用hashmap可以保存，为什treemap就不行了

Question

错误：
javax.servlet.ServletException: com.CallCenter.bo.TbBulletin
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:523)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:421)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:627)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
com.CallCenter.common.FilterEncoding.doFilter(FilterEncoding.java:39)
root cause java.lang.ClassCastException: com.CallCenter.bo.TbBulletin
java.util.TreeMap.compare(TreeMap.java:1093)
java.util.TreeMap.put(TreeMap.java:465)
com.CallCenter.web.struts.action.QueryBulletion.execute(QueryBulletion.java:38)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:419)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:627)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
com.CallCenter.common.FilterEncoding.doFilter(FilterEncoding.java:39)代码：
HashMap<TbBulletin, String> map = new HashMap<TbBulletin, String>();
List bulletionList = bulletionService.getAll();
if(bulletionList!=null && bulletionList.size()>0){
Object obj[] = null;
for(int i = 0;i<bulletionList.size();i++){
obj= (Object[])bulletionList.get(i);
map.put((TbBulletin)obj[0], String.valueOf(obj[1]));
}
}

Answer 1

java.lang.ClassCastException: com.CallCenter.bo.TbBulletin 最后一句((TbBulletin)obj[0]   你确认下是否这个对象能向下转型

Answer 2

很明显,类型转换异常
(TbBulletin)obj[0],obj[0]是什么类型,能转成TbBulletin?

Answer 3

那为什么用hashMap可以了？？而treeMap不行？？我只是用hasMap他不能排序,而treeMap可以排序.而3楼的说我转型错误？？因为我知道那个obj[0]是个tbBulletin的对象

Answer 4

排序时， 出现的错误， 例如：   TbBulletin 实现Comprable 接口了没 ；
  
  TbBulletin 具有可比性没； 等等