code: public T next() {
  		if(MapUtil.isEmpty(this.weightMap)) {
  			return null;
  		}
  		final double randomWeight = this.weightMap.lastKey() * random.nextDouble();
  		final SortedMap<Double, T> tailMap = this.weightMap.tailMap(randomWeight, false);
  		return this.weightMap.get(tailMap.firstKey());
  	}
docs: 下一个随机对象
  
  @return 随机对象