Request for non-throwing cast!

Question

Hi there,
here's something that I'd love to see in Java 1.5:
A non-throwing cast operator that returns null if the operand is either null or is not of the requested type.
(For C++ afficionados: Like "dynamic_cast" applied to pointers.
For C# followers: Like operator "as").
Since adding a new operator to Java is vastly unrealistic, what about adding a member function
to java.lang.Class?
I'm proposing the addition of the following member function to java.lang.Class<T>:
public T as(Object source)
return this.isInstance(source) ? (T)source : null;

Answer 1

How about this, anyway ?
package com.paperstack.generics;
* Static methods for use with generics in casting
* @author Dave Minter
public class Casts {
   * Generic safe cast
   * @param c The class type to which o should be cast, represented as a Class object
   * @param o The object to be cast
   * @return The object cast to the appropriate type, or null if this would otherwise produce a ClassCastException
  public static <C> C as(Class<C> c,Object o) {
     if( c.isInstance(o) ) return (C)o;
     return null;
}Invoked thus:
import static com.paperstack.generics.Casts.*;
import static java.lang.System.*;
public class Boom {
  public static void main(String... argv) {
     out.println(as(Integer.class,"Hello"));
     out.println(as(Integer.class,"42"));
     out.println(as(Integer.class,new Integer(43)));
     out.println(as(Integer.class,44));
     out.println(as(Integer.class,null));
}It's not quite as elegant as yours, but with the static import it's fairly tidy.
Incidentally, should one be able to do a static import of a class in the default package ? The only reason the above is in a proper package is that I tried creating my illustration in the default package, but the Boom class choked when I tried to do "static import Casts.*". Or is that a bug ?
D.