Serializing a Scala class that extends a Java class: value lost?
java, scala, serialization
Solution
This is expected and I believe has nothing to do with Scala. Non-Serializable superclasses are not serialized out (as they are not serializable!) and thus their values will be initialized by the default constructor.
If you want to somehow save the superclass, you'll need to override your readObject and writeObject to save the state manually. Or, use a more flexible serialization solution that writes XML, JSON, etc. and uses reflection.
Problem
Foo.java ``` public class Foo{ public int i = 0; } ``` Bar.scala ``` class Bar() extends Foo with Serializable{ i = 1 } ``` Serialization via Josh Seureth https://stackoverflow.com/a/3442574/390708 ``` import java.io._ class Serialization{ def write(x : AnyRef) { val output = new ObjectOutputStream(new FileOutputStream("test.obj")) output.writeObject(x) output.close() } def read[A] = { val input = new ObjectInputStream(new FileInputStream("test.obj")) val obj = input.readObject() input.close() obj.asInstanceOf[A] } } ``` REPL session, bar is 1 before serialization but 0 after. ``` scala -cp . Welcome to Scala version 2.9.1.final (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_03). Type in expressions to have them evaluated. Type :help for more information. scala> val bar = new Bar bar: Bar = Bar@2d2ab673 scala> bar.i res0: Int = 1 scala> :load Serialization.scala Loading Serialization.scala... import java.io._ defined class Serialization scala> val serialization = new Serialization serial: Serialization = Serialization@41a45f89 scala> serialization.write(bar) scala> val bars = serialization.read[Bar] bars: Bar = Bar@5a9948fd scala> bars.i res3: Int = 0 ``` So, why isn't bars.i 1 in this case?