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    <p>There are some very useful 'higher order functions' which can do operations on lists using closures. Higher order functions are functions having 'function objects' as parameters.</p> <p>E.g. it is a very common operation to apply some transformation to every element in a list. This higher order function is commonly called 'map' or 'collect'. (See the *. spread operator of <a href="http://groovy.codehaus.org/Operators" rel="noreferrer" title="Groovy Operators">Groovy</a>).</p> <p>For example to square each element in a list without closures you would probably write:</p> <pre><code>List&lt;Integer&gt; squareInts(List&lt;Integer&gt; is){ List&lt;Integer&gt; result = new ArrayList&lt;Integer&gt;(is.size()); for (Integer i:is) result.add(i*i); return result; } </code></pre> <p>Using closures and map and the proposed syntax, you could write it like that:</p> <pre><code>is.map({Integer i =&gt; i*i}) </code></pre> <p>(There is a possible performance problem here regarding boxing of primitive types.)</p> <p>As explained by Pop Catalin there is another higher order function called 'select' or 'filter': It can be used to get all the elements in a list complying to some condition. For example:</p> <p>Instead of:</p> <pre><code>void onlyStringsWithMoreThan4Chars(List&lt;String&gt; strings){ List&lt;String&gt; result = new ArrayList&lt;String&gt;(str.size()); // should be enough for (String str:strings) if (str.length() &gt; 4) result.add(str); return result; } </code></pre> <p>Instead you could write something like</p> <pre><code>strings.select({String str =&gt; str.length() &gt; 4}); </code></pre> <p>using the proposal.</p> <p>You might look at the Groovy syntax, which is an extension of the Java language to support closures right now. See the chapter on collections of the <a href="http://groovy.codehaus.org/Collections" rel="noreferrer" title="Groovy User Guide">Groovy User Guide</a> for more examples what to do with closures.</p> <p>A remark:</p> <p>There is perhaps some clarification needed regarding the term 'closure'. What I've shown above are strictly spoken no closures. They are just 'function objects'. A closure is everything which can capture - or 'close over' - the (lexical) context of the code surrounding it. In that sense there are closures in Java right now, i.e. anonymous classes:</p> <pre><code>Runnable createStringPrintingRunnable(final String str){ return new Runnable(){ public void run(){ System.out.println(str); // this accesses a variable from an outer scope } }; } </code></pre>
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    1. PODoes Java need closures?
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    1. COUpvoted for knowing (and explaining) the distinction between closures and functions as values
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      1. USLogan Capaldo
 

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