com.one2many.Author objAuthorRs = null;
com.one2many.Author objAuthorERROR = null;
String strQueryString = "select p from com.one2many.Author as p where p.AUTHORID like :ID";
net.sf.hibernate.Query objQuery = objSession.createQuery(strQueryString);
objQuery.setString("ID","111");
//java.util.Iterator objIteratorRs = objQuery.iterate();
//while(objIteratorRs.hasNext())
//{
// objAuthorRs = (com.one2many.Author)objIteratorRs.next();
// System.out.println(objAuthorRs.getALIAS());
//}
for(java.util.Iterator objIteratorRs = objQuery.iterate();objIteratorRs.hasNext();)
{
objAuthorRs =(com.one2many.Author)objIteratorRs.next();
//objAuthorRs =(com.one2many.Author)objQuery.list().get(0);
System.out.println(objAuthorRs.getALIAS());
}

//strQueryString = "select a.AUTHORID,a.ALIAS from com.one2many.Author AS a WHERE a.AUTHORID LIKE :ID";
strQueryString = "select a.AUTHORID from com.one2many.Author as a where a.AUTHORID like :AUTHORID";
net.sf.hibernate.Query objQueryERROR= objSession.createQuery(strQueryString);
//objQuery = objSession.createQuery(strQueryString);
objQueryERROR.setString("AUTHORID","111");
for(java.util.Iterator objIteratorERROR = objQueryERROR.iterate();objIteratorERROR.hasNext();)
{
objAuthorERROR =(com.one2many.Author)objIteratorERROR.next();
//objAuthorRs =(com.one2many.Author)objQuery.list().get(0);
System.out.println(objAuthorERROR.getALIAS());
}

the first select runs ok,but the second can't runs...,i don't know why?
the second throw the error:
java.lang.ClassCastException

at com.one2many.hibernateselect.main(hibernateselect.java:106)

thanks a lot!

In your first query you are asking for an object, so the entire object gets returned. In your second query though you are asking for specific fields, which will be returned as n Object if one field or an Object[] array for more than one field. You then need to cast from that Object or Object[] to the correct type that you are expecting (such as String or Integer etc.)