code: public String[] lookupString(int[] ids) {
  		String[] vals = new String[ids.length];
  		for(int i = 0; i < ids.length; i++)	{
  			vals[i] = index.get(ids[i]);
  		}
  		return vals;
  	}
docs: 查找一组编号对应的标记
  @param ids 索引编号数组
  @return 标记数组