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    <p>You'll need to use a generic helper method with an unchecked cast:</p> <pre><code>private static &lt;T extends Enum&lt;T&gt; &amp; Marshallable&gt; void fooHelper(Class&lt;? extends Marshallable&gt; type) { if (type.isEnum()) { //This is safe because of the isEnum check, and we don't return any //type with T (important because the caller can specify what T is). @SuppressWarnings("unchecked") final Class&lt;T&gt; enumType = (Class&lt;T&gt;)type; final List&lt;T&gt; enumConstants = Arrays.asList(enumType.getEnumConstants()); foo(enumConstants); } } </code></pre> <p>The reason your version doesn't work is because with <code>T extends Enum&lt;T&gt; &amp; Marshallable</code>, <code>T</code> is recursively bound - something that can only be expressed with type parameters. The wildcard type arguments in <code>? extends Enum&lt;? extends Marshallable&gt;</code> no longer specify that relationship.</p> <p><strong>WARNING:</strong> It's imperative that <code>fooHelper</code> doesn't return a type containing <code>T</code> because this could cause heap pollution. For example:</p> <pre><code>private static &lt;T extends Enum&lt;T&gt; &amp; Marshallable&gt; List&lt;T&gt; unsafeFooHelper(Class&lt;? extends Marshallable&gt; type) { if (type.isEnum()) { //no longer safe! @SuppressWarnings("unchecked") final Class&lt;T&gt; enumType = (Class&lt;T&gt;)type; return Arrays.asList(enumType.getEnumConstants()); } return Collections.emptyList(); } enum Enum1 implements Marshallable { ONE, TWO } enum Enum2 implements Marshallable { A, B } ... //caller lies about what T is: List&lt;Enum2&gt; enumConstants = Main.&lt;Enum2&gt;unsafeFooHelper(Enum1.class); //sometime later... Enum2 enumConstant = enumConstants.get(0); //ClassCastException </code></pre>
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    1. COIt worked fine when running from Eclipse but now I noticed it gives compilation errors when I do maven build. The line I call helper gives the error: "type parameters of <T>void cannot be determined; no unique maximal instance exists for type variable T with upper bounds Marshallable"
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    2. CO@acheron55 It appears to work [here](http://ideone.com/H3YslT) (sun-jdk-1.7.0_10). Are you using Java 6 or earlier?
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    3. COYes I am using Java 6. I think it is similar to problem here: http://stackoverflow.com/questions/314572/bug-in-eclipse-compiler-or-in-javac As a workaround I had to lie about T, by passing a "hardcoded" enum & marshallable type to helper call which I didn't really like. MarshallingTest.<ConcreteEnum1>fooHelper(clazz);
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