Re: How to tell caller of an error if you cant change the signature of a method

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 14 Apr 2008 09:23:35 -0400

Message-ID:

<g-ednUUDmLhFx57VnZ2dnUVZ_uOmnZ2d@comcast.com>

Owen Jacobson wrote:

For completeness, here's an ExceptionHandler that knows about
IOExceptions:

public interface ExceptionHandler {
  public void handleException (Exception e);
}

public class IOExceptionHandler implements ExceptionHandler {
  public void handleException (Exception e) {
    try {
      throw e;

Or you could use 'if ( e instanceof IOException )', which preserves the stack
frame of the original exception and perhaps would be quicker, not that speed
matters to exception handling.

    } catch (IOException ioe) {
      System.err.println ("Handled an IOException: " + ioe);
    } catch (Exception e) {
      // Unexpected variety of failure here.
      throw new RuntimeException (e);
    }
  }
}

As illustrated, the design of ExceptionHandler as written demands that
implementations be prepared for *any* Exception, even if the caller
will only ever pass some specific type of Exception. The design could
be improved by providing specialized ExceptionHandler interfaces for
different implementations of IFoo, such that each handler only has to
deal with the exceptions that can actually be thrown.

Generics?

  public interface ExceptionHandler < E extends Exception >
  {
   public void handle( E e );
  }

  public class IOExceptionHandler implements ExceptionHandler <IOException>
  {
   public void handle( IOException e )
   {
     // implementation goes here
   }
  }

Pretty much any time I see run-time type checking built into the code, I
think, "This is a job for generics!"

Well, a job for polymorphism primarily, and generics frequently.

--
Lew