code: @Override
  	public long getCount(long fromWhen, long toWhen,  boolean fromInclusive, boolean toInclusive){
  		NavigableMap<Long, AtomicLong> range = ((NavigableMap<Long, AtomicLong>)counters.getMap()).subMap(fromWhen, fromInclusive, toWhen, toInclusive);
  		long count = 0;
  		for(AtomicLong c: range.values()){
  			count += c.longValue();
  		}
  		return count;
  	}
docs: 获得在指定时间范围内的总频次.
  Please not that this method is not usable if the counter was created with a zero purgePeriod.
  @param fromWhen		开始时间
  @param toWhen		结束时间
  @param fromInclusive	是否包含开始时间
  @param toInclusive	是否包含结束时间
  @return				统计数