List 乱序

HashSet<Integer> set = new HashSet<Integer>();
		int maxSize = typequestionlist.size();
		sortlist = new HashSet();
		while (true) {
			int randNumber = (int) (Math.random() * maxSize + 1) - 1;
			set.add(randNumber);
			if (set.size() > 5) {
				break;
			}
			for (int a : set) {
				Question question = typequestionlist.get(a);
				sortlist.add(question);
			}
		}
		rlist = new ArrayList(sortlist);

再来个 SQL：select * from Question where question_type='Java' and rownum<=10 order by dbms_random.value