java extend or wrap a class to add extra functionality

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

It sounds like you're asking whether you should favor inheritance or composition in your situation. I would say that you are not creating a new implementation of List and you don't really care how List is implemented, so inheritance doesn't fit your problem. Instead, you're providing paging functionality. I would create a class that generically wraps up (encapsulates) the paging logic using List or some other generic collection.