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POUsing instanceof with Java Enums
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copied!<p>I have a situation where I'm receiving an <code>enum</code> from an external system, and for which I need to return an <code>enum</code> of our own. The two enums have the exact same literal values in them:</p> <pre><code>// externalEnum is guaranteed not to be null public static MyEnum enumToEnum(final Enum<? extends Enum<?>> externalEnum) { if( externalEnum instanceof MyEnum ) { return (MyEnum)enumType; } else { return MyEnum.valueOf(externalEnum.name()); } } </code></pre> <p>However, the compiler squeals the following:</p> <pre> [javac] found : java.lang.Enum<capture#117 of ? extends java.lang.Enum<?>> [javac] required: myEnum [javac] if( externalEnum instanceof MyEnum ) </pre> <p>I got a version of that function that works by simply returning <code>MyEnum.valueOf(externalEnum.name())</code> - it works and that's all that matters. However, I'm baffled about the compiler error. </p> <p>I'm trying to understand the reification process of generics in this case. An instance of <code>Enum<? extends Enum<?>></code> or simply <code>Enum<?></code> can be a <code>MyEnum</code> (given that the later can never be anything other than a subtype of the former.) </p> <p>So the <code>instanceof</code> test should work, but there seems to be something in the generic definition of <code>Enum</code> (and perhaps the fact that Enums cannot be extended) that causes the compiler to puke with that particular statement.</p> <p>The workaround for me is easy, but I like to understand the problems well, and any insight on this will be appreciated.</p> <ul> <li>Luis.</li> </ul>

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