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Over the years, I’ve tried to avoid instanceof whenever possible. Using polymorphism or the visitor pattern where applicable. I suppose it simply eases maintenance in some situations… Are there any other drawbacks that one should be aware of?
I do however see it here and there in the Java libraries so I suppose it has its place? Under what circumstances is it preferable? Is it ever unavoidable?
I can imagine some cases, for example you have some objects of a library, which you can’t extend (or it would be inconvenient to do so), perhaps mixed with some objects of your, all with same base class, together in a collection.
I suppose that in such case, using instanceof to distinguish some processing on these objects might be useful.
Idem in some maintenance of legacy code where you cannot inject some new behavior in lot of old classes just to add a new little feature or some bug fix…