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POWhy doesn't autoboxing work in this case with generics?
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  1. POWhy doesn't autoboxing work in this case with generics?
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    copied!<blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/517751/java-array-of-primitive-data-types-does-not-autobox">Java: Array of primitive data types does not autobox</a> </p> </blockquote> <p>I've been doing some Java lately (mostly as a recap on what I did at university as my current job doesn't involve any Java at all) and one thing that never got introduced to us properly is Generics.</p> <p>I've been doing the Generics tutorial on the Oracle Java website and I've been stumped by the following example that I modified a bit:</p> <pre><code>public static &lt;Integer extends Comparable&lt;Integer&gt;&gt; int countGreaterThan(Integer [] anArray, Integer elem) { int count = 0; for (Integer e : anArray) if (e.compareTo(elem) &gt; 0) ++count; return count; } </code></pre> <p>And I use this method to compare an Integer array with the following Integer:</p> <pre><code>Integer [] numarr = {1, 2, 3, 4 , 5}; Integer num = new Integer(5); int count = Util.countGreaterThan(arrnum, num); </code></pre> <p>This seems to work fine, however if I pass a primitive array and a primitive int, it doesn't:</p> <pre><code>int [] arrnum = {1, 2, 3, 4 , 5}; int othernum = 3; int count = Util.countGreaterThan(arrnum, othernum); </code></pre> <p>The compiler complains with:</p> <pre><code>method countGreaterThan in class Generics.Util cannot be applied to given types; required: Integer[],Integer found: int[],int reason: no instance(s) of type variable(s) Integer exist so that argument type int conforms to formal parameter type Integer </code></pre> <p>The tutorials seemed to be pretty adamant that Java will always autobox/unbox objects and primitives as necessary and yet it won't do it in this particular case, what am I missing?</p> <p>Also what could be a good way to generalise this comparing method as much as possible? If I used T instead of Integer, then it would look for a T object, rather than whatever I pass to it.</p> <p>I apologise if the post is confusing and if I seem pretty ignorant about the stuff I talk about above, it's just that I've been working primarily as a perl programmer (and not as particularly experienced one either) and generalising there seems as less of an issue (due to the lack of type enforcement).</p> <p>Thanks in advance!</p>
 

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