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copied!<p>The main difference between the two is when the concrete algorithm is chosen.</p> <p>With the <strong>Template method pattern</strong> this happens at <em>compile-time</em> by <em>subclassing</em> the template. Each subclass provides a different concrete algorithm by implementing the template's abstract methods. When a client invokes methods of the template's external interface the template calls its abstract methods (its internal interface) as required to invoke the algorithm.</p> <pre><code>class ConcreteAlgorithm : AbstractTemplate { void DoAlgorithm(int datum) {...} } class AbstractTemplate { void run(int datum) { DoAlgorithm(datum); } virtual void DoAlgorithm() = 0; // abstract } </code></pre> <p>In contrast, the <strong>Strategy pattern</strong> allows an algorithm to be chosen at <em>runtime</em> by <em>containment</em>. The concrete algorithms are implemented by separate classes or functions which are passed to the strategy as a parameter to its constructor or to a setter method. Which algorithm is chosen for this parameter can vary dynamically based on the program's state or inputs.</p> <pre><code>class ConcreteAlgorithm : IAlgorithm { void DoAlgorithm(int datum) {...} } class Strategy { Strategy(IAlgorithm algo) {...} void run(int datum) { this->algo.DoAlgorithm(datum); } } </code></pre> <h2>In summary:</h2> <ul> <li>Template method pattern: <strong>compile-time</strong> algorithm selection by <strong>subclassing</strong></li> <li>Strategy pattern: <strong>run-time algorithm</strong> selection by <strong>containment</strong></li> </ul>

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