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PODoes simulation of closures in Java make sense?
 

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  1. PODoes simulation of closures in Java make sense?
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    <p>Languages that have closures, such as Ruby, enable elegant constructs to transform lists. Suppose we have a class</p> <pre><code>class QueryTerm { String value; public String getValue() {...} } </code></pre> <p>and a list of terms <code>List&lt;QueryTerm&gt; terms</code>, that we want to transform into its list of values <code>List&lt;String&gt; values</code>.</p> <p>In Ruby we could write something like:</p> <pre><code>values1 = terms.collect do |term| term.getValue() end </code></pre> <p>Java forces us to <strong>construct the result list</strong> and <strong>iterate through the terms collection</strong> ourselves (at least there is no iterator or index position involved since foreach was introduced):</p> <pre><code>Collection&lt;String&gt; values2 = new HashSet&lt;String&gt;(); for (QueryTerm term : terms) { values2.add(term.getValue()); } </code></pre> <p><a href="http://commons.apache.org/collections/" rel="nofollow noreferrer">Apache Commons</a> and <a href="http://google-collections.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Collections2.html" rel="nofollow noreferrer">Google Collections2</a> try to emulate closures in Java by using anonymous classes:</p> <pre><code>Collection&lt;String&gt; values3 = Collections2.transform(terms, new Function&lt;QueryTerm, String&gt;() { @Override public String apply(QueryTerm term) { return term.getValue(); } }); </code></pre> <p>The weird thing is, that this version has more lines of code and more characters than the original version! I would assume it is harder to understand for this reason. Therefore I dismissed the idea back when I saw it in Apache Commons. However, having seen it introduced in Google Collections recently I am starting to wonder if I am missing something.</p> <p><strong>Therefore my question: What is your opinion of the constructs above? Do you consider the <code>Collections2.transform()</code> version more readable/understandable than the default one? Am I missing something completely?</strong></p> <p>Best regards, Johannes</p>
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    1. USJim Ferrans
    1. USJoe23
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    1. COAnother alternative: http://code.google.com/p/lambdaj/
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    2. COYour example is so simple that it doesn't actually close over any variables...
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      1. USTom Hawtin - tackline
 

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