Blank constructor throwing NotImplementedException

[Lang Yang]

Hello guys,

I have seen some constructors throws a NotImplementedExpcetion when JDOC
says these constructors are supposed to just construct a blank class. I
thought for this case we just leave that constructor blank is good enough.
Is there any specific reason why we are throwing NotImplementedExceptions?

e.g.:
protected ImageInputStreamSpi() - Constructs a blank ImageInputStreamSpi. It
is up to the subclass to initialize instance variables and/or override
method implementations in order to provide working versions of all methods.
[0]

    protected ImageInputStreamSpi() throws NotImplementedException {
        // TODO: implement
        throw new NotImplementedException();
    }

Thanks,

Lang

[0] -
http://java.sun.com/j2se/1.4.2/docs/api/javax/imageio/spi/ImageInputStreamSpi.html#ImageInputStreamSpi()