code: public void add(final Object obj) {
  		final Class<?> clazz = obj.getClass();
  
  		if (this.clazzes.contains(clazz)) {
  			throw new IllegalArgumentException(
  					"Only one class-instance per benchmark allowed");
  		} else {
  			this.clazzes.add(clazz);
  			this.objects.add(obj);
  		}
  	}
docs: Adding a already instantiated objects to benchmark. Per benchmark, only
  one objects of each class is allowed.
  
  @param obj
  to be added