Decorator pattern versus sub classing

Question

I can solve the problem of adding functionality by adding sub classing then why should I use decorator pattern what\'s the real advantage of decorator pattern ?

Answer 1

An example from GoF:

Suppose you have a TextView class. Then in someplace you want a scrolled text view, so you subclass TextView and create ScrolledTextView class. And in some other place, you want a border around text view. So you subclass again and create BorderedTextView. Well, now in someplace you want border and scroll both. None of the previous two subclasses have both capabilities. So you need to create a 3rd one. When creating a ScrolledBorderedTextView you are actually duplicating the effort. You don't need this class if you have any way to compose the capability of the previous two. Well, things can go worse and these may lead to an unnecessary class explosion.

Basically, by using the decorator pattern you can add any number of additional responsibility to object at RUNTIME which you can not achieve by subclassing without potentially damaging your code structure or adding many duplicate combinations for subclasses.

But one thing, Design patterns are not something that you must use.
Whether a pattern is needed or not is dependent on your particular problem, you want to maintain the code for a long time or not, whether you want to extend or not and on many other factors like these.
And there is no pattern that is useful in all cases.
A pattern (decorator or anything else) suitable for a situation may not be a good choice for another situation.