Re: Java/OOP Question/Problem

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 09 Feb 2008 17:39:51 -0500

Message-ID:

<z6OdnRBeRu0ltjPanZ2dnUVZ_rignZ2d@comcast.com>

DBloke wrote:

I am getting the class cast exception because I am trying to trick the
JVM into believing my ImageWindow is actually an ImageFrame by casting
myImageFrame to a JFrame and then a Frame and passing it to the method
expecting an ImageFrame.

I understand why this can be dangerous, but the only method I wanted to
call on the Frame, JFrame or ImageFrame was to resize it.

I really just want to be able to zoom in and out of an image whilst
maintaining a good representation of the original image, I also want to
be able to zoom in to an area of a large image so that the area I am
zooming in to is clear and not too pixelated or blurred, I may also need
to copy and paste the zoomed in to area.

I know Java provides a scale image method but the image becomes too
pixelated after x32 on a 12 mega-pixel image.

AffineTransform and related classes are a way to resize images, and they have
options for different dithering IIRC.

You cannot get away with casting something to something that it isn't. You
still haven't shown us the relevant code, so there's no way to be specific,
but unless there's an actual inheritance relationship between 'ImageWindow'
and 'ImageFrame' casting between them will never work.

Remember that widening conversions ("upcasts") do not require an explicit cast
operator, narrowing conversions ("downcasts") do.

The way to mitigate danger in legitimate casts is to catch the
ClassCastException and handle it. You will always get that exception if
you're trying to cast to something the object can never be.

--
Lew