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    <p>You're right, not sure what I was thinking there! Your comment inspired me to think about it further and I tested it and the cause of the problem has something to do with the recursive definition of the type variables <code>Job&lt;J extends Job&lt;J...</code>, but I'm not entirely clear why. One solution, remove the 'use' of J and R from your definitions.</p> <p>Longer answer:</p> <pre><code>import java.util.ArrayList; class Job&lt;J extends Job, R extends Run&gt; {} class Run&lt;J extends Job, R extends Run&gt; {} class Job2 extends Job&lt;Job2,Run2&gt; {} class Run2 extends Run&lt;Job2,Run2&gt; {} class RunList&lt;J extends Job, R extends Run&gt; extends ArrayList&lt;R&gt; {} class Foo { // #1 works now public void test1(RunList&lt;Job,Run&gt; why) {} // #2 works now too public void test2(RunList&lt;Job&lt;Job,Run&gt;,Run&lt;Job,Run&gt;&gt; why) {} // #3 still works public void test3(RunList&lt;Job2,Run2&gt; why) {} // #4 generic method public &lt;J extends Job, R extends Run&gt; void test4(RunList&lt;J,R&gt; why) {} public static void main(String[] args) { // Calling them even works... new Foo().test1(new RunList&lt;Job,Run&gt;()); new Foo().test2(new RunList&lt;Job&lt;Job,Run&gt;,Run&lt;Job,Run&gt;&gt;()); // Calling the generic method works too new Foo().test4(new RunList&lt;Job,Run&gt;()); new Foo().test4(new RunList&lt;Job&lt;Job,Run&gt;,Run&lt;Job,Run&gt;&gt;()); new Foo().test4(new RunList&lt;Job2,Run2&gt;()); // ...sort of // This doesn't work //new Foo().test1(new RunList&lt;Job&lt;Job,Run&gt;,Run&lt;Job,Run&gt;&gt;()); // This doesn't work //new Foo().test1(new RunList&lt;Job2,Run2&gt;()); } } </code></pre>
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    1. POTaming the type checker in Java Generics
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    1. USjaxzin
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    1. COWith regard to your statement of "The type boundary of 'extends' doesn't include the class/interface on the right-hand side; it only includes its subclasses/subinterfaces", I'm sorry, but I don't think so. List<Number> is assignable to List<T> where T extends Number.
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      1. USKohsuke Kawaguchi
    2. COKohsuke, how do you plan on using the generics? Is your goal to enforce at compile time that you're RunList only contains subclasses of Run that are known to be compatible with a certain Job subclass? For instance, RunList<Job2,Run2> is valid but RunList<Job2,MyCustomRun> isn't because Job2 was only written to work with Run2? Also, is there anything wrong with making Job and Run interfaces?
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