I was trying this way, but it doesn't work (no exception is thrown, MDR event is
fired, but nth changes in the editor):

JavaClass serializableInterface = (JavaClass)
JavaModel.getDefaultExtent().getType().resolve("java.io.Serializable");
javaClass.getInterfaces().add(serializableInterface);


Now I am using the following work-around code instead:

MultipartIdClass idProxy =
((JavaModelPackage)javaClass.refImmediatePackage()).getMultipartId();
MultipartId id = idProxy.createMultipartId("java.io.Serializable", null, null);
javaClass.getInterfaceNames().add(id);


Complete example can be found in the
org.netbeans.modules.j2ee.verification.presistence.hints.ImplementSerializableHint
class (release55 branch)