final transient fields and serialization
- by doublep
Is it possible to have final transient fields that are set to any non-default value after serialization in Java? My usecase is a cache variable — that's why it is transient. I also have a habit of making Map fields that won't be changed (i.e. contents of the map is changed, but object itself remains the same) final. However, these attributes seem to be contradictory — while compiler allows such a combination, I cannot have the field set to anything but null after unserialization.
I tried the following, without success:
simple field initialization (shown in the example): this is what I normally do, but the initialization doesn't seem to happen after unserialization;
initialization in constructor (I believe this is semantically the same as above though);
assigning the field in readObject() — cannot be done since the field is final.
In the example cache is public only for testing.
import java.io.*;
import java.util.*;
public class test
{
public static void main (String[] args) throws Exception
{
X x = new X ();
System.out.println (x + " " + x.cache);
ByteArrayOutputStream buffer = new ByteArrayOutputStream ();
new ObjectOutputStream (buffer).writeObject (x);
x = (X) new ObjectInputStream (new ByteArrayInputStream (buffer.toByteArray ())).readObject ();
System.out.println (x + " " + x.cache);
}
public static class X implements Serializable
{
public final transient Map <Object, Object> cache = new HashMap <Object, Object> ();
}
}
Output:
test$X@1a46e30 {}
test$X@190d11 null
