docs: public WeightRandom<T> add(WeightObj<T> weightObj) {
  		if(null != weightObj) {
  			final double weight = weightObj.getWeight();
  			if(weightObj.getWeight() > 0) {
  				double lastWeight = (this.weightMap.size() == 0) ? 0 : this.weightMap.lastKey();
  				this.weightMap.put(weight + lastWeight, weightObj.getObj());// 权重累加
  			}
  		}
  		return this;
  	}