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The second pattern I want to discuss is the
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strategy pattern, which provides a way to configure a
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class with one of many behaviors. What does that
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mean? Well, more precisely, this pattern allows for defining
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a family of algorithms, encapsulating them into separate classes,
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so each algorithm in one class, and making these
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classes interchangeable, but providing a common interface for all
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the encapsulated algorithms. So in essence, the intent of
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a strategy pattern is to allow for switching between
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different algorithms for accomplishing a given task. For example, imagine
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having different sorting algorithms with different space or time
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tradeoffs. You might want to be able to have them
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all available and use different ones in different situations.
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And this pattern is applicable not only when we have
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different variants of an algorithm, but also when we
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have many related classes that differ only in their behavior.
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So let's get more concrete and see how this is
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done. And I'm going to do it as before, by
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discussing the structure and the participants for this strategy pattern.
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In this case, we have 3 types of participants for this
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pattern, the context, the algorithm, and the concrete strategies. There
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can be as many as the number of behaviors that
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I need to implement. So, let's see what those are.
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The context is the interface to the outside world. It maintains
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a reference to the current algorithm and allows for
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updating this reference at run time. So, basically the outside
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world will invoke the functionality provided by the different algorithms,
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by using this interface. And depending on which algorithm is
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currently selected, that's the one that will be executed when
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the functionality is involved. The algorithm, also called the strategy,
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so that's where the pattern gets its name, Is the
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common interface for the different algorithims. So all the algorithms
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implement this interface. Finally, the concrete strategies are the
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actual implementations of the algorithms. So if I have 10
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different variants of my algorithm, I will implement 10 different
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concrete strategies. They will all be implementations of this interface.
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