JMX as integrated into J2SE should use generics in its interfaces.
Through the magic of type erasure this should not affect portability
of JMX client code to standalone JMX 1.2.

Here is a possibly incomplete list of changes:

MBeanServer[Connection].queryMBeans should return Set<ObjectInstance>.
MBeanServer[Connection].queryNames should return Set<ObjectName>.
AttributeChangeNotificationFilter.getEnabledAttributes should return Vector<String>.
AttributeList should extend ArrayList<Attribute>.
MBeanServerFactory.findMBeanServer should return ArrayList<MBeanServer>.
NotificationFilterSupport.getEnabledTypes should return Vector<String>.
ObjectName's constructor and getInstance method that take a Hashtable should take a Hashtable<String,String>.
ObjectName.getKeyPropertyList should return Hashtable<String,String>.
MLetMBean and MLet's methods getMBeansFromURL cannot use generics because the elements of the returned Set can be either ObjectInstance or Throwable.
CompositeType.keySet should return Set<String>.
Not sure about some other keySet methods in openmbean package.
TabularType.getIndexNames should return List<String>.
Relation.getReferencedMBeans should return Map<ObjectName,ArrayList<String>>.
In RelationServiceMBean:
- findAssociatedMBeans returns Map<ObjectName,ArrayList<String>>.
- findRelationsOfType returns List<String>.
- getRole returns List<ObjectName>.
- findReferencingRelations returns Map<String,ArrayList<String>>.
- getAllRelationIds returns List<String>.
- getAllRelationTypeNames returns List<String>.
- getRoleInfos returns List<RoleInfo>.
- getReferencedMBeans returns Map<ObjectName,ArrayList<String>>.
- sendRelationRemovalNotification takes List<ObjectName>.
- updateRoleMap takes List<ObjectName>.
- sendRoleUpdateNotification takes List<ObjectName>.
- sendRoleUpdateNotification takes List<ArrayList>.

RelationType.getRoleInfos returns List<RoleInfo>.
MBeanServerNotificationFilter.get{Enabled|Disabled}ObjectNames returns Vector<ObjectName>.

RelationNotification:
- constructor arg theUnregMBeanList should be List<ObjectName>.
- constructor args the{New|Old}RoleValue should be List<ObjectName>.
- getMBeansToUnregister returns List<ObjectName>.
- get{Old|New}RoleValue returns List<ObjectName>.

RelationService methods specified by RelationServiceMBean need same changes as it.
RelationSupport methods specified by Relation need same changes as it.
RelationTypeSupport.getRoleInfos returns List<RoleInfo>.
Role constructor and getRoleValue use List<ObjectName>.
RoleList extends List<Role>.
RoleUnresolved uses List<ObjectName>.
RoleUnresolvedList extends ArrayList<RoleUnresolved>.
Timer[MBean].get[All]NotificationIDs returns Vector<Integer>.