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    <p>It is true that generics aren't generally known at runtime in Java, because they are implemented with Type Erasure.</p> <h2>Reflecting Generics?</h2> <p>However, you can stil extract some valuable information about the <strong>declared types</strong> (NOT the runtime objects' types), as presented in Ian Roberston's article <em><a href="http://www.artima.com/weblogs/viewpost.jsp?thread=208860" rel="nofollow noreferrer">Reflecting Generics</a></em> and Prenkov's article <em><a href="http://tutorials.jenkov.com/java-reflection/generics.html" rel="nofollow noreferrer">Java Reflection: Generics</a></em>.</p> <h2>Background on Generics and Type Erasure</h2> <p>Generics where introduced while conserving backwards compatibility at the source qnd binary level, hence some of their limitation, like:</p> <ul> <li>the impossibility to have a short-hand form without at least some indicator for generics support (here, the so-called <strong>diamond operator</strong> <code>&lt;&gt;</code>),</li> <li>the impossibility to inspect generic-types at runtime, because they had to be implemented with <strong><a href="http://docs.oracle.com/javase/tutorial/java/generics/erasure.html" rel="nofollow noreferrer">Type Erasure</a></strong>.</li> </ul> <h3>Further Reading</h3> <ul> <li>From <a href="http://docs.oracle.com/javase/tutorial/" rel="nofollow noreferrer">The Java Tutorial</a>: <ul> <li>section on <a href="http://docs.oracle.com/javase/tutorial/java/generics/gentypes.html" rel="nofollow noreferrer">Generic Types</a></li> <li>section on <a href="http://docs.oracle.com/javase/tutorial/java/generics/gentypeinference.html#type-inference-instantiation" rel="nofollow noreferrer">Type Inference and Instantiation of Generic Classes</a></li> </ul></li> <li>From the Java <a href="http://docs.oracle.com/javase/specs/" rel="nofollow noreferrer">Language Specifications</a> (JLS): <ul> <li><a href="http://docs.oracle.com/javase/specs/jls/se5.0/html/j3TOC.html" rel="nofollow noreferrer">Java SE 5's JLS</a> section on <a href="http://docs.oracle.com/javase/specs/jls/se5.0/html/typesValues.html" rel="nofollow noreferrer">Types, Values and Variables</a></li> <li><a href="http://docs.oracle.com/javase/specs/jls/se7/html/index.html" rel="nofollow noreferrer">Java SE 7's JLS</a> section on <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html" rel="nofollow noreferrer">Types, Values and Variables</a></li> </ul></li> <li>From good StackOverflow questions: <ul> <li><a href="https://stackoverflow.com/questions/1206028/java-raw-type-and-generics-interaction">Java Raw Type and generics interaction</a></li> </ul></li> <li>Others: <ul> <li>IBM Developer Series: <a href="http://www.ibm.com/developerworks/java/library/j-jtp01255/index.html" rel="nofollow noreferrer">Java Theory and Practice: Generics Gotchas</a> (especially the sections <strong>The Road Not Taken</strong>, <strong>Generifying Existing Classes</strong> and <strong>Implications of Erasure</strong>).</li> </ul></li> </ul>
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    1. COOk, then how does Guice figure out what Provider is appropriate, as in the example I gave?
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      1. USJohn Ericksen
    2. COBasically, if you specified a concrete type parameter in the code, then Guice can see the parameter that method was *declared* with via reflection.
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      1. USLouis Wasserman
    3. CO@Anony-Mousse: Sorry, I was still typing this while you were adding your comment. I point to Robertson's article using these, indeed. (I usually write answers in small bursts to prevent typing for nothing in questions get closed, or I accidentally close a Window, and because I think it can avoid multiple people typing in very similar answers if they see that one is already on the way). Thanks for pointing it out though.
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