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copied!<p>Due to <a href="http://docs.oracle.com/javase/tutorial/java/generics/erasure.html">type erasure</a>, you can't instantiate generic objects. Normally you could keep a reference to the <code>Class</code> object representing that type and use it to call <a href="http://download.oracle.com/javase/6/docs/api/java/lang/Class.html#newInstance%28%29"><code>newInstance()</code></a>. However, this only works for the default constructor. Since you want to use a constructor with parameters, you'll need to look up the <a href="http://docs.oracle.com/javase/6/docs/api/java/lang/reflect/Constructor.html"><code>Constructor</code></a> object and use it for the instantiation:</p> <pre><code>protected <T> T getProperty(String key, T fallback, Class<T> clazz) { String value = properties.getProperty(key); if (value == null) { return fallback; } else { //try getting Constructor Constructor<T> constructor; try { constructor = clazz.getConstructor(new Class<?>[] { String.class }); } catch (NoSuchMethodException nsme) { //handle constructor not being found } //try instantiating and returning try { return constructor.newInstance(value); } catch (InstantiationException ie) { //handle InstantiationException } catch (IllegalAccessException iae) { //handle IllegalAccessException } catch (InvocationTargetException ite) { //handle InvocationTargetException } } } </code></pre> <p>However, seeing how much trouble it is to achieve this, including the performance cost of using reflection, it's worth looking into other approaches first. </p> <p>If you absolutely need to take this route, and if <code>T</code> is limited to a distinct set of types known at compile time, a compromise would be to keep a static <code>Map</code> of <code>Constructor</code>s, which is loaded at startup - that way you don't have to dynamically look them up at every call to this method. For example a <code>Map<String, Constructor<?>></code> or <code>Map<Class<?>, Constructor<?>></code>, which is populated using a <a href="http://download.oracle.com/javase/tutorial/java/javaOO/initial.html">static block</a>.</p>

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