TreeMap

treemap

A Red-Black tree based NavigableMap implementation. The map is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used.

当时我想用一个集合,该集合里装的对象按照这些对象的某属性排序

于是我用了额treemap ，把那个要排序的属性放到key里,并且用ReverseComparator制定了如何排序

Map<Date, Object> map = new TreeMap<Date,Object>(new ReverseComparator());Query query = getSession().createSQLQuery("select * from reply r where r.send_reply_person_id=? and r.sendcollect=? and r.sendrubbish=? or r.get_reply_person_id=? and r.getcollect=? and r.getrubbish=?").addEntity(Reply.class).setParameter(0, author.getId()).setParameter(1, true).setParameter(2, false).setParameter(3, author.getId()).setParameter(4, true).setParameter(5, false);List<Reply> replies = query.list();      Query query2 = getSession().createSQLQuery("select * from messagebox m where m.sendperson_id=? and m.sendcollect=? and m.sendrubbish=? or m.getperson_id=? and m.getcollect=? and m.getrubbish=?").addEntity(MessageBox.class).setParameter(0, author.getId()).setParameter(1, true).setParameter(2, false).setParameter(3, author.getId()).setParameter(4, true).setParameter(5, false);     List<MessageBox>messageBoxs = query2.list();          for(Reply r:replies){     map.put(r.getSendReplyTime(), r);     }     for(MessageBox m:messageBoxs){     map.put(m.getSendTime(), m);     }     System.out.println(map);

 

public class ReverseComparator implements Comparator<Date> {@Overridepublic int compare(Date o1, Date o2) {return o2.hashCode()-o1.hashCode();}}

所得的map则按照对象的sendreplytime和sendtime的倒序时间排序了(最新的放最前面)