[id] [int] IDENTITY (1, 1) NOT NULL ,PRIMARY KEY,UNIQUE

what must versus id of manipulation me!thank you

Use hibernate save:
namely error:

LogicDAO dao = new LogicDAO();
Logic logic=new Logic();
try {
Session s=dao.getSession();
Transaction t=s.beginTransaction();
logic.setUsername("aa");
logic.setPwd("aa");
dao.save(logic);
t.commit();

} catch (HibernateException e) {
System.err.println("Entity retrieval failed.");
e.printStackTrace();
} finally {
try {
dao.getSession().close();
} catch (Exception e) {
e.printStackTrace();
}
}

Error is:

Entity retrieval failed.
org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.hibernate.db.Logic
at org.hibernate.id.Assigned.generate(Assigned.java:33)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:91)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:186)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:175)
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:530)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:518)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:514)
at com.hibernate.db.LogicDAO.save(LogicDAO.java:27)
at com.hibernate.db.A.main(A.java:22)

This is a very common mistake : you seem to have specified something like <generator class="assigned"> inside the id tag of Logic.hbm.xml (or nothing 'cause I think this is the default), so your code is missing the setId() part.

If you want Hibernate to take care of this primary key (generating one when none is present : for new objects), use <generator class="native"> and create a sequence named hibernate_sequence in the db if it supports sequence. If not, hibernate should automatically use the right thing (identity, etc.) if you specified the right dialect in you hibernate.cfg.xml file.