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<p>The <a href="http://en.wikipedia.org/wiki/Template_method_pattern">Template Method Pattern</a> abstracts away the details of several algorithms. The generic part of an algorithm is contained within a base class. Particular implementation details are captured within base classes. The generic pattern of classes involved looks like this:</p>

<p><img class="confluence-embedded-image" src="/download/attachments/231080116/TemplateMethodClasses.gif?version=1&amp;modificationDate=1369341812073" data-image-src="/download/attachments/231080116/TemplateMethodClasses.gif?version=1&amp;modificationDate=1369341812073" data-linked-resource-id="231375565" data-linked-resource-type="attachment" data-linked-resource-default-alias="TemplateMethodClasses.gif" data-base-url="http://docs.codehaus.org" data-linked-resource-container-id="231080116" title="null > TemplateMethodClasses.gif"></p>

<h3>Example</h3>

<p>In this example, <code>Accumulator</code> captures the essence of the accumulation algorithm. The base classes <code>Sum</code> and <code>Product</code> provide particular customised ways to use the generic accumulation algorithm.</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
abstract class Accumulator {
    protected initial
    abstract doAccumulate(total, v)
    def accumulate(values) {
        def total = initial
        values.each { v -> total = doAccumulate(total, v) }
        total
    }
}

class Sum extends Accumulator {
    def Sum() { initial = 0 }
    def doAccumulate(total, v) { total + v }
}

class Product extends Accumulator {
    def Product() { initial = 1 }
    def doAccumulate(total, v) { total * v }
}

println new Sum().accumulate([1,2,3,4])
println new Product().accumulate([1,2,3,4])
</pre></td></tr></table>

<p>The resulting output is:</p>

<p>In this particular case, you could use Groovy's inject method to achieve a similar result using Closures:</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
Closure addAll = { total, item -> total += item }
def accumulated = [1, 2, 3, 4].inject(0, addAll)
println accumulated    // => 10
</pre></td></tr></table>

<p>Thanks to duck-typing, this would also work with other objects which support an add (<code>plus()</code> in Groovy) method, e.g.:</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
accumulated = [ "1", "2", "3", "4" ].inject("", addAll)
println accumulated    // => "1234"
</pre></td></tr></table>

<p>We could also do the multiplication case as follows:</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
Closure multAll = { total, item -> total *= item }
accumulated = [1, 2, 3, 4].inject(1, multAll)
println accumulated    // => 24
</pre></td></tr></table>

<p>Using closures this way looks more like the <a class="confluence-link" href="/display/GROOVY/Strategy+Pattern" data-linked-resource-id="78100" data-linked-resource-type="page" data-linked-resource-default-alias="Strategy Pattern" data-base-url="http://docs.codehaus.org">Strategy Pattern</a> but if we realise that the built-in <code>inject</code> method is the generic part of the algorithm for our template method, then the Closures become the customised parts of the template method pattern.</p>