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POJava: Cyclic generic type relation doesn't allow cast from supertype (javac bug)
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  1. POJava: Cyclic generic type relation doesn't allow cast from supertype (javac bug)
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    copied!<p>I encounter a totally strange behavior of the Java compiler.<br> I can't cast a supertype to a subtype when <strong>cyclic generic type relation</strong> is involved.</p> <p><strong>JUnit test case</strong> to reproduce the problem:</p> <pre><code>public class _SupertypeGenericTest { interface ISpace&lt;S extends ISpace&lt;S, A&gt;, A extends IAtom&lt;S, A&gt;&gt; { } interface IAtom&lt;S extends ISpace&lt;S, A&gt;, A extends IAtom&lt;S, A&gt;&gt; { } static class Space implements ISpace&lt;Space, Atom&gt; { } static class Atom implements IAtom&lt;Space, Atom&gt; { } public void test() { ISpace&lt;?, ?&gt; spaceSupertype = new Space(); IAtom&lt;?, ?&gt; atomSupertype = new Atom(); Space space = (Space) spaceSupertype; // cast error Atom atom = (Atom) atomSupertype; // cast error } } </code></pre> <p><strong>Compiler error output:</strong></p> <pre><code>_SupertypeGenericTest.java:33: inconvertible types found : pinetag.data._SupertypeGenericTest.ISpace&lt;capture#341 of ?,capture#820 of ?&gt; required: pinetag.data._SupertypeGenericTest.Space Space space = (Space) spaceSupertype; ^ _SupertypeGenericTest.java:34: inconvertible types found : pinetag.data._SupertypeGenericTest.IAtom&lt;capture#94 of ?,capture#48 of ?&gt; required: pinetag.data._SupertypeGenericTest.Atom Atom atom = (Atom) atomSupertype; ^ 2 errors </code></pre> <p>Note: I'm using Netbeans latest trunk, bundled Ant, latest Java 6 release.<br> I tried using Ant from command line (Netbeans generates a build.xml file) but it results in same errors.</p> <p><strong>What is wrong?</strong><br> Is there an elegant way solve the problem?</p> <p>The strange thing is: Netbeans doesn't mark errors (not even warnings) in given code.</p> <p><strong>EDIT:</strong><br> No, now I understand <strong>nothing</strong>!<br> Eclipse 3.4.1 doesn't mark neither warnings nor errors, and compiles the code without trouble!!!<br> How can this be? I thought, using Ant from command line along with build.xml provided by Netbeans' would be neutral.<br> <strong>Am I missing something?</strong></p> <p><strong>EDIT 2:</strong><br> Using <strong>JDK7</strong> library and JDK7 code format, netbeans compiles without errors/warnings!<br> <strong>(I'm using 1.7.0-ea-b55)</strong></p> <p><strong>EDIT 3:</strong><br> Changed title to indicate that we're dealing with a javac bug.</p>
 

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