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POCan Class<V> take multiple bounds on the generic type?
 

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    <p>The following code compiles: </p> <pre><code>import java.util.ArrayList; public class ClassTest { private ArrayList&lt;Class&lt;? extends Interface1&gt;&gt; testClass = new ArrayList&lt;Class&lt;? extends Interface1&gt;&gt;(); private interface Interface1 {} } </code></pre> <p>But the following code produces six errors: </p> <pre><code>import java.util.ArrayList; public class ClassTest { private ArrayList&lt;Class&lt;? extends Interface1 &amp; Interface2&gt;&gt; testClass = new ArrayList&lt;Class&lt;? extends Interface1 &amp; Interface2&gt;&gt;(); private interface Interface1 {} private interface Interface2 {} } </code></pre> <p>Errors: </p> <pre><code>ClassTest.java:5: &gt; expected private ArrayList&lt;Class&lt;? extends Interface1 &amp; Interface2&gt;&gt; testClass = ^ ClassTest.java:5: ';' expected private ArrayList&lt;Class&lt;? extends Interface1 &amp; Interface2&gt;&gt; testClass = ^ ClassTest.java:5: &lt;identifier&gt; expected private ArrayList&lt;Class&lt;? extends Interface1 &amp; Interface2&gt;&gt; testClass = ^ ClassTest.java:6: &gt; expected new ArrayList&lt;Class&lt;? extends Interface1 &amp; Interface2&gt;&gt;(); ^ ClassTest.java:6: '(' or '[' expected new ArrayList&lt;Class&lt;? extends Interface1 &amp; Interface2&gt;&gt;(); ^ ClassTest.java:6: illegal start of expression new ArrayList&lt;Class&lt;? extends Interface1 &amp; Interface2&gt;&gt;(); ^ </code></pre> <p>It's pretty clear that the compiler isn't recognizing the <code>&amp;</code> being used for multiple generic bounds on <code>Class</code>. Are you not allowed multiple bounds on the type parameter for <code>Class</code>? What am I supposed to do if I want an <code>ArrayList</code> of <code>Class</code>es that implement both <code>Interface1</code> and <code>Interface2</code>?</p> <p><strong>Motivation:</strong> The code I'm working on at the moment has a lot of declarations like this: </p> <pre><code>private static HashMap&lt;String, Class&lt;? extends ApproximativeMode&gt;&gt; approximativeMethod = new HashMap&lt;String, Class&lt;? extends ApproximativeMode&gt;&gt;(); </code></pre> <p>They map a string to a class which contains a 'method' for doing a certain calculation. Each separate hashmap uses a different wildcard for the classes (so <code>ApproximativeMode</code> might be replaced with <code>ExactMode</code> for the hashmap containing all of the exact methods). </p> <p>I've just gone through all of the methods, making them implement a new interface, <code>NamedMethod</code>, which has a method that gets their full, displayed name (e.g. "Linear hydroxyadenine method"). I now want to put all of the hashmaps into an <code>ArrayList</code> so that I can write an iterator that goes over the hashmaps and displays their full names. So I might end up with: </p> <p><strong>Approximative Methods</strong></p> <p>von Ahsen et al.</p> <p>Owen et al.</p> <p>etc.</p> <p><strong>Exact Methods</strong></p> <p>Santalucia et al. </p> <p>LHM</p> <p>etc.</p> <p>etc.</p> <p>So my declaration of the <code>ArrayList</code> holding all the hashmaps is: </p> <pre><code>private ArrayList&lt;Hashmap&lt;String, Class&lt;? extends NamedMethod&gt;&gt;&gt; namedMethods; </code></pre> <p>Of course, none of the hashmaps are actually of that type, but I was hoping that I could add <code>NamedMethod</code> to the wildcard in each one and get an <code>ArrayList</code> of them all. Clearly that isn't possible. </p> <p>If this isn't clear, let me know and I'll fix it up. </p>
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