In the first case, the object itself contains its own operation. (Obviously, other parameters can be for multiple items -. A detail) Every object is in memory, the operations separately. Therefore, eat more memory and thread-safe. In addition, a variety of objects in case you do not have any template. Two of the case, if any of the other course may be used to identify an object or registered in other ways for example. identification time. (The latter is of course not always praktkus.) In the second case, the operation of a static method. In one piece, but if an item has to be given as a parameter and not thread-safe. And it's not talked about, if we want to make the object of a derived class already is.