Difference between Strategy Pattern and Factory Pattern?

Is there any major difference between Strategy Pattern and Factory Pattern? As for me its look alike and I am a bit confused which to use when. I see that the Factory Pattern gets me the object of desired type which we can also achieve using Strategy Pattern...

Imran Khan, Aug 06, 2010

Reply 1

Yes, they seem to be same but they do have a visible difference. Factory's sole purpose is to create objects and strategy's sole intent to is to provide a mechanism to select different algorithm.

You can use "factory" to create objects of "strategy". For. e.g. take the following example from dofactory for strategy..

SortedList studentRecords = new SortedList();

studentRecords.Add("Samual");

studentRecords.Add("Jimmy");

studentRecords.SetSortStrategy(new QuickSort());

studentRecords.Sort();

studentRecords.SetSortStrategy(new ShellSort());

studentRecords.Sort();

Now note here, the type passed in the "SetSortStrategy" method is "hardcoded" and this will be a fragile design if this is some kind of production code.

To make this more resilent to change introduce factory (this is a crude example and is only for demonstration purpose)

SortStrategy algo = SortFactory.GetQuickSort(); // something like this... the actual instance creation of quicksort is controlled by the SortFactory and this is well abstracted from the client.

studentRecords.SetSortStrategy(algo);

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Let me know whether this is useful or you need more clarifications.

Regards,

Rajesh Pillai

Rajesh Pillai, Aug 06, 2010