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copied!<p>You are running into <a href="http://docs.oracle.com/javase/tutorial/java/generics/erasure.html" rel="nofollow">type erasure</a>. You need to add another method to the <code>interface</code> that returns the <code>Class</code> instance that relates to the type parameter <code><T></code>, this will allow you to do runtime checks on that <code>Class</code>.</p> <p>I would accomplish this thus:</p> <pre><code>public interface MyInterface<T> { String run( T arg ); Class<T> type(); } </code></pre> <p>So the <code>interface</code> returns its type. N.B. all <code>interface</code> members are <code>public</code> by default - no need for the extra <code>public</code>.</p> <pre><code>public final class SomeImplementation1 implements MyInterface<String> { @Override public String run(final String arg) { return arg; } @Override public Class<String> type() { return String.class; } } @SuppressWarnings({"unchecked"}) public static <T> String run(final T arg) { for (final MyInterface<?> element : elements) { if (element.type().isAssignableFrom(arg.getClass())) { return ((MyInterface<T>) element).run(arg); } } throw new IllegalArgumentException("No element found."); } </code></pre> <p>The logic is that for each <code>MyInterface</code> you check whether the argument provided is safely castable to that <code>MyInterface</code>'s <code>type()</code>. If it is then you can cast the whole <code>MyInterface</code> to the <code>arg</code>'s type. This is unchecked as the compiler cannot verify this as compile time, but as you are manually doing a check this warning can be ignored.</p> <pre><code>public static void main(String[] args) throws Exception { elements = new LinkedList<>(); elements.add(new SomeImplementation1()); System.out.println(run("test")); System.out.println(run(1)); } </code></pre> <p>Output:</p> <pre><code>test Exception in thread "main" java.lang.IllegalArgumentException: No element found. at com.XXX.App.run(App.java:33) at com.XXX.App.main(App.java:55) </code></pre> <p>As expected.</p>

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