code: public void setMultiplicity(O object, int multiplicity) {
  		if (!contains(object) && multiplicity < 1) {
  			return;
  		}
  		if (contains(object) && multiplicity < 1) {
  			remove(object);
  			return;
  		}
  		if (multiplicities.containsKey(object)) {
  			int oldMultiplicity = multiplicities.get(object);
  			decMultiplicityCount(oldMultiplicity);
  		}
  		incMultiplicityCount(multiplicity);
  		multiplicities.put(object, multiplicity);
  	}
docs: Sets the multiplicity of the given object to the given number.<br>
  In case the multiplicity is 0 or negative, the given object is
  removed from the multiset.
  
  @param object The object whose multiplicity is set.
  @param multiplicity The multiplicity for the given object to set.