Why is returning List<? extends T> read-only and returning List<? super T> write-only?
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  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://stackoverflow.com/questions/1368166/what-is-a-difference-between-super-e-and-extends-e">What is a difference between &lt;? super E&gt; and &lt;? extends E&gt;?</a>  </p>
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<p>Some Java programmers on a team I'm on are writing functions that return objects of type <code>List&lt;? extends T&gt;</code> to make read-only lists and return objects of type <code>List&lt;? super T&gt;</code> to make write-only lists.</p>

<p>In Java, what makes <code>List&lt;? extends T&gt;</code> read-only and <code>List&lt;? super T&gt;</code> write-only?</p>
