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Java Forum / General / November 2007Howe to correctly parameterise a Class
Folks How do I correctly parameterise a Class? I have code like this: String classPath = "com.blah.bah.MyClass" Class clazz = Class.forName(classPath); Facade facade = (Facade) clazz.newInstance(); Facade is an interface and the class named by classPath will always implement this i/f. Do I simply do: Class<Facade> clazz = Class.forName(classPath); If not, what? TIA - Adam > String classPath = "com.blah.bah.MyClass" > Class clazz = Class.forName(classPath); [quoted text clipped - 4 lines] > > Do I simply do: Class<Facade> clazz = Class.forName(classPath); Not quite. Class.forName() is declared to return Class<?>, but you want Class<Facade>. > If not, what? You'll still need a cast: Class<Facade> clazz = (Class<Facade>) Class.forName(classPath); Facade facade = clazz.newInstance();  SignatureThomas [...] >> If not, what? > You'll still need a cast: > Class<Facade> clazz = (Class<Facade>) Class.forName(classPath); > Facade facade = clazz.newInstance(); I prefer to use a bit type-safer version of the above: Class<? extends Facade> clazz = Class.forName(classPath).asSubclass(Facade.class); Facade facade = clazz.newInstance(); piotr >> You'll still need a cast: >> Class<Facade> clazz = (Class<Facade>) Class.forName(classPath); [quoted text clipped - 5 lines] > = Class.forName(classPath).asSubclass(Facade.class); > Facade facade = clazz.newInstance(); Granted! I prefer yours, too. SignatureThomas Groovy! Many thanks.... Adam > [...] > [quoted text clipped - 10 lines] > > piotr Not to mention that this is more correct. The Class instance itself is the MyClass, not Facade, so Class<Facade> is just plain wrong, where as Class<? extends Facade> is accurate. SignatureDaniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/> Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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