Question

When you want to add some extra information into a class, what way would you prefer: would you extend that class or make a wrapper around it?

In my particular scenario, I want to add some pagination information with a List that I get from database. That pagination information will include:

int currentPage;
int totalResults;
int containedResultsIndex;
int totalcontainedResults;

and a couple of methods:

Boolean isNextPageAvailable();
Boolean isPrevPageAvailable();

Whats your opinion, extend or wrap?

Answer 1

• in your case wrap the existing List and make your class implement List itself, delegating all methods the the original list (which is passed in constructor, for example)
• inheritance isn’t always wrong, but in this case you won’t know what class to extend – will it be ArrayList, or LinkedList ?