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    <p>What is erased is <code>E</code>. You can't, in fact, do <code>if (e instanceof E)</code>, because the type parameter <code>E</code> is erased. However, <code>String</code> is not a parameterized type, and <code>e</code> does have a run-time type, so <code>if (e instanceof String)</code> works just fine.</p> <h3><a href="http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.20.2" rel="nofollow noreferrer">JLS 15.20.2 Type comparison <code>instanceof</code> operator</a></h3> <blockquote> <pre><code>RelationalExpression: RelationalExpression instanceof ReferenceType </code></pre> <p>The type of a <code>RelationalExpression</code> operand of the <code>instanceof</code> operator must be a reference type or the <code>null</code> type; otherwise, a compile-time error occurs. The <code>ReferenceType</code> mentioned after the <code>instanceof</code> operator must denote a reference type; otherwise, a compile-time error occurs. <strong>It is a compile-time error if the</strong> <code>ReferenceType</code> <strong>mentioned after the</strong> <code>instanceof</code> <strong>operator does not denote a reifiable type</strong> (§4.7).</p> </blockquote> <p><code>String</code> is a reifiable type. <code>E</code> is not.</p> <h3><a href="http://java.sun.com/docs/books/jls/third_edition/html/typesValues.html#4.7" rel="nofollow noreferrer">JLS 4.7 Reifiable Types</a></h3> <blockquote> <p>Because some type information is erased during compilation, not all types are available at run time. Types that are completely available at run time are known as reifiable types. A type is reifiable if and only if one of the following holds:</p> <ul> <li>It refers to a non-generic type declaration.</li> <li>It is a parameterized type in which all type arguments are unbounded wildcards</li> <li>It is a raw type.</li> <li>It is a primitive type.</li> <li>It is an array type whose component type is reifiable.</li> </ul> </blockquote> <h3>See also</h3> <ul> <li><a href="https://stackoverflow.com/questions/1570073/java-instanceof-and-generics">Java: Instanceof and Generics</a></li> <li><a href="https://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it">What is a raw type and why shouldn’t we use it?</a> <ul> <li><code>instanceof</code> and <code>.class</code> literal are the two exceptions where raw type in new code can be used</li> </ul></li> </ul>
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