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POType-parameterized field of a generic class becomes invisible after upgrading to Java 7
 

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  1. POType-parameterized field of a generic class becomes invisible after upgrading to Java 7
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    <p>Now <a href="http://www.eclipse.org/downloads/packages/eclipse-ide-java-ee-developers/indigosr1">Eclipse Indigo SR1</a> with builtin <a href="http://www.oracle.com/technetwork/java/javase/downloads/java-se-jdk-7-download-432154.html">Java 7</a> support is finally out since a week or two, I'm migrating my playground projects from Helios SR2 + JDK 1.6_23 to Indigo SR1 + JDK 1.7.0. After a full rebuild of all projects, only one class has failed to compile. It's the following class which compiles and runs perfectly fine on Java 1.6 (and 1.5):</p> <pre class="lang-java prettyprint-override"><code>public abstract class Area&lt;A extends Area&lt;?&gt;&gt; implements Comparable&lt;Area&lt;?&gt;&gt; { private String name; private Area&lt;?&gt; parent; private Set&lt;A&gt; areas; protected Area(String name, A... areas) { this.name = name; this.areas = new TreeSet&lt;A&gt;(); for (A area : areas) { area.parent = this; this.areas.add(area); } } public Set&lt;A&gt; getAreas() { return areas; } // ... } </code></pre> <p>The line <code>area.parent = this;</code> fails with the following error on <code>parent</code>:</p> <blockquote> <p>The field Area&lt;capture#1-of ?>.parent is not visible </p> </blockquote> <p>After first suspecting the Eclipse compiler, I tried with plain <code>javac</code> from JDK 1.7.0, but it gives basically the same error whereas the <code>javac</code> from JDK 1.6.0_23 succeeds without errors.</p> <p>Changing the visibility to <code>protected</code> or default solves the problem. But the <strong>why</strong> is completely beyond me. I peeked around on <a href="http://bugs.sun.com">http://bugs.sun.com</a>, but I couldn't find any similar report. </p> <p>Another way to fix the compilation error is to replace all used <code>A</code> declarations inside the class by <code>Area&lt;?&gt;</code> (or to remove it altogether):</p> <pre class="lang-java prettyprint-override"><code>public abstract class Area&lt;A extends Area&lt;?&gt;&gt; implements Comparable&lt;Area&lt;?&gt;&gt; { private String name; private Area&lt;?&gt; parent; private Set&lt;Area&lt;?&gt;&gt; areas; protected Area(String name, Area&lt;?&gt;... areas) { this.name = name; this.areas = new TreeSet&lt;Area&lt;?&gt;&gt;(); for (Area&lt;?&gt; area : areas) { area.parent = this; this.areas.add(area); } } public Set&lt;Area&lt;?&gt;&gt; getAreas() { return areas; } // ... } </code></pre> <p>But this breaks the purpose of the getter. In case of for example the following class:</p> <pre><code>public class Country extends Area&lt;City&gt; { public Country(String name, City... cities) { super(name, cities); } } </code></pre> <p>I'd expect it to return <code>Set&lt;City&gt;</code>, not <code>Set&lt;Area&lt;?&gt;&gt;</code>.</p> <p>Which change in Java 7 has caused those type-parameterized fields to become invisible?</p>
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    1. USBalusC
    1. USBalusC
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    1. COIt *shouldn't*, but does changing the ctor from `protected` to `public` matter?
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      1. USDave Newton
    2. CO@DaveNewton: No, it doesn't matter.
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      1. USBalusC
 

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