Re: Visitor pattern vs if-ladder

From:
Mark Space <markspace@sbc.global.net>
Newsgroups:
comp.lang.java.programmer
Date:
Thu, 23 Apr 2009 09:50:43 -0700
Message-ID:
<O%0Il.15090$hc1.6774@flpi150.ffdc.sbc.com>
I found a way to get rid of the try-catch. So no the method won't throw
exceptions as part of its normal operation if it has more than one
interface to parse through.

This should remove the biggest potential performance issue.

The trick is to use "isAssignableFrom()" before actually using
"asSubclass()".

     public static <T> Class<? extends T> asSubclassOf( Class<T> type,
             Object o )
     {
         if( !type.isInstance( o ) ) {
             return null; // or throw exception
         }
         Class<?> classX = o.getClass();
         do {
             Class<?>[] interfaces = classX.getInterfaces();
             for( Class<?> c : interfaces ) {
                 Class<? extends T> subType = null;
                 if( type.isAssignableFrom( c ) ) {
                     return c.asSubclass( type );
                 }
             }
             classX = classX.getSuperclass();
         } while( classX != null );
         return null; // should never reach here
     }

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