java set 转 list 并排序

        Set<Role> userRolesSet = userManage.findUserByID(userID).getRoles();
        List<Role> userRoles = new ArrayList<Role>(userRolesSet);
	Collections.sort(userRoles, new Comparator<Role>() {
		public int compare(Role arg0, Role arg1) {
			return -arg0.getCreateDate().compareTo(arg1.getCreateDate());
		}
	});

compare中的负号的作用是倒序，因为compareTo方法默认排序是正序（即从小到大）.

执行完毕的userRoles按role的createDate倒序排列