Re: Generics: instantiating an object from a class name in configuration

From:

usenet@chka.de (Christian Kaufhold)

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 13 Jul 2010 21:55:07 -0000

Message-ID:

<7faf.4c3ce0bb.a7d0@mokoscha.chka.de>

markspace <nospam@nowhere.com> wrote:

Lew wrote:

   try
   {
     // ClassCastException caught so this is safe
     @SuppressWarnings( "unchecked" )
     Class <Authenticator> clazz =
       (Class <Authenticator>) Class.forName( name );

     authenticator = clazz.newInstance();
   }

The following doesn't generate any warning messages and doesn't require
a @SuppressWarnings annotation. It's also a tad shorter. It will throw
ClassCastException if the type loaded isn't right, but that could be
caught too. I'm not sure it's better, but it is an alternative.

      try
      {
         Class<?> c = Class.forName( "test" );
         SomeType s = (SomeType) c.newInstance();

Do never use Class.newInstance(), it will pass through /any/ Throwable
that the actual code throws (it is actually one way to throw a checked exception
that is not declared). Instead use the explicit no-argument Constructor.

Strictly speaking, if a reflectively invoked method throws InterruptedException
(wrapped in the InvocationTargetException), one should also interrupt the current
Thread (or pass the InterruptedException on), as otherwise the interruption is
swallowed.