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POClearest way to comma-delimit a list?
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  1. POClearest way to comma-delimit a list?
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    copied!<p>What is the clearest way to comma-delimit a list in Java?</p> <p>I know several ways of doing it, but I'm wondering what the best way is (where "best" means clearest and/or shortest, not the most efficient.</p> <p>I have a list and I want to loop over it, printing each value. I want to print a comma between each item, but not after the last one (nor before the first one).</p> <pre><code>List --&gt; Item ( , Item ) * List --&gt; ( Item , ) * Item </code></pre> <p>Sample solution 1:</p> <pre><code>boolean isFirst = true; for (Item i : list) { if (isFirst) { System.out.print(i); // no comma isFirst = false; } else { System.out.print(", "+i); // comma } } </code></pre> <p>Sample solution 2 - create a sublist:</p> <pre><code>if (list.size()&gt;0) { System.out.print(list.get(0)); // no comma List theRest = list.subList(1, list.size()); for (Item i : theRest) { System.out.print(", "+i); // comma } } </code></pre> <p>Sample solution 3:</p> <pre><code> Iterator&lt;Item&gt; i = list.iterator(); if (i.hasNext()) { System.out.print(i.next()); while (i.hasNext()) System.out.print(", "+i.next()); } </code></pre> <p>These treat the first item specially; one could instead treat the last one specially.</p> <p>Incidentally, here is how <code>List</code> <code>toString</code> <em>is</em> implemented (it's inherited from <code>AbstractCollection</code>), in Java 1.6:</p> <pre><code>public String toString() { Iterator&lt;E&gt; i = iterator(); if (! i.hasNext()) return "[]"; StringBuilder sb = new StringBuilder(); sb.append('['); for (;;) { E e = i.next(); sb.append(e == this ? "(this Collection)" : e); if (! i.hasNext()) return sb.append(']').toString(); sb.append(", "); } } </code></pre> <p>It exits the loop early to avoid the comma after the last item. BTW: this is the first time I recall seeing "(this Collection)"; here's code to provoke it:</p> <pre><code>List l = new LinkedList(); l.add(l); System.out.println(l); </code></pre> <p>I welcome any solution, even if they use unexpected libraries (regexp?); and also solutions in languages other than Java (e.g. I think Python/Ruby have an <em>intersperse</em> function - how is <em>that</em> implemented?).</p> <p><em>Clarification</em>: by libraries, I mean the standard Java libraries. For other libraries, I consider them with other languages, and interested to know how they're implemented.</p> <p><em>EDIT</em> toolkit mentioned a similar question: <a href="https://stackoverflow.com/questions/285523/last-iteration-of-for-loop-in-java">Last iteration of enhanced for loop in java</a></p> <p>And another: <a href="https://stackoverflow.com/questions/156650/does-the-last-element-in-a-loop-deserve-a-separate-treatment">Does the last element in a loop deserve a separate treatment?</a></p>
 

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