code: public void ensureCapacity (int additionalCapacity) {
  		int newCapacity = size + additionalCapacity;
  		if (items.length < newCapacity) resize(newCapacity);
  	}
docs: Increases the size of the backing array (if necessary) to accommodate the specified number of additional items. Useful
  before adding many items to avoid multiple backing array resizes.
  @param additionalCapacity the number of additional items