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This is really off-topic for these forums. You might do better on StackOverflow.com. I'll just say that although the first Design Patterns book came as a revelation to me, it was more for (a) the nomenclature (decorator, factory, facade, etc) which is still with us and (b) about five of the original patterns, which told me things I didn't already know. I've never used any of the others, including Command, and the whole design patterns thing quickly degenerated into farce with what seemed like a sustained attempt to reduce the whole of computer science to design patterns, which really isn't the point. As an example, there is one in another book called Type Object, which is nothing but 3rd normal form, which can be defined roughly in a couple of sentences. This pattern went on for dozens of pages with a very artificial example. I wrote to the mailing list about it: 'Type Object considered hilarious'. I got a rude reply from the original author, which I guess I expected, but also an incredible response from the list owner, saying I should recast my objections in the form of a design pattern. That lost it for me. True story. Moral: don't take this religion, or any IT religion, too seriously. They come around every 18 months or so with the regularity of the next bit of Moore's Law. I've seen dozens of them come and go since 1971, all with something to say, all 90% nonsense.
See here for a longer version of this incident.
Thank you so much EJP. Before (long back when sun forums exist) we used to have a forum for design patterns and modeling issues. May be i am vague. I remember that i had a very long discussion about UML issue on the form. So i have looked for that forum and unable to find it, so posted in general forum. Sorry for this and a huge thank you for answering without getting irritated.
I have done some ground work to understand this. I have documented my understanding of this design pattern. The following is the link http://yaragalla.blogspot.in/2013/10/command-design-pattern.html
I have posted the link thinking that it might help somebody who is having the problem of understanding this design pattern. Nothing much. Thank u so much.
Thank U so much.