<hibernate-mapping>
   <class name="conf.Configuration" table="Configuration">
      <id name="id" column="CONF_ID">
         <generator class="native"/>
      </id>
      <property name="admin" type="class"/>
      <property name="technician" type="class"/>
      <property name="visitor" type="class"/>

   </class>

</hibernate-mapping>

Exception in thread "main" java.lang.ClassCastException: conf.Admin cannot be cast to java.lang.Class
   at org.hibernate.type.ClassType.toString(ClassType.java:43)
   at org.hibernate.type.NullableType.nullSafeToString(NullableType.java:93)
   at org.hibernate.type.NullableType.nullSafeSet(NullableType.java:140)
   at org.hibernate.type.NullableType.nullSafeSet(NullableType.java:107)
   at org.hibernate.persister.entity.AbstractEntityPersister.dehydrate(AbstractEntityPersister.java:2002)
   at org.hibernate.persister.entity.AbstractEntityPersister.dehydrate(AbstractEntityPersister.java:1979)
   at org.hibernate.persister.entity.AbstractEntityPersister$3.bindValues(AbstractEntityPersister.java:2157)
   at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:32)
   at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2163)
   at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2643)
   at org.hibernate.action.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:51)
   at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:279)
   at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:298)
   at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:181)
   at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:107)
   at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
   at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
   at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
   at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
   at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
   at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)
   at org.hibernate.impl.SessionImpl.save(SessionImpl.java:523)
   at org.hibernate.impl.SessionImpl.save(SessionImpl.java:519)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
   at java.lang.reflect.Method.invoke(Method.java:597)
   at org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:301)
   at $Proxy0.save(Unknown Source)