GCJ compiles fine, but I get cast exception

Hi all,

I try to run prefuse applying gcj.   There is a problem with the 
following cast :

    Graphics2D g2D = (Graphics2D)g;



gcj-info :
Using built-in specs.
Reading specs from /usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/libgcj.spec
rename spec lib to liborig
Target: x86_64-pc-linux-gnu
Configured with: 
/var/tmp/portage/sys-devel/gcc-4.1.2/work/gcc-4.1.2/configure 
--prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.1.2 
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/include 
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.1.2 
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.1.2/man 
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.1.2/info 
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.1.2/include/g++-v4 
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec 
--enable-nls --without-included-gettext --with-system-zlib 
--disable-checking --disable-werror --enable-secureplt --enable-multilib 
--enable-libmudflap --disable-libssp --enable-java-awt=gtk 
--enable-languages=c,c++,java,treelang,fortran --enable-shared 
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
Thread model: posix
gcc version 4.1.2 (Gentoo 4.1.2 p1.1)



Exception during event dispatch:
Exception in thread "prefuse_ActivityManager" 
java.lang.ClassCastException: gnu.java.awt.peer.gtk.GdkGraphics cannot 
be cast to java.awt.Graphics2D at 
prefuse.Display.paintComponent(Display.java:795)



Do you have an idea how to solve the Problem ?
Thank you

Ciamak