Hibernate count rows with some criterias

Criteria crit = session.createCriteria(Person.class);
crit.add( Restrictions.isNotNull("birthDate"));
crit.add( Restrictions.eq("isStudent", true));
List<Person> students = crit.list();
Integer count = students.size();

or if just want a single count value, and no list returned :

Criteria crit = session.createCriteria(Person.class);
crit.setProjection(Projections.rowCount());
crit.add( Restrictions.isNotNull("birthDate"));
crit.add( Restrictions.eq("isStudent", true));
return (Long) crit.uniqueResult(); 

Criteria crit = session.createCriteria(Person.class);
crit.add( Restrictions.isNotNull("birthDate"));
crit.add( Restrictions.eq("isStudent", true));
crit.setProjection(Projections.rowCount());
Integer count = (Integer)crit.uniqueResult();

Number count = (Number) session.createQuery(
    "select count(p.id) from Person p"
    + " where p.birthDate is not null and p.isStudent = true").uniqueResult();