Talk:Chain-of-responsibility pattern

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Problem statement needed

Design patterns are general reusable solutions to a commonly occurring problem in software design. This article doesn't describe the problem the pattern aplies to. --89.155.228.227 (talk) 16:11, 1 March 2009 (UTC)[reply]

Pattern Application

Would appreciate an example in which applying this pattern resolves a design flaw... Thanks -- User:Euyyn

Is the example correct?

I think the output is not correct. "Writing to stdout:" should be "Writing to debug output:", or vice versa. But in this state I think the output does not match the Java source. - Regards Carsten —Preceding unsigned comment added by 80.144.237.11 (talk) 12:48, 31 July 2008 (UTC)[reply]

By my reading of how this pattern works, each successor is called until a successor in the chain handles the call. Then the chain stops. This is stated at the top of page 224 of the Design Patterns book. The example for Java shows each item on the chain being able to perform some example. So I don't think it is an actual example of a 'pure' chain of responsibility. Pcraven 20:10, 11 February 2007 (UTC)[reply]

I agree with Pcraven. Java example contradicts this statement "Each processing object contains a set of logic that describes the types of command objects that it can handle, and how to pass off those that it cannot to the next processing object in the chain." The example passes on the responsibility to next logger even if it could handle it. Sameergn (talk) 03:42, 8 March 2009 (UTC)[reply]

I agree and disagree with Pcraven. The Filter chain in the Servlet API is an implementation of this pattern. In the Filter chain the processing is continued just like the example, but in contradiction to the definition provided by the GoF. IMHO I think the people of SUN have thought thoroughly about the choice for this pattern. It turns out that the pattern can be used in a different setting then thought of by the GoF. Because I knew the FilterChain before reading the description by the GoF I was actually surprised to find out that the chain would stop. But thinking of selection of jdbc drivers made me understand. I think this example is correct although quite rudimentary and another example could be added to show the original way how the CoR can do its job. Loek Bergman (talk) 09:17, 16 June 2009 (UTC)[reply]

I disagree: Continuing the execution is a smart thing in some cases of course, but then that is clearly not this pattern but a custom one. I would rather categorize it as some kind of observer hacked together with a linked list because each member gets the message independently of the ones before. MoZo1 (talk) —Preceding undated comment added 14:46, 4 October 2009 (UTC).[reply]

Multiple language examples

Please stop removing examples without any discussion. There's some useful info there. Please discuss why we shouldn't have all these examples, instead of wholesale removing them. Thank you. peterl 11:05, 5 March 2007 (UTC)[reply]

Class Diagram

I was really expecting a more theoric example with diagrams and such... I think it is really useful to anyone who want to understand the pattern and apply into their project...189.59.206.104 (talk) 17:21, 16 July 2008 (UTC)[reply]

Python Example

I think the Python example does not show the Chain-of-responsibility pattern. In the example every handler will be executed. This does not represent the intended chain behavior. —Preceding unsigned comment added by 194.8.210.119 (talk) 10:19, 23 June 2010 (UTC)[reply]