code: public static <K> HashMap<K, MutableLong> createMutableLongValueMap(int initialCapacity, float loadFactor) {
  		return new HashMap<K, MutableLong>(initialCapacity, loadFactor);
  	}
docs: 创建值为可更改的Long的HashMap. 可更改的Long在更改时不需要重新创建Long对象，节约了内存
  
  @param initialCapacity 建议为16
  @param loadFactor 建议为0.5