectOutputStream(
                 new FileOutputStream("myFile"));
      os.writeObject(s); os.close();
 
      System.out.print(++s.z + " ");
      ObjectInputStream is = new ObjectInputStream(
                 new FileInputStream("myFile"));
      SpecialSerial s2 = (SpecialSerial)is.readObject();
      is.close();
      System.out.println(s2.y + " " + s2.z);
    } catch (Exception x) {System.out.println("exc"); }
  }
}
 
class SpecialSerial implements Serializable {
  transient int y = 7;
  static int z = 9;
}

Output would be: 10 0 10

Can anyone explain why s2.z would give 10? What is the result when trying to serialize and deserialize static variable?

Thanks!



[HENRY: Formatted Code]
[ December 11, 2006: Message edited by: Henry Wong ]

[Henry Wong]

Output would be: 10 0 10

Can anyone explain why s2.z would give 10? What is the result when trying to serialize and deserialize static variable?

Static variables do not get serialized or deserialized -- the value of s2.z is equal to 10, because it is equal to 10. Deserialization does not change it. If you set s.z to 3 prior to deserialization, you'll notice that s2.z is also 3 after deserialization.

Henry
[ December 11, 2006: Message edited by: Henry Wong ]

[Burkhard Hassel]

Hi ranchers,

note the difference between static and transient variables:
A transient variable is set to the default value (null, 0, 0.0) after deserialization.
Static variables, belonging to the class, are not changed at all.

It is also possible to have a variable that is both, static and transient. It is nonsense, but it compiles. And it behaves as if you made it just static (without the transient modifier).

Yours,
Bu.