FULL PRODUCT VERSION :
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Darwin Wessels-MacBook-Pro.local 14.3.0 Darwin Kernel Version 14.3.0: Mon Mar 23 11:59:05 PDT 2015; root:xnu-2782.20.48~5/RELEASE_X86_64 x86_64

But I think all OSes are affected.

A DESCRIPTION OF THE PROBLEM :
Externalizable says:

When an Externalizable object is reconstructed, an instance is created using the public no-arg constructor, then the readExternal method called. Serializable objects are restored by reading them from an ObjectInputStream.

But the ActivationDataFlavor does not have a public no-arg constructor. Which results in errors when trying to read from an ObjectInputStream.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Try to deserialize an ActivationDataFlavor object and see that it works/fails.



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I would expect that deserialization of the object works so that my example class would output:

This should say true: true
ACTUAL -
Exception in thread "main" java.io.InvalidClassException: javax.activation.ActivationDataFlavor; no valid constructor
at java.io.ObjectStreamClass$ExceptionInfo.newInvalidClassException(ObjectStreamClass.java:150)
at java.io.ObjectStreamClass.checkDeserialize(ObjectStreamClass.java:768)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1775)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
at ActivationDataFlavorBug.main(ActivationDataFlavorBug.java:23)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

import javax.activation.ActivationDataFlavor;

public class ActivationDataFlavorBug {
  public static void main(String[] args) throws Exception {
    File tempFile = null;
    try {
      tempFile = File.createTempFile("activationDataFlavorBug", "outputStream");
      ActivationDataFlavor activationDataFlavor = new ActivationDataFlavor("application/text", "text");
      FileOutputStream fileOutputStream = new FileOutputStream(tempFile);
      ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
      objectOutputStream.writeObject(activationDataFlavor);
      objectOutputStream.close();
      fileOutputStream.close();
      FileInputStream fileInputStream = new FileInputStream(tempFile);
      ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
      Object readObject = objectInputStream.readObject();
      System.out.println("This should say true: " + (readObject instanceof ActivationDataFlavor));
      objectInputStream.close();
      fileInputStream.close();
    } finally {
      if (tempFile != null && tempFile.exists()) {
        tempFile.delete();
      }
    }
  }
}

---------- END SOURCE ----------