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copied!<p>As I explain in <a href="https://stackoverflow.com/questions/2248390/java-generics-collections-max-signature-and-comparator/2248503#2248503">my answer</a> to another question, PECS is a mnemonic device created by Josh Bloch to help remember <strong>P</strong>roducer <code><strong>e</strong>xtends</code>, <strong>C</strong>onsumer <code><strong>s</strong>uper</code>.</p> <blockquote> <p>This means that when a parameterized type being passed to a method will <em>produce</em> instances of <code>T</code> (they will be retrieved from it in some way), <code>? extends T</code> should be used, since any instance of a subclass of <code>T</code> is also a <code>T</code>.</p> <p>When a parameterized type being passed to a method will <em>consume</em> instances of <code>T</code> (they will be passed to it to do something), <code>? super T</code> should be used because an instance of <code>T</code> can legally be passed to any method that accepts some supertype of <code>T</code>. A <code>Comparator<Number></code> could be used on a <code>Collection<Integer></code>, for example. <code>? extends T</code> would not work, because a <code>Comparator<Integer></code> could not operate on a <code>Collection<Number></code>.</p> </blockquote> <p>Note that generally you should only be using <code>? extends T</code> and <code>? super T</code> for the parameters of some method. Methods should just use <code>T</code> as the type parameter on a generic return type.</p>

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