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POCompiler warning when casting to generic method type variable in Java
 

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    <p><strong>Edit:</strong> I initially accepted thejh's answer, but I wasn't really satisfied with it since I wanted to make proper use of generics. So, I kept doing research and found a solution. Read about it in <a href="https://stackoverflow.com/questions/4117500/compiler-warning-when-casting-to-generic-method-type-variable-in-java/4153524#4153524">my answer</a> below.</p> <hr> <p>Here's a little self-contained piece of Java code which shows what I'm trying to do. It compiles, runs, and behaves correctly.</p> <pre><code> 1 import java.lang.reflect.Method; 2 import java.lang.reflect.InvocationTargetException; 3 4 public class Example 5 { 6 public static &lt;T&gt; void foo(Method method, String target, Object argument, T expectedReturn) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException 7 { 8 T actualReturn = (T) method.invoke(target, argument); 9 System.out.print(actualReturn.equals(expectedReturn)); 10 } 11 12 public static void main(String[ ] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException 13 { 14 foo(String.class.getMethod("charAt", int.class), "test", 1, 'e'); 15 } 16 } </code></pre> <p>Running this prints <code>true</code> to the console, which is what I expected. What's bothering me is that, due to the cast on line 8, I'm getting a warning when I compile it, as follows (jGRASP is my IDE, by the way).</p> <blockquote> <p>----jGRASP exec: javac -g -Xlint:unchecked Sandbox.java<br> Sandbox.java:8: warning: [unchecked] unchecked cast<br> found : java.lang.Object<br> required: T<br> 1 warning </p> <p>----jGRASP: operation complete.</p> </blockquote> <p>Originally, I tried line 8 without the cast, but that failed to compile with an error complaining about finding an <code>Object</code> when it required <code>T</code> (<code>invoke</code> returns an <code>Object</code>). Later on, I rewrote it like this, blindly hoping to get rid of the warning.</p> <pre><code>T actualReturn = method.getReturnType( ).cast(method.invoke(target, argument)); </code></pre> <p>But that gives a compile error that I can't make head nor tail of.</p> <blockquote> <p>----jGRASP exec: javac -g -Xlint:unchecked Sandbox.java<br> Sandbox.java:8: incompatible types<br> found : capture#898 of ?<br> required: T<br> 1 error </p> <p>----jGRASP wedge: exit code for process is 1.<br> ----jGRASP: operation complete.</p> </blockquote> <p>And that number next to <code>capture#</code> is different each time I try to compile with that same line of code.</p> <p>So, what exactly is the problem? Why am I getting the warning when I cast the object returned by invoke to the type variable? Does that indicate that I'm doing something wrong? How can I write this so that the warning goes away? And I'd prefer not to suppress it with an annotation, as that doesn't seem like much of a solution to me.</p>
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